• Advertisement
Sign in to follow this  

OpenGL OpenGL to DirectX

This topic is 1080 days old which is more than the 365 day threshold we allow for new replies. Please post a new topic.

If you intended to correct an error in the post then please contact us.

Recommended Posts

Hi, I'm new to game programming and I want to move to 3d game development, I have this problem choosing whether I choose OpenGL first then learn DirectX or learn DirectX then OpenGL, Almost all the tutorial I found in DirectX only show how to make this triangle. I really want to learn DirectX first but I cant find any good tutorial that actually make a simple 3d game, like loading .fbx file, controlling character with animation and collision detection. So I think that if I learned OpenGL it will be easy to learn DirectX. Or should I go learn DirectX straight? if yes, is there a good tutorial that will make a simple 3d game for directx? i look for Introduction to 3D Game Programming with Direct3D 11.0 by frank de luna, but it's all about rendering.

Share this post


Link to post
Share on other sites
Advertisement

Welcome to gamedev, avahdon.

 

First step: read the Beginner's FAQ. In particular, note the suggestion "Browse and search before you ask, to see if your question has already been asked and answered." There's a search box in the upper right-hand corner of every forum screen. You'll find that your questions have been asked hundreds of times, and you'll gain a lot of info by reading the responses to those questions.

 

Second: In that FAQ, also note the admonition: "This" versus "that" threads are considered flame bait and will usually be closed on sight. Such questions have usually been asked before, several times, so there should be no need to ask them again.

 

Asking questions like "DirectX or OpenGL?" will result in a variety of responses that will not likely help you much at all. I.e., responses will likely be:

 

1. Always start with DirectX.

2. No! Always start with OpenGL.

3. Either one. Just choose and start in learning.

4. No! Don't start with either one - start with [ fill in a dozen suggestions ]

etc.

etc.

happy.png

Share this post


Link to post
Share on other sites

Try both API's for a while and decide yourself what is best, as they both perform generally the same job in the end of displaying graphics, and holy wars aside it's all just personal preference. 

 

In the end what matters is writing the solution with the right tool for the job.

 

Good luck and have fun!

Share this post


Link to post
Share on other sites

Hi avadhon!

 

No, you won't find a simple tutorial for what you are seeking: something that does not render a triangle or a cube and resembles a simple game. Those are long a extremely complicated. I am a bit in the same shoes as you: I am experiencing DirectX 11 for the first time. Now granted, I am a self assessed DirectX 9 expert, but DirectX 11 is completely new for me and I am writing a full engine (actually more like and incremental port) from scratch, minus physics. And I can tell you that this engine will be around 500 KiB of code at minimum. Probably 700 KiB. Add to that an external physics engine. There is no way for a tutorial to even cover 100 KiB of code in an easy manner.

 

But don't let this discourage you! There is a reason most tutorials only show a triangle. That is the base of what you need. You need to learn once the basics of window and device creation. This can be done in DirectX or OpenGl. Not important at all. But once you have this done, I would recommend to abstract away and ignore all this setup and busy work and focus on that triangle. The ideal 3D program that displays a triangle should have one line of code that creates the triangle buffer, one line of code for each vertex in the triangle and one line of code to render it using a camera.

 

Once you are very comfortable with creating a triangle from scratch, you can do basically anything. Learning to create meshes and what can be done with it is far more important that how to set up a 3D device.

 

As for OpenGL or DirectX, if you are a beginner and only want to do simple to medium stuff, the choice is irrelevant. Don't let fan boys sway you one way or the other. They are both good in their own way. And if you go with a right handed coordinate system, the same camera and mesh code can run on both.

 

But if you want the highest of the high level of graphics, super AAA quality rendering, then OpenGl is inferior. Maybe the latest version is great, but the ones I tried were a lot behind. For starters, a big chunk of OpenGL is implemented in the GPU driver. There is a huge quality gap between supper cheap GPUs never meant to do real rendering work and high quality stuff. DirectX if capable of rendering what you wish will have a pretty consistent quality, but of course the low end GPU will run like shit. You will have a beautiful picture that runs a 2 FPS. OpenGL is really not universally capable of of pixel prefect rendering, but does scale OK.

 

Second, OpenGL does not generally allow you to load precompiled shaders. You need to compile them at runtime. This is a huge disadvantage since modern heavy weight engines use hundreds of KiB of shader code. One of my DirectX 9 projects can spend literally 5 minutes just compiling shaders, but is able to load those precompiled shaders in seconds from a binary blog.

 

The real question is what you want to do. Do you want to learn the core of 3D rendering? That is procedural meshes and shaders. Do you want to learn rendering in general? Choose one: DirectX or OpenGL. Do you want to write a real game? Don't use either. Start with something like Unity.

Share this post


Link to post
Share on other sites

The real question is what you want to do. Do you want to learn the core of 3D rendering? That is procedural meshes and shaders. Do you want to learn rendering in general? Choose one: DirectX or OpenGL. Do you want to write a real game? Don't use either. Start with [a game engine like Unity, or at least an existing OpenGL/DirectX wrapper like Ogre/Horde3D/etc].

^^ this (slightly edited for my opinion).

Share this post


Link to post
Share on other sites

It is possible to write a real game in raw DirectX or opengl. So long as your goals aren't huge, and your idea simple enough it is manageable and achievable. 

 

I am currently writing a game in raw DirectX 11 after using xna for a while, and despite the fact I have very little free time I am making good progress despite not having touched DirectX since dabbling with directdraw 6 in 1999.

 

I accept though that my game might be prettier and faster to produce if I'd just picked up unity and ported my c# code, but I'd never have learned so much so fast, so it's "horses for courses" as they say...

Share this post


Link to post
Share on other sites

thanks all for the answer, i try unity and i find it very easy, you can make games from copy pasting, but i want to know how to create my own game from scratch, i have lots of free time right now so i want to learn the core of game dev, one more question, if i choose to start in directx, will it be easy to switch to opengl?  or vise versa? like what happen to me when i learn c#, i know c++ so it become smooth learning. then learning php is much more easier. will it be the same learning when i learn one api, it will be easy to learn the other api? and should i start with dx9 or jump to dx11? i already done 2d with sdl, i made ping pong and some mario like games. 

Share this post


Link to post
Share on other sites

if i choose to start in directx, will it be easy to switch to opengl?

Why do you need to learn both anyway?
Why don’t you just learn the one that is most practical and useful?
 
And later in life, on a rainy day, if you are really bored and curious, then you can decide if you want to bother learning the other.

I don’t understand why you’ve decided straight out-of-the-gate that you simply must learn both—for no practical reason apparently—and you are so hung up on this strange decision of yours that it has become the stumbling block in your moving forward.

 

When I was deciding which to learn first, I didn’t ask, “Which makes the other easier to learn oh noes!”, I asked, “Which one do I need for what I want to do right now?”.

Direct3D 9 was the obvious choice for me because I wanted to make games on PC, and then years later iOS devices appeared and then I decided to learn OpenGL.
 
 

and should i start with dx9 or jump to dx11?

Direct3D 11.
All API’s representing the current and next generation in graphics are based off Direct3D 11 or Direct3D 12 (that is actually backwards—Direct3D 12 is based off Mantle, but it doesn’t matter which came first).


L. Spiro

Share this post


Link to post
Share on other sites

 

When I was deciding which to learn first, I didn’t ask, “Which makes the other easier to learn oh noes!”, I asked, “Which one do I need for what I want to do right now?”.

Direct3D 9 was the obvious choice for me because I wanted to make games on PC, and then years later iOS devices appeared and then I decided to learn OpenGL.
 

 

is it easy to transfer from direct3d9 to opengGL? same reason i want to learn both. and im not saying im going to learn both, i just want to know if it is easy to jump to another api.

Share this post


Link to post
Share on other sites

thanks all for the answer, i try unity and i find it very easy, you can make games from copy pasting

You can make a game with D3D by copy pasting too, but you won't learn much that way...
You didn't answer if you want to learn how to program a GPU (what GL/D3D are for) or just want to make a game.
Why not make a game from scratch (no copy and pasting) on a real game engine first?
If you don't want to use an existing engine (for whatever reason), you can still use an existing graphics library, which is just a wrapper around GL/etc.
E.g. Look at Horde3D - you still have to write all your own C++ code, but they've abstracted GL from an unwieldy GPU-API into an understandable API designed for people who are making their own game engines.

i want to learn the core of game dev

On a professional game programming team of 20 staff, only one of them will write D3D/GL code - it's a specialist engine development skill, not a core game development skill.

if i choose to start in directx, will it be easy to switch to opengl? or vise versa?

Yes. They're both just APIs for sending commands to the GPU. Once you understand how GPU's work, then learning a 2nd/3rd/4th API is much easier.

Share this post


Link to post
Share on other sites

 

 

When I was deciding which to learn first, I didn’t ask, “Which makes the other easier to learn oh noes!”, I asked, “Which one do I need for what I want to do right now?”.

Direct3D 9 was the obvious choice for me because I wanted to make games on PC, and then years later iOS devices appeared and then I decided to learn OpenGL.
 

 

is it easy to transfer from direct3d9 to opengGL? same reason i want to learn both. and im not saying im going to learn both, i just want to know if it is easy to jump to another api.

 

 

Do not waste time with Direct3D 9. Direct3D 11 is a better structured API, easier to learn, more powerful and it support down-level hardware trough feature levels (down to SM 2.0x GPUs).

Yes, you cannot target Windows XP with Direct3D 11, but who cares? When you will be able to release something to the public, Windows XP will be like <1% or less of gaming PCs (actually Steam says it's around 4%).

Edited by Alessio1989

Share this post


Link to post
Share on other sites

I would start with OpenGL 3.x/4.x and then go to DX11 once you grasped the initial concepts.

 

The reason is there are no good in-depth DX11 tutorials the likes of which http://www.arcsynthesis.org/gltut/ but once you know the basics of graphics programming DX11 is more straightforward and atleast I had issues finding debugging tools that worked for OpenGL, while you can use RenderDoc or VisualStudio for DX11, which makes development soooo much easier.

Share this post


Link to post
Share on other sites

 

The real question is what you want to do. Do you want to learn the core of 3D rendering? That is procedural meshes and shaders. Do you want to learn rendering in general? Choose one: DirectX or OpenGL. Do you want to write a real game? Don't use either. Start with [a game engine like Unity, or at least an existing OpenGL/DirectX wrapper like Ogre/Horde3D/etc].

^^ this (slightly edited for my opinion).

 

 

Well, I did suggest Unity because it is a "big boy" engine that does everything and is very well documented and supported. If he want to create a game, a full featured engine is best, but not necessarily Unity. But Unity also seems a bit more easy to get you hands on and grasp than the CryEngine or Unreal. There are also a ton of engines available, but quite a few have to problem of allowing for graphics that are at most from 2006.

 

But if the goal is not to write a real game, indeed I would recommend a wrapper. Can be something simple as DirectX TK. Or one of the mini-frameworks from a few popular bloggers. I would not recommend DXUT. And Ogre without precompiled headers takes so long to compile that you can have a meal each time.

Share this post


Link to post
Share on other sites

 


But if you want the highest of the high level of graphics, super AAA quality rendering, then OpenGl is inferior. Maybe the latest version is great, but the ones I tried were a lot behind. For starters, a big chunk of OpenGL is implemented in the GPU driver. There is a huge quality gap between supper cheap GPUs never meant to do real rendering work and high quality stuff.
[citation needed]

 

 

I can't offer you a citation, only anecdotal evidence.

 

In historic order:

1. Linux. This is probably the problem of early Linux drivers and not a real problem with OpenGL, but OpenGL reliability on Linux was very bad. Sure, if you ran glgears there were no problems. But if you tried to do more complicated stuff, some things would not render exactly as expected with no way to fix it except to either try to change X setting and mess around with the driver or move to another PC. There were small bugs that effected only parts of it, allowing you to render the scene but some effects would not show up.

2. Windows Vista + some ATI cards. When Vista came out, some ATI cards had broken OpenGL drivers and it took so many months for them to fix it that I gave up on Vista. The performance was very bad.

3. Even today, there can be subtle differences. Things like Toksvig specular AA are highly dependent on the exact behavior of the GPU filtering system. Even right now if I tried, I can get at least 3 different results on 3 different PCs. Same code, same resolution, different GPUs. The probability of getting it pixel perfect is less than in DirectX and OpenGL has no mechanic to report to you that it is doing stuff differently than you would expect. It says: OK, rendered corectly! And indeed there is output on the screen. And if you examine it superficially it looks OK. Maybe just by a little and I had bad luck. But I'm pretty sure it is not higher.

 

What I got out of all these experiences is a common theme of slightly less reliability. This is of course an issue only on the PC. If you target some hardware that only has OpenGL and historically has only had OpenGL and everybody is using OpenGL do do 100% of the graphics stuff, there will be probably no such issues.

Share this post


Link to post
Share on other sites

Your API decision should be in the back of your mind for now. The bigger questions to ask if you are going to go the API route are :

Do I have the basic knowledge about 3D rendering, lighting , transform , shaders, the graphics pipeline....Without the fundamentals you are going to be stuck in an endless loop of cut-paste-I don't understand this code-post question of a forum for an answer...repeat....

Do you have an background in basic linear algebra ?

Do you have an understanding of the fundamentals of computer graphics.

These should be more important to you than what API to use..because in the end it comes down to syntax...they both do the same thing.

Share this post


Link to post
Share on other sites

I personally use OpenGL because is clossplatform and the differences of performance with Direct3D are gone. I think also Direct3D has a conflict, is not vendor-neutral standard.

 

Check this nvidia blog:

 

http://blogs.nvidia.com/blog/2014/03/20/opengl-gdc2014/

 

AZDO is effectively dead.

 

With Vulkan and D3D12 on the way, nobody (outside of tech-demos) is going to primarily write code in the AZDO style because it's essentially unportable to other APIs: no other API works that way, and porting will be non-trivial; it's a complete re-architecting.

 

To be brutally honest, whether or not an API is cross-platform should be the least concern of anybody starting out.  They've enough to learn on one platform; learning on two (or more) is just not being helpful.  Better to focus on tools, support, documentation, resources and driver quality.  I want to highlight the latter because it's vital for a beginner to be able to tell the difference between "did I screw up?" and "have I got a weird driver bug?"  Good driver quality gives them the ability to tell that difference with more confidence.  Having to continually fight the drivers ... doesn't.

Share this post


Link to post
Share on other sites
Sign in to follow this  

  • Advertisement
  • Advertisement
  • Popular Tags

  • Advertisement
  • Popular Now

  • Similar Content

    • By getoutofmycar
      I'm having some difficulty understanding how data would flow or get inserted into a multi-threaded opengl renderer where there is a thread pool and a render thread and an update thread (possibly main). My understanding is that the threadpool will continually execute jobs, assemble these and when done send them off to be rendered where I can further sort these and achieve some cheap form of statelessness. I don't want anything overly complicated or too fine grained,  fibers,  job stealing etc. My end goal is to simply have my renderer isolated in its own thread and only concerned with drawing and swapping buffers. 
      My questions are:
      1. At what point in this pipeline are resources created?
      Say I have a
      class CCommandList { void SetVertexBuffer(...); void SetIndexBuffer(...); void SetVertexShader(...); void SetPixelShader(...); } borrowed from an existing post here. I would need to generate a VAO at some point and call glGenBuffers etc especially if I start with an empty scene. If my context lives on another thread, how do I call these commands if the command list is only supposed to be a collection of state and what command to use. I don't think that the render thread should do this and somehow add a task to the queue or am I wrong?
      Or could I do some variation where I do the loading in a thread with shared context and from there generate a command that has the handle to the resources needed.
       
      2. How do I know all my jobs are done.
      I'm working with C++, is this as simple as knowing how many objects there are in the scene, for every task that gets added increment a counter and when it matches aforementioned count I signal the renderer that the command list is ready? I was thinking a condition_variable or something would suffice to alert the renderthread that work is ready.
       
      3. Does all work come from a singular queue that the thread pool constantly cycles over?
      With the notion of jobs, we are basically sending the same work repeatedly right? Do all jobs need to be added to a single persistent queue to be submitted over and over again?
       
      4. Are resources destroyed with commands?
      Likewise with initializing and assuming #3 is correct, removing an item from the scene would mean removing it from the job queue, no? Would I need to send a onetime command to the renderer to cleanup?
    • By Finalspace
      I am starting to get into linux X11/GLX programming, but from every C example i found - there is this XVisualInfo thing parameter passed to XCreateWindow always.
      Can i control this parameter later on - when the window is already created? What i want it to change my own non GLX window to be a GLX window - without recreating. Is that possible?
       
      On win32 this works just fine to create a rendering context later on, i simply find and setup the pixel format from a pixel format descriptor and create the context and are ready to go.
       
      I am asking, because if that doesent work - i need to change a few things to support both worlds (Create a context from a existing window, create a context for a new window).
    • By DiligentDev
      This article uses material originally posted on Diligent Graphics web site.
      Introduction
      Graphics APIs have come a long way from small set of basic commands allowing limited control of configurable stages of early 3D accelerators to very low-level programming interfaces exposing almost every aspect of the underlying graphics hardware. Next-generation APIs, Direct3D12 by Microsoft and Vulkan by Khronos are relatively new and have only started getting widespread adoption and support from hardware vendors, while Direct3D11 and OpenGL are still considered industry standard. New APIs can provide substantial performance and functional improvements, but may not be supported by older hardware. An application targeting wide range of platforms needs to support Direct3D11 and OpenGL. New APIs will not give any advantage when used with old paradigms. It is totally possible to add Direct3D12 support to an existing renderer by implementing Direct3D11 interface through Direct3D12, but this will give zero benefits. Instead, new approaches and rendering architectures that leverage flexibility provided by the next-generation APIs are expected to be developed.
      There are at least four APIs (Direct3D11, Direct3D12, OpenGL/GLES, Vulkan, plus Apple's Metal for iOS and osX platforms) that a cross-platform 3D application may need to support. Writing separate code paths for all APIs is clearly not an option for any real-world application and the need for a cross-platform graphics abstraction layer is evident. The following is the list of requirements that I believe such layer needs to satisfy:
      Lightweight abstractions: the API should be as close to the underlying native APIs as possible to allow an application leverage all available low-level functionality. In many cases this requirement is difficult to achieve because specific features exposed by different APIs may vary considerably. Low performance overhead: the abstraction layer needs to be efficient from performance point of view. If it introduces considerable amount of overhead, there is no point in using it. Convenience: the API needs to be convenient to use. It needs to assist developers in achieving their goals not limiting their control of the graphics hardware. Multithreading: ability to efficiently parallelize work is in the core of Direct3D12 and Vulkan and one of the main selling points of the new APIs. Support for multithreading in a cross-platform layer is a must. Extensibility: no matter how well the API is designed, it still introduces some level of abstraction. In some cases the most efficient way to implement certain functionality is to directly use native API. The abstraction layer needs to provide seamless interoperability with the underlying native APIs to provide a way for the app to add features that may be missing. Diligent Engine is designed to solve these problems. Its main goal is to take advantages of the next-generation APIs such as Direct3D12 and Vulkan, but at the same time provide support for older platforms via Direct3D11, OpenGL and OpenGLES. Diligent Engine exposes common C++ front-end for all supported platforms and provides interoperability with underlying native APIs. It also supports integration with Unity and is designed to be used as graphics subsystem in a standalone game engine, Unity native plugin or any other 3D application. Full source code is available for download at GitHub and is free to use.
      Overview
      Diligent Engine API takes some features from Direct3D11 and Direct3D12 as well as introduces new concepts to hide certain platform-specific details and make the system easy to use. It contains the following main components:
      Render device (IRenderDevice  interface) is responsible for creating all other objects (textures, buffers, shaders, pipeline states, etc.).
      Device context (IDeviceContext interface) is the main interface for recording rendering commands. Similar to Direct3D11, there are immediate context and deferred contexts (which in Direct3D11 implementation map directly to the corresponding context types). Immediate context combines command queue and command list recording functionality. It records commands and submits the command list for execution when it contains sufficient number of commands. Deferred contexts are designed to only record command lists that can be submitted for execution through the immediate context.
      An alternative way to design the API would be to expose command queue and command lists directly. This approach however does not map well to Direct3D11 and OpenGL. Besides, some functionality (such as dynamic descriptor allocation) can be much more efficiently implemented when it is known that a command list is recorded by a certain deferred context from some thread.
      The approach taken in the engine does not limit scalability as the application is expected to create one deferred context per thread, and internally every deferred context records a command list in lock-free fashion. At the same time this approach maps well to older APIs.
      In current implementation, only one immediate context that uses default graphics command queue is created. To support multiple GPUs or multiple command queue types (compute, copy, etc.), it is natural to have one immediate contexts per queue. Cross-context synchronization utilities will be necessary.
      Swap Chain (ISwapChain interface). Swap chain interface represents a chain of back buffers and is responsible for showing the final rendered image on the screen.
      Render device, device contexts and swap chain are created during the engine initialization.
      Resources (ITexture and IBuffer interfaces). There are two types of resources - textures and buffers. There are many different texture types (2D textures, 3D textures, texture array, cubmepas, etc.) that can all be represented by ITexture interface.
      Resources Views (ITextureView and IBufferView interfaces). While textures and buffers are mere data containers, texture views and buffer views describe how the data should be interpreted. For instance, a 2D texture can be used as a render target for rendering commands or as a shader resource.
      Pipeline State (IPipelineState interface). GPU pipeline contains many configurable stages (depth-stencil, rasterizer and blend states, different shader stage, etc.). Direct3D11 uses coarse-grain objects to set all stage parameters at once (for instance, a rasterizer object encompasses all rasterizer attributes), while OpenGL contains myriad functions to fine-grain control every individual attribute of every stage. Both methods do not map very well to modern graphics hardware that combines all states into one monolithic state under the hood. Direct3D12 directly exposes pipeline state object in the API, and Diligent Engine uses the same approach.
      Shader Resource Binding (IShaderResourceBinding interface). Shaders are programs that run on the GPU. Shaders may access various resources (textures and buffers), and setting correspondence between shader variables and actual resources is called resource binding. Resource binding implementation varies considerably between different API. Diligent Engine introduces a new object called shader resource binding that encompasses all resources needed by all shaders in a certain pipeline state.
      API Basics
      Creating Resources
      Device resources are created by the render device. The two main resource types are buffers, which represent linear memory, and textures, which use memory layouts optimized for fast filtering. Graphics APIs usually have a native object that represents linear buffer. Diligent Engine uses IBuffer interface as an abstraction for a native buffer. To create a buffer, one needs to populate BufferDesc structure and call IRenderDevice::CreateBuffer() method as in the following example:
      BufferDesc BuffDesc; BufferDesc.Name = "Uniform buffer"; BuffDesc.BindFlags = BIND_UNIFORM_BUFFER; BuffDesc.Usage = USAGE_DYNAMIC; BuffDesc.uiSizeInBytes = sizeof(ShaderConstants); BuffDesc.CPUAccessFlags = CPU_ACCESS_WRITE; m_pDevice->CreateBuffer( BuffDesc, BufferData(), &m_pConstantBuffer ); While there is usually just one buffer object, different APIs use very different approaches to represent textures. For instance, in Direct3D11, there are ID3D11Texture1D, ID3D11Texture2D, and ID3D11Texture3D objects. In OpenGL, there is individual object for every texture dimension (1D, 2D, 3D, Cube), which may be a texture array, which may also be multisampled (i.e. GL_TEXTURE_2D_MULTISAMPLE_ARRAY). As a result there are nine different GL texture types that Diligent Engine may create under the hood. In Direct3D12, there is only one resource interface. Diligent Engine hides all these details in ITexture interface. There is only one  IRenderDevice::CreateTexture() method that is capable of creating all texture types. Dimension, format, array size and all other parameters are specified by the members of the TextureDesc structure:
      TextureDesc TexDesc; TexDesc.Name = "My texture 2D"; TexDesc.Type = TEXTURE_TYPE_2D; TexDesc.Width = 1024; TexDesc.Height = 1024; TexDesc.Format = TEX_FORMAT_RGBA8_UNORM; TexDesc.Usage = USAGE_DEFAULT; TexDesc.BindFlags = BIND_SHADER_RESOURCE | BIND_RENDER_TARGET | BIND_UNORDERED_ACCESS; TexDesc.Name = "Sample 2D Texture"; m_pRenderDevice->CreateTexture( TexDesc, TextureData(), &m_pTestTex ); If native API supports multithreaded resource creation, textures and buffers can be created by multiple threads simultaneously.
      Interoperability with native API provides access to the native buffer/texture objects and also allows creating Diligent Engine objects from native handles. It allows applications seamlessly integrate native API-specific code with Diligent Engine.
      Next-generation APIs allow fine level-control over how resources are allocated. Diligent Engine does not currently expose this functionality, but it can be added by implementing IResourceAllocator interface that encapsulates specifics of resource allocation and providing this interface to CreateBuffer() or CreateTexture() methods. If null is provided, default allocator should be used.
      Initializing the Pipeline State
      As it was mentioned earlier, Diligent Engine follows next-gen APIs to configure the graphics/compute pipeline. One big Pipelines State Object (PSO) encompasses all required states (all shader stages, input layout description, depth stencil, rasterizer and blend state descriptions etc.). This approach maps directly to Direct3D12/Vulkan, but is also beneficial for older APIs as it eliminates pipeline misconfiguration errors. With many individual calls tweaking various GPU pipeline settings it is very easy to forget to set one of the states or assume the stage is already properly configured when in fact it is not. Using pipeline state object helps avoid these problems as all stages are configured at once.
      Creating Shaders
      While in earlier APIs shaders were bound separately, in the next-generation APIs as well as in Diligent Engine shaders are part of the pipeline state object. The biggest challenge when authoring shaders is that Direct3D and OpenGL/Vulkan use different shader languages (while Apple uses yet another language in their Metal API). Maintaining two versions of every shader is not an option for real applications and Diligent Engine implements shader source code converter that allows shaders authored in HLSL to be translated to GLSL. To create a shader, one needs to populate ShaderCreationAttribs structure. SourceLanguage member of this structure tells the system which language the shader is authored in:
      SHADER_SOURCE_LANGUAGE_DEFAULT - The shader source language matches the underlying graphics API: HLSL for Direct3D11/Direct3D12 mode, and GLSL for OpenGL and OpenGLES modes. SHADER_SOURCE_LANGUAGE_HLSL - The shader source is in HLSL. For OpenGL and OpenGLES modes, the source code will be converted to GLSL. SHADER_SOURCE_LANGUAGE_GLSL - The shader source is in GLSL. There is currently no GLSL to HLSL converter, so this value should only be used for OpenGL and OpenGLES modes. There are two ways to provide the shader source code. The first way is to use Source member. The second way is to provide a file path in FilePath member. Since the engine is entirely decoupled from the platform and the host file system is platform-dependent, the structure exposes pShaderSourceStreamFactory member that is intended to provide the engine access to the file system. If FilePath is provided, shader source factory must also be provided. If the shader source contains any #include directives, the source stream factory will also be used to load these files. The engine provides default implementation for every supported platform that should be sufficient in most cases. Custom implementation can be provided when needed.
      When sampling a texture in a shader, the texture sampler was traditionally specified as separate object that was bound to the pipeline at run time or set as part of the texture object itself. However, in most cases it is known beforehand what kind of sampler will be used in the shader. Next-generation APIs expose new type of sampler called static sampler that can be initialized directly in the pipeline state. Diligent Engine exposes this functionality: when creating a shader, textures can be assigned static samplers. If static sampler is assigned, it will always be used instead of the one initialized in the texture shader resource view. To initialize static samplers, prepare an array of StaticSamplerDesc structures and initialize StaticSamplers and NumStaticSamplers members. Static samplers are more efficient and it is highly recommended to use them whenever possible. On older APIs, static samplers are emulated via generic sampler objects.
      The following is an example of shader initialization:
      ShaderCreationAttribs Attrs; Attrs.Desc.Name = "MyPixelShader"; Attrs.FilePath = "MyShaderFile.fx"; Attrs.SearchDirectories = "shaders;shaders\\inc;"; Attrs.EntryPoint = "MyPixelShader"; Attrs.Desc.ShaderType = SHADER_TYPE_PIXEL; Attrs.SourceLanguage = SHADER_SOURCE_LANGUAGE_HLSL; BasicShaderSourceStreamFactory BasicSSSFactory(Attrs.SearchDirectories); Attrs.pShaderSourceStreamFactory = &BasicSSSFactory; ShaderVariableDesc ShaderVars[] = {     {"g_StaticTexture", SHADER_VARIABLE_TYPE_STATIC},     {"g_MutableTexture", SHADER_VARIABLE_TYPE_MUTABLE},     {"g_DynamicTexture", SHADER_VARIABLE_TYPE_DYNAMIC} }; Attrs.Desc.VariableDesc = ShaderVars; Attrs.Desc.NumVariables = _countof(ShaderVars); Attrs.Desc.DefaultVariableType = SHADER_VARIABLE_TYPE_STATIC; StaticSamplerDesc StaticSampler; StaticSampler.Desc.MinFilter = FILTER_TYPE_LINEAR; StaticSampler.Desc.MagFilter = FILTER_TYPE_LINEAR; StaticSampler.Desc.MipFilter = FILTER_TYPE_LINEAR; StaticSampler.TextureName = "g_MutableTexture"; Attrs.Desc.NumStaticSamplers = 1; Attrs.Desc.StaticSamplers = &StaticSampler; ShaderMacroHelper Macros; Macros.AddShaderMacro("USE_SHADOWS", 1); Macros.AddShaderMacro("NUM_SHADOW_SAMPLES", 4); Macros.Finalize(); Attrs.Macros = Macros; RefCntAutoPtr<IShader> pShader; m_pDevice->CreateShader( Attrs, &pShader );
      Creating the Pipeline State Object
      After all required shaders are created, the rest of the fields of the PipelineStateDesc structure provide depth-stencil, rasterizer, and blend state descriptions, the number and format of render targets, input layout format, etc. For instance, rasterizer state can be described as follows:
      PipelineStateDesc PSODesc; RasterizerStateDesc &RasterizerDesc = PSODesc.GraphicsPipeline.RasterizerDesc; RasterizerDesc.FillMode = FILL_MODE_SOLID; RasterizerDesc.CullMode = CULL_MODE_NONE; RasterizerDesc.FrontCounterClockwise = True; RasterizerDesc.ScissorEnable = True; RasterizerDesc.AntialiasedLineEnable = False; Depth-stencil and blend states are defined in a similar fashion.
      Another important thing that pipeline state object encompasses is the input layout description that defines how inputs to the vertex shader, which is the very first shader stage, should be read from the memory. Input layout may define several vertex streams that contain values of different formats and sizes:
      // Define input layout InputLayoutDesc &Layout = PSODesc.GraphicsPipeline.InputLayout; LayoutElement TextLayoutElems[] = {     LayoutElement( 0, 0, 3, VT_FLOAT32, False ),     LayoutElement( 1, 0, 4, VT_UINT8, True ),     LayoutElement( 2, 0, 2, VT_FLOAT32, False ), }; Layout.LayoutElements = TextLayoutElems; Layout.NumElements = _countof( TextLayoutElems ); Finally, pipeline state defines primitive topology type. When all required members are initialized, a pipeline state object can be created by IRenderDevice::CreatePipelineState() method:
      // Define shader and primitive topology PSODesc.GraphicsPipeline.PrimitiveTopologyType = PRIMITIVE_TOPOLOGY_TYPE_TRIANGLE; PSODesc.GraphicsPipeline.pVS = pVertexShader; PSODesc.GraphicsPipeline.pPS = pPixelShader; PSODesc.Name = "My pipeline state"; m_pDev->CreatePipelineState(PSODesc, &m_pPSO); When PSO object is bound to the pipeline, the engine invokes all API-specific commands to set all states specified by the object. In case of Direct3D12 this maps directly to setting the D3D12 PSO object. In case of Direct3D11, this involves setting individual state objects (such as rasterizer and blend states), shaders, input layout etc. In case of OpenGL, this requires a number of fine-grain state tweaking calls. Diligent Engine keeps track of currently bound states and only calls functions to update these states that have actually changed.
      Binding Shader Resources
      Direct3D11 and OpenGL utilize fine-grain resource binding models, where an application binds individual buffers and textures to certain shader or program resource binding slots. Direct3D12 uses a very different approach, where resource descriptors are grouped into tables, and an application can bind all resources in the table at once by setting the table in the command list. Resource binding model in Diligent Engine is designed to leverage this new method. It introduces a new object called shader resource binding that encapsulates all resource bindings required for all shaders in a certain pipeline state. It also introduces the classification of shader variables based on the frequency of expected change that helps the engine group them into tables under the hood:
      Static variables (SHADER_VARIABLE_TYPE_STATIC) are variables that are expected to be set only once. They may not be changed once a resource is bound to the variable. Such variables are intended to hold global constants such as camera attributes or global light attributes constant buffers. Mutable variables (SHADER_VARIABLE_TYPE_MUTABLE) define resources that are expected to change on a per-material frequency. Examples may include diffuse textures, normal maps etc. Dynamic variables (SHADER_VARIABLE_TYPE_DYNAMIC) are expected to change frequently and randomly. Shader variable type must be specified during shader creation by populating an array of ShaderVariableDesc structures and initializing ShaderCreationAttribs::Desc::VariableDesc and ShaderCreationAttribs::Desc::NumVariables members (see example of shader creation above).
      Static variables cannot be changed once a resource is bound to the variable. They are bound directly to the shader object. For instance, a shadow map texture is not expected to change after it is created, so it can be bound directly to the shader:
      PixelShader->GetShaderVariable( "g_tex2DShadowMap" )->Set( pShadowMapSRV ); Mutable and dynamic variables are bound via a new Shader Resource Binding object (SRB) that is created by the pipeline state (IPipelineState::CreateShaderResourceBinding()):
      m_pPSO->CreateShaderResourceBinding(&m_pSRB); Note that an SRB is only compatible with the pipeline state it was created from. SRB object inherits all static bindings from shaders in the pipeline, but is not allowed to change them.
      Mutable resources can only be set once for every instance of a shader resource binding. Such resources are intended to define specific material properties. For instance, a diffuse texture for a specific material is not expected to change once the material is defined and can be set right after the SRB object has been created:
      m_pSRB->GetVariable(SHADER_TYPE_PIXEL, "tex2DDiffuse")->Set(pDiffuseTexSRV); In some cases it is necessary to bind a new resource to a variable every time a draw command is invoked. Such variables should be labeled as dynamic, which will allow setting them multiple times through the same SRB object:
      m_pSRB->GetVariable(SHADER_TYPE_VERTEX, "cbRandomAttribs")->Set(pRandomAttrsCB); Under the hood, the engine pre-allocates descriptor tables for static and mutable resources when an SRB objcet is created. Space for dynamic resources is dynamically allocated at run time. Static and mutable resources are thus more efficient and should be used whenever possible.
      As you can see, Diligent Engine does not expose low-level details of how resources are bound to shader variables. One reason for this is that these details are very different for various APIs. The other reason is that using low-level binding methods is extremely error-prone: it is very easy to forget to bind some resource, or bind incorrect resource such as bind a buffer to the variable that is in fact a texture, especially during shader development when everything changes fast. Diligent Engine instead relies on shader reflection system to automatically query the list of all shader variables. Grouping variables based on three types mentioned above allows the engine to create optimized layout and take heavy lifting of matching resources to API-specific resource location, register or descriptor in the table.
      This post gives more details about the resource binding model in Diligent Engine.
      Setting the Pipeline State and Committing Shader Resources
      Before any draw or compute command can be invoked, the pipeline state needs to be bound to the context:
      m_pContext->SetPipelineState(m_pPSO); Under the hood, the engine sets the internal PSO object in the command list or calls all the required native API functions to properly configure all pipeline stages.
      The next step is to bind all required shader resources to the GPU pipeline, which is accomplished by IDeviceContext::CommitShaderResources() method:
      m_pContext->CommitShaderResources(m_pSRB, COMMIT_SHADER_RESOURCES_FLAG_TRANSITION_RESOURCES); The method takes a pointer to the shader resource binding object and makes all resources the object holds available for the shaders. In the case of D3D12, this only requires setting appropriate descriptor tables in the command list. For older APIs, this typically requires setting all resources individually.
      Next-generation APIs require the application to track the state of every resource and explicitly inform the system about all state transitions. For instance, if a texture was used as render target before, while the next draw command is going to use it as shader resource, a transition barrier needs to be executed. Diligent Engine does the heavy lifting of state tracking.  When CommitShaderResources() method is called with COMMIT_SHADER_RESOURCES_FLAG_TRANSITION_RESOURCES flag, the engine commits and transitions resources to correct states at the same time. Note that transitioning resources does introduce some overhead. The engine tracks state of every resource and it will not issue the barrier if the state is already correct. But checking resource state is an overhead that can sometimes be avoided. The engine provides IDeviceContext::TransitionShaderResources() method that only transitions resources:
      m_pContext->TransitionShaderResources(m_pPSO, m_pSRB); In some scenarios it is more efficient to transition resources once and then only commit them.
      Invoking Draw Command
      The final step is to set states that are not part of the PSO, such as render targets, vertex and index buffers. Diligent Engine uses Direct3D11-syle API that is translated to other native API calls under the hood:
      ITextureView *pRTVs[] = {m_pRTV}; m_pContext->SetRenderTargets(_countof( pRTVs ), pRTVs, m_pDSV); // Clear render target and depth buffer const float zero[4] = {0, 0, 0, 0}; m_pContext->ClearRenderTarget(nullptr, zero); m_pContext->ClearDepthStencil(nullptr, CLEAR_DEPTH_FLAG, 1.f); // Set vertex and index buffers IBuffer *buffer[] = {m_pVertexBuffer}; Uint32 offsets[] = {0}; Uint32 strides[] = {sizeof(MyVertex)}; m_pContext->SetVertexBuffers(0, 1, buffer, strides, offsets, SET_VERTEX_BUFFERS_FLAG_RESET); m_pContext->SetIndexBuffer(m_pIndexBuffer, 0); Different native APIs use various set of function to execute draw commands depending on command details (if the command is indexed, instanced or both, what offsets in the source buffers are used etc.). For instance, there are 5 draw commands in Direct3D11 and more than 9 commands in OpenGL with something like glDrawElementsInstancedBaseVertexBaseInstance not uncommon. Diligent Engine hides all details with single IDeviceContext::Draw() method that takes takes DrawAttribs structure as an argument. The structure members define all attributes required to perform the command (primitive topology, number of vertices or indices, if draw call is indexed or not, if draw call is instanced or not, if draw call is indirect or not, etc.). For example:
      DrawAttribs attrs; attrs.IsIndexed = true; attrs.IndexType = VT_UINT16; attrs.NumIndices = 36; attrs.Topology = PRIMITIVE_TOPOLOGY_TRIANGLE_LIST; pContext->Draw(attrs); For compute commands, there is IDeviceContext::DispatchCompute() method that takes DispatchComputeAttribs structure that defines compute grid dimension.
      Source Code
      Full engine source code is available on GitHub and is free to use. The repository contains tutorials, sample applications, asteroids performance benchmark and an example Unity project that uses Diligent Engine in native plugin.
      Atmospheric scattering sample demonstrates how Diligent Engine can be used to implement various rendering tasks: loading textures from files, using complex shaders, rendering to multiple render targets, using compute shaders and unordered access views, etc.

      Asteroids performance benchmark is based on this demo developed by Intel. It renders 50,000 unique textured asteroids and allows comparing performance of Direct3D11 and Direct3D12 implementations. Every asteroid is a combination of one of 1000 unique meshes and one of 10 unique textures.

      Finally, there is an example project that shows how Diligent Engine can be integrated with Unity.

      Future Work
      The engine is under active development. It currently supports Windows desktop, Universal Windows, Linux, Android, MacOS, and iOS platforms. Direct3D11, Direct3D12, OpenGL/GLES backends are now feature complete. Vulkan backend is coming next, and Metal backend is in the plan.
    • By LifeArtist
      Good Evening,
      I want to make a 2D game which involves displaying some debug information. Especially for collision, enemy sights and so on ...
      First of I was thinking about all those shapes which I need will need for debugging purposes: circles, rectangles, lines, polygons.
      I am really stucked right now because of the fundamental question:
      Where do I store my vertices positions for each line (object)? Currently I am not using a model matrix because I am using orthographic projection and set the final position within the VBO. That means that if I add a new line I would have to expand the "points" array and re-upload (recall glBufferData) it every time. The other method would be to use a model matrix and a fixed vbo for a line but it would be also messy to exactly create a line from (0,0) to (100,20) calculating the rotation and scale to make it fit.
      If I proceed with option 1 "updating the array each frame" I was thinking of having 4 draw calls every frame for the lines vao, polygons vao and so on. 
      In addition to that I am planning to use some sort of ECS based architecture. So the other question would be:
      Should I treat those debug objects as entities/components?
      For me it would make sense to treat them as entities but that's creates a new issue with the previous array approach because it would have for example a transform and render component. A special render component for debug objects (no texture etc) ... For me the transform component is also just a matrix but how would I then define a line?
      Treating them as components would'nt be a good idea in my eyes because then I would always need an entity. Well entity is just an id !? So maybe its a component?
      Regards,
      LifeArtist
    • By QQemka
      Hello. I am coding a small thingy in my spare time. All i want to achieve is to load a heightmap (as the lowest possible walking terrain), some static meshes (elements of the environment) and a dynamic character (meaning i can move, collide with heightmap/static meshes and hold a varying item in a hand ). Got a bunch of questions, or rather problems i can't find solution to myself. Nearly all are deal with graphics/gpu, not the coding part. My c++ is on high enough level.
      Let's go:
      Heightmap - i obviously want it to be textured, size is hardcoded to 256x256 squares. I can't have one huge texture stretched over entire terrain cause every pixel would be enormous. Thats why i decided to use 2 specified textures. First will be a tileset consisting of 16 square tiles (u v range from 0 to 0.25 for first tile and so on) and second a 256x256 buffer with 0-15 value representing index of the tile from tileset for every heigtmap square. Problem is, how do i blend the edges nicely and make some computationally cheap changes so its not obvious there are only 16 tiles? Is it possible to generate such terrain with some existing program?
      Collisions - i want to use bounding sphere and aabb. But should i store them for a model or entity instance? Meaning i have 20 same trees spawned using the same tree model, but every entity got its own transformation (position, scale etc). Storing collision component per instance grats faster access + is precalculated and transformed (takes additional memory, but who cares?), so i stick with this, right? What should i do if object is dynamically rotated? The aabb is no longer aligned and calculating per vertex min/max everytime object rotates/scales is pretty expensive, right?
      Drawing aabb - problem similar to above (storing aabb data per instance or model). This time in my opinion per model is enough since every instance also does not have own vertex buffer but uses the shared one (so 20 trees share reference to one tree model). So rendering aabb is about taking the model's aabb, transforming with instance matrix and voila. What about aabb vertex buffer (this is more of a cosmetic question, just curious, bumped onto it in time of writing this). Is it better to make it as 8 points and index buffer (12 lines), or only 2 vertices with min/max x/y/z and having the shaders dynamically generate 6 other vertices and draw the box? Or maybe there should be just ONE 1x1x1 cube box template moved/scaled per entity?
      What if one model got a diffuse texture and a normal map, and other has only diffuse? Should i pass some bool flag to shader with that info, or just assume that my game supports only diffuse maps without fancy stuff?
      There were several more but i forgot/solved them at time of writing
      Thanks in advance
  • Advertisement