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OpenGL Can you mix OpenGL with Direct X?

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I was wondering if you could write pieces of a game in OpenGL, and others in Direct X. I''m involved in a project with another programmer- who is learning Direct X while I''m learning OpenGL... is this a problem? Programming::~Fredric(const Annoy_Ance)

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Guest Anonymous Poster
Yes and no. As long as you don''t try to mix oGL with Direct3D or DirectDraw it will work fine.

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?? So, OpenGL DDRAW AND D3D don''t go at all? damn

Programming::~Fredric(const Annoy_Ance)

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Nope. It''s one or the other. When you''re dealing with matters of graphics, you can only really have one API working at a time. If its claimed by OpenGL, there is no room for graphical DirectX, and vice versa. The way they work is VERY different, and they do not mesh well - at all.

However, not all is lost; all non-graphical aspects of DirectX, such as DirectInput and DirectSound and DirectPlay and so on will work fine with OpenGL.

You''re just going to have to make a decision about what your goals are, what you will be able to do with what you know, as well as your desired platform. If its 2D only, I advice DirectDraw; if its 3D, I advise OpenGL. Either way, good luck, and pursue it to no limit. Naturally, it''s best to know both graphical DX AND OpenGL.

- Hai, watashi no chichi no kuruma ga oishii deshita!
...or, in other words, "Yes, my dad's car was deliscious!"

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Thank you for your advice... I''m not sure whether to learn DX or OpenGL, but could someone explain to me why OpenGL is not as good at 2d as DDraw? I heard that you need to learn VC++ for Direct X... that''s mainly why I chose OpenGL in the first place, because I hate VC++! So confusing with all those handles and stuff! Anyhow, can someone help me out?

Programming::~Fredric(const Annoy_Ance)

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maybe you could make 2 versions of what you''re working on. one for OGL and one for DX. it may be extra work, but hey, why not?

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One of the reasons OpenGL isn''t as effective for 2D as DirectDraw is that OpenGL, regardless of what you''re doing, is always running 3D (when you want 2D, you just specify an orthographic projection, but OpenGL still behaves as though you''re specifying things in 3 dimensions). I suppose OpenGL does have various commands for pushing raw pixel data to the framebuffer, but I''m a little uncertain as to just how accelerated that is compared to blitting in DirectDraw. OpenGL was designed more for rendering primitives and the like, while DirectDraw was specifically designed for slapping bitmaps around in video memory.

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direct x 2d graphics look way better than open gl 2d graphics. i''ve been working on both, got 2d working in both of them, and the ogl version of my graphic is dithered, somewhat. however, i''m deciding on using opengl because the codes much easier, and my game is mainly in 3d, so the player won''t have time to pay too much attn to dithered 2d. i''ve been trying to integrate 3d models with 2d graphics (i.e. cockpit in sim) for a while, and i finally got it goin in open gl. direct x, i can just not get direct 3d up and running (via loading x files). bottom line: opengl 3d is as good as ddraw, opengl 2d sucks crap like d3d, but at least i can get it up and running.

a2k

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Direct x is mainly for VC++. However in version 7 there is some stuff for visual basic as well, although, i believe they are little bit slower. If you are new the graphics programming / geometry environment, i woudl definately recommend starting with OPENGL. Direct X is difficult because of the cryptic way it works for beginners, or novices. Opengl hides alot of the hardcore stuff , but does allow one to access that if needed> and makes it a lot easier. John McCormack, Creator of Quake, went from direct x to OpenGl becuase of its ease of use. in the memo he wrote, he stated :" Remember if you are use an API to write a game you will be working with it alot. Therefore make sure its something you''re comfortble with" .

OpenGL is able to do things in a few lines of code that takes DX quite a bit more code to do. There is no speed difference between them that i have noticed. However, remember OpenGL is not the world''s most compatible API. It was designed on a SGI machine, and ported to use 3d Accelerated cards. For the few people who dont have 3d Accelerated cards in their machines, it may run very very slow. and different cards have different effects on OpenGL. Fir instance the older voodoo cards have to be run in 16 bit color mode, or its dog slow. i am not sure about the new ones.

Keep these things in mind when deciding. I had to make the same decision, and ultimately went with OpenGL.

CXI

The Code is a Living breathing entity, and will move in accordance with you, therefore, be one with the Tao of the Code..

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Basically, as long as you don''t mix the rendering aspects everything is OK.

i.e. You can use OpenGL with all DirectX components apart from DDraw & D3D.

On the other question, I am learning OpenGL, I don''t want to start an API war, but I do like it, and so far have found it quite easy to pick up. Although if you don''t like VC++, it might not be a good option.


-Mezz

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Alright, well it looks like I''ll be going with OpenGL purely because it''s easier. However, once I''m done with OpenGL and I have a decent grasp on 3d aspects as well as rendering and that kind of thing, I''ll move on to Direct X. Why move on and learn both? Because it''s just way better to have both.. that way I''ll be able (like a post mentioned above) to make all my games DX and OpenGL compatible. Thanks for all your help, I greatly appreciate it.

Programming::~Fredric(const Annoy_Ance)

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Um, i dont mean to sound rude or like an ass but the creator of Quake was not named John McCormack. His name is John Carmack. Peace.

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yeah, i''m using open gl cuz carmack is. if he wears nike, i''ll wear nike.

a2k

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Guest Anonymous Poster
hmm ... why everyone thinks that opengl is better ? In my opinion, those Draw Primitive stuff in direct3d seems more organised to use than opengl. direct 3d graphics don''t really look that bad and multi-texturing is quite intuitive.

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Man cxi, Voodoo''s are dog slow in anything above 16bit color, so far(until the Voodoo4&5) every 3dfx card only runs in 16BIT COLOR!. Also, when John Carmak was writing that article, He was comparing OpenGL to DirectX5, when you had to use peice of crap Execute Buffers(or whatever,never used em, read bout em). I think that if he compared DirectX7/8 to OpenGl, it would be much closer, though his love for Linux would probaly keep him from saying that.

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I agree with esap1 i first had contact with DirectX 6, and the simplification from 6 to 7 alone was a large step (I cut away a big Part of the initialization, and all this Material and Lighting got much simpler).

Another Thing, why are you all talking about DirectX with VC++, you don''t need Visual C++, you can compile your DirectX Projects with nearly any C-Compiler. I am using Watcom and it works without Problems.

Lars

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Actually, Carmack was comparing OpenGL with DirectX3 -- not 5 (DirectX5 was the first version to introduce DrawPrimitive).

BTW, as for the quality differences between the API''s: there should be none as long as you know what your doing.

--TheGoop

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Actually, Carmack was comparing OpenGL to Direct3D of DirectX 3. Version 5 wasn''t so bad. It added drawprimitive, and thus programmers could avoid using execute buffers.

Direct3D has just gotten better and better. Everyone with common sense agrees that D3D v3 sucked..Some people just tolerated it at the time because the OpenGL driver situation on consumer cards was iffy. Luckily, id took a stand which I believe directly resulted in much better support for OpenGL from vendors and thus more support for OpenGL from other game developers.

In many ways, I think D3D 7 has some slight advantages over OpenGL when it comes to cutting edge features, but I am still using OpenGL for portability reasons. Its nice to run on platforms other than Windows....

Here''s hoping the OpenGL ARB and/or SIGs like Khronos are able to kickstart OpenGL back into the limelight with wider integration of cutting edge extentions, etc.

---

And, to repeat what others have said before me: the answer to your question is that you can mix all of DirectX (including DirectPlay, DInput, DSound, DMusic, etc) with OpenGL as long as you steer clear of D3D or DDraw. There have been rumors for quite some time that Microsoft had an OpenGL32.DLL implementation that could be mixed with DirectDraw, but they never released it because they want to push D3D over OpenGL for gaming. They may release it someday...There IS a PFD_SUPPORT_DIRECTDRAW pixel format flag defined in the newer Microsoft include files for wgl/GDI, but as far as I know it is not generally supported or documented.

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      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
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