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Should a game engine support both OpenGL and DirectX? If it's 'better' to support them both, then why? OpenGL is cross platform, why not only use that one? Thanks in advance, Kees

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Some features are available on one platform or the other at different times. For example, HLSL was available a for a while before GLSL was introduced. Also, not all programmers know both api's, so it might extend your possible user base.

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Original post by Kees Waagmeester
OpenGL is cross platform, why not only use that one?


I can't speak for all people, but OGL is a pain to use compared to D3D when you start doing anything remotely serious.

As for supporting both OGL and D3D, it's something to keep in mind when desiging, maybe abstract your renderer, but it's not terribly important in this day and age. Hell, neither HL2 nor Doom 3 bothered.

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If you're designing your engine to be competitive with other free engines like OGRE, then *maybe* supporting both is a good idea...

Otherwise, IMO there's really no point in supporting both. Then the decision boils down to, cross platform or not? If cross platform, then OpenGL, else DirectX. Keep it simple :)

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OpenGL is available on platforms other than Windows; DirectX is not.

DirectX has better hardware compatibility among off-brand Windows hardware -- which has something like 20% of the market. If you want to run on hardware that's not from NVIDIA, ATI or Intel, you're likely better off with DirectX on Windows.

Thus, you need both if you want maximal coverage.

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Original post by _the_phantom_
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Original post by Promit
I can't speak for all people, but OGL is a pain to use compared to D3D when you start doing anything remotely serious.


why?


Mainly the lack of anything comparable to D3DX. Rewriting the D3DX math routines alone is a pain. Then you have to do normal and tangent computations yourself, as well as pulling in libraries like Cg if you want to have a reasonable material/shader system without writing long, long custom code.

In addition, the OpenGL API is starting to fall apart. It's kind of hit the edge of its scalability, so things are now getting progressively more annoying. You'll want a example, of course:

glActiveTexture( GL_TEXTURE0 );
glEnable( GL_TEXTURE_2D );
glBindTexture( GL_TEXTURE_2D, TexIndex );
glTexEnvi( GL_TEXTURE_ENV, GL_TEXTURE_ENV_MODE, GL_COMBINE );
glTexEnvi( GL_TEXTURE_ENV, GL_SOURCE0_RGB, GL_PRIMARY_COLOR );
glTexEnvi( GL_TEXTURE_ENV, GL_OPERAND0_RGB, GL_SRC_COLOR );
glTexEnvi( GL_TEXTURE_ENV, GL_SOURCE1_RGB, GL_TEXTURE );
glTexEnvi( GL_TEXTURE_ENV, GL_OPERAND1_RGB, GL_SRC_COLOR );
glTexEnvi( GL_TEXTURE_ENV, GL_COMBINE_RGB, GL_DOT3_RGB );

glActiveTexture( GL_TEXTURE1 );
glEnable( GL_TEXTURE_2D );
glBindTexture( GL_TEXTURE_2D, TexIndex2 );
glTexEnvi( GL_TEXTURE_ENV, GL_TEXTURE_ENV_MODE, GL_COMBINE );
glTexEnvi( GL_TEXTURE_ENV, GL_SOURCE0_RGB, GL_CURRENT );
glTexEnvi( GL_TEXTURE_ENV, GL_OPERAND0_RGB, GL_SRC_COLOR );
glTexEnvi( GL_TEXTURE_ENV, GL_SOURCE1_RGB, GL_TEXTURE );
glTexEnvi( GL_TEXTURE_ENV, GL_OPERAND1_RGB, GL_SRC_COLOR );
glTexEnvi( GL_TEXTURE_ENV, GL_COMBINE_RGB, GL_MODULATE );



All that just to set up the stages for two textures. You can do it in about 1/3 as many lines in D3D. There's so many dumb things here. The need to enable GL_TEXTURE_2D. The constant repetition of GL_TEXTURE_ENV for a function that is called glTexEnv. The inability to modify more than one portion of a 6 argument expression at a time. The need to set an active texture, instead of specifying the affected stage for each call. The need to explicitly enable GL_ARB_texture_env_combine. It's just a royal pain.

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The whole DX stinks. Thank god for alternatives. That about sums up the whole DX programming experience for you. I have no idea what I saw in DX in the first place. If you can please use opengl/openal to save yourself some sanity. How can a company that wrote vc6 which I love turn around and produce a dud that DX is? It's like the two aren't even from the same company. Really strange.

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Quote:
Original post by JD
The whole DX stinks. Thank god for alternatives. That about sums up the whole DX programming experience for you. I have no idea what I saw in DX in the first place. If you can please use opengl/openal to save yourself some sanity. How can a company that wrote vc6 which I love turn around and produce a dud that DX is? It's like the two aren't even from the same company. Really strange.


Do you have any justification for your argument? Because I assume DirectX doesn't actually smell. Lots of people use DirectX and are happy with it, so throwing that comment in isn't very helpful for someone unfamiliar with DirectX :)

In my experience, it's really nice to abstract the rendering so you can support both OpenGL and DirectX, but assuming you're making a game in your spare time, there's a lot to be said for just picking one and getting the game done. It's cool to have a decent engine design, but what good's an engine design if you never finish anything?

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I currently spent the last two months learnign both Direct3D and OpenGL.

I had never touched them before.

With each I made a small renderer and a game prototype.

As far as each go IMO, they are equally capabable. But OpenGL is UGLY (im talking about the language, and the source you produce). It just begs for you to write wrappers for the whole thing.

OpenGL is clumsy and even though it has extensive documentation its not always easy to find.

DirectX is pretty (just as pretty as C++) and if you can read you can make it work.

As far as what to put in an engine. To me it seems like that is determined by what sort of developer you want to be.

If you are an indie developer then go cross-platform and do OpenGL. You'll probably find a better market on Mac and Linux desktops, as they are not saturated with games.

IF you want to make huge commercial games, then I'd say go with DirectX. Possibly for the single reason that huge games are complex, and you can cut the complexity level of design and implementation if you go ahead and cut out supporting multiple platforms and many driver configs. Sadly the easiest way to do that would be stick with MS and DirectX.

As well Direct3d and OpenGl comparision is one thing. But there is virtually nothing to compare to DirectX (direct3d, DirectSound/Music, DirectInput, DirectPlay).

OpenAL seemed great. I messed around with SDL but didnt like it too much, leaving me wishing for DirectInput. I'm not sure what a good cross-platform input library is that supports, any joystick, keyboard layout etc..



Just my 2 cents...

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Original post by hplus0603
Thus, you need both if you want maximal coverage.


So if I understand it correctly the reason to implement both is hardware coverage? Or are there other reasons?

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Well, I've never liked DirectX... I don't know.
I found that it produced clumpsy code...
And I had the greatest problems trying to compile a basic example.


But the API that you want to use depends mostly on your target platform and your personal favourite.

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Original post by HAM
OpenGL is clumsy and even though it has extensive documentation its not always easy to find.

DirectX is pretty (just as pretty as C++) and if you can read you can make it work


Really? I'm a C++ man and I find OpenGL far more "pretty". Though, granted I haven't really looked at DX since version 7/8.

Quote:

All that just to set up the stages for two textures.

One thing I like about OpenGL, is that it seems to be closer to the metal as it were. Talking DX7 level of things now, D3D's texture stages have no relevance on how things actually work.

Quote:

Mainly the lack of anything comparable to D3DX. Rewriting the D3DX math routines alone is a pain. Then you have to do normal and tangent computations yourself, as well as pulling in libraries like Cg if you want to have a reasonable material/shader system without writing long, long custom code.


This actually doesn't bother me, which is strange. I've written my own math routines without much problem ( it's not like it's hard in the first place ). If you don't like Cg, there's always GLSL. If you mean something like the .fx format... Then yeah it is quite a hassle to write your own ( I did - took a while ).

One thing I actually like about OpenGL is the extension system, I think it's just grown on me, or I've just become used to it.

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One thing not mentioned so far is the attrictivness (sp?) to employers of being able to use, and showing your use, of more than one API. The majority of game studios that cover more than one platform will use, to a varying degree, their own custom built API.

By showing an employer you are not trapped in one API, and can produce the same outcome with what ever tools you are given is a real plus.

But, and heres my two pence, if your just doing this as a hobby, stick with one for now, you can always abstract the rendering code out later if you want to support more than one API. Want to work on Linux, use OpenGL, windows only, up to you.

I personally have used both, I prefer DirectX simply because I taught myself DX, whereas we had a crappy lecturer at university teaching us OpenGL, and i think that tainted me a bit...

Hope that helps a little
Spree

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It's always cool to see the heated discussion of which is better DirectX or OpenGL.
But the problem is that it is a question of personal taste, and so the discussion is endless.

What I want to discuss is: Use DirectX OR OpenGL in your engine (implement just ONE) or use DirectX AND OpenGL in your engine (implement BOTH).
And how to rectify the (huge) amount of extra work of implementing them both.

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It could possibly be done through a plugin system.
Like you have 2 DDL's (I assume you are making this for the Windows platform, since DirectX is native to Windows). Both have the same routines you can call.

Like Vertex(), Begin(), End(), etc, etc (I know, I know OpenGL syntax, just the lack of knowledge of the DX syntax)...

So you dynamicly link the API you want to use through LoadLibrary function and use the object ot call those functions.

Then those functions do (say for the OpenGL.dll):
void Vertex(...)
{
glVertex3d(...);
}
etc, etc...

Then possibly it's possible to extend your renderer with new API's (I'm 99.9% sure I'm going to learn OpenRT when I can).

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I am basically doing what mldaalder suggested.

I have a CRenderer interface that describes the basic functionality of a renderer. Then I use class inheritance to buidl a DX renderer and an OpenGL renderer.

I use DLL's so that I can in the future switch between renderers and have everything work. At the moment I am working on the DX side of things since that is what I am most familiar with and will then move to openGL later.

To make this all work though I had to basically extract out the abstract ideas about rendering such as texture stages and different operations that could be applied to them so that the renderers can massage the information into the format they like.

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Quote:
Original post by JD
The whole DX stinks. Thank god for alternatives. That about sums up the whole DX programming experience for you. I have no idea what I saw in DX in the first place. If you can please use opengl/openal to save yourself some sanity. How can a company that wrote vc6 which I love turn around and produce a dud that DX is? It's like the two aren't even from the same company. Really strange.

If over 90% of the industry didn't use DirectX and the API was so well designed I might actually agree with you on that idiotic point :) It is also funny you say that as in the latest versions DX has borrowed a lot of ideas and design issues from GL.

Both GL and DX have their place, the only bad point with GL that I have noticed over the years is that games that have been released that aren't by ID users have a harder time playing, etc. A lot of users don't update their drivers every week or two, and I noticed a lot more support issues with GL games versus DX when it came down to drivers.

Obviously that really has nothing to do with GL as an API, but with driver support from manufacturers which I myself count as just as important.

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Original post by python_regious
Quote:

All that just to set up the stages for two textures.

One thing I like about OpenGL, is that it seems to be closer to the metal as it were. Talking DX7 level of things now, D3D's texture stages have no relevance on how things actually work.


I haven't used DX7, but in DX8 and DX9, the texture stages work identically to OpenGL...but the actual syntax is cleaner, less function calls, etc.

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Original post by Promit
...In addition, the OpenGL API is starting to fall apart. It's kind of hit the edge of its scalability, so things are now getting progressively more annoying. You'll want a example, of course:
*** Source Snippet Removed ***
All that just to set up the stages for two textures. You can do it in about 1/3 as many lines in D3D. There's so many dumb things here. The need to enable GL_TEXTURE_2D. The constant repetition of GL_TEXTURE_ENV for a function that is called glTexEnv. The inability to modify more than one portion of a 6 argument expression at a time. The need to set an active texture, instead of specifying the affected stage for each call. The need to explicitly enable GL_ARB_texture_env_combine. It's just a royal pain.


You can just write a little wrapper function with no more than 5 parameters that sets all this up and is more than enough for most cases. For example GL_SetTexCombiner(src0,op0,src1,op1,combine). It's very easy and takes literally no time to write such functions.

As for the original question, I believe an engine should be always as much indepedent as possible from the rendering API, even if it is going to support only one in the end. If you can write rendering ports for both APIs, this is the best solution.

Quote:

...And how to rectify the (huge) amount of extra work of implementing them both.


Huge? Not at all. Compared to the rest of the rendering engine, the API calls are an extremely tiny part of it. In all seriousness, I don't think it would take more than a couple of weeks(and I think I'm being pessimistic here) to write an API port, provided of course the programmer is good at it. Both APIs do pretty much the same things, they just have different syntax.

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Hi everybody,

A) First, before everything: there is no interst in coding an engine if it doesn't hide implementation details, and I believe that the underlaying APIs are implementation details.

B) 3 examples:

B.1) the user wants to create a game. He instanciates the engine, use its neat interface to display what he wants and so on. He don't have to know what is the underlying graphic API. Whether it is DX or gl is not his problem.

B.2) your engine only focus on a specific part of the game - for example, you built a terrain engine. If you want to allow any user to use it (both DX and gl programmers) then you'd better write 2 renderers - one GL and one DX. This will only allow a user to select which one he want to use in the project he is currenlty coding.

B.3) your engine does everything but a particular user wants to add something - say: support for paralax mapping - he'll have to cope with whatever you choosed as the underlying API. Maybe he'll want gl where you put DX. Maybe he'll want DX where you put gl. If you provide 2 rendering API then he'll have to cope with both. He certainly don't want.

As you see, there are different points of view. Choose the one you want depending on what you plan to do.

C) and another question, just for fun: will you change the rasterizer at run time?

D) [conclusion] Remember that the DX vs gl thingy is just a matter of taste for avid gamers. They will choose whatever they want - or worse: they'll choose one for this stupid small 1 fps diff. If you provide 2 underlying rendering API (why not 3 after all? glide still exists. Or 4: you may add a sw rasterizer too), you'll only multiply your work by 2/3/4.

More code = more bugs, more code = more work, more code = more time.

HTH (and hope I stayed on topic ;D ),

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If you provide 2 underlying rendering API (why not 3 after all? glide still exists. Or 4: you may add a sw rasterizer too), you'll only multiply your work by 2/3/4.


The API calls are no more than 10% of the rendering engine, and may I say, an "easy" 10%. So, it's more like multiplying your work by 1.1 rather than 2.

[Edited by - mikeman on January 7, 2005 10:10:59 AM]

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Original post by mikeman
Quote:

If you provide 2 underlying rendering API (why not 3 after all? glide still exists. Or 4: you may add a sw rasterizer too), you'll only multiply your work by 2/3/4.


The API calls are no more than 10% of the rendering engine, and may I say, an "easy" 10%. So, it's more like multiplying your work by 1.1 rather than 2.


If you just replace API calls I'm not sure it will work the same. There is a lot of things to do in order to be able to correctly call a particular API function. Not to mention that since the API philosophy are somewhat different, this may reflect in the code. IMHO the rendering engine itself is a pretty thin layer and most of the rendering engine code deals with the API itself - it is either direct API calls or API call preparation, both of them need to be modified if you implement more than one API.

So you are right, this is probably not a x2, neither it is a x1.1.

Regards,

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Quote:
Original post by Kees Waagmeester
So if I understand it correctly the reason to implement both is hardware coverage?
Yes.

Quote:
Or are there other reasons?
The experience of writing a multi-API renderer, perhaps.

I'm closing this because we've already had one bonehead flame, and I'd expect to see more if I leave it open.

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      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
    • By RenanRR
      Hi All,
      I'm reading the tutorials from learnOpengl site (nice site) and I'm having a question on the camera (https://learnopengl.com/Getting-started/Camera).
      I always saw the camera being manipulated with the lookat, but in tutorial I saw the camera being changed through the MVP arrays, which do not seem to be camera, but rather the scene that changes:
      Vertex Shader:
      #version 330 core layout (location = 0) in vec3 aPos; layout (location = 1) in vec2 aTexCoord; out vec2 TexCoord; uniform mat4 model; uniform mat4 view; uniform mat4 projection; void main() { gl_Position = projection * view * model * vec4(aPos, 1.0f); TexCoord = vec2(aTexCoord.x, aTexCoord.y); } then, the matrix manipulated:
      ..... glm::mat4 projection = glm::perspective(glm::radians(fov), (float)SCR_WIDTH / (float)SCR_HEIGHT, 0.1f, 100.0f); ourShader.setMat4("projection", projection); .... glm::mat4 view = glm::lookAt(cameraPos, cameraPos + cameraFront, cameraUp); ourShader.setMat4("view", view); .... model = glm::rotate(model, glm::radians(angle), glm::vec3(1.0f, 0.3f, 0.5f)); ourShader.setMat4("model", model);  
      So, some doubts:
      - Why use it like that?
      - Is it okay to manipulate the camera that way?
      -in this way, are not the vertex's positions that changes instead of the camera?
      - I need to pass MVP to all shaders of object in my scenes ?
       
      What it seems, is that the camera stands still and the scenery that changes...
      it's right?
       
       
      Thank you
       
    • By dpadam450
      Sampling a floating point texture where the alpha channel holds 4-bytes of packed data into the float. I don't know how to cast the raw memory to treat it as an integer so I can perform bit-shifting operations.

      int rgbValue = int(textureSample.w);//4 bytes of data packed as color
      // algorithm might not be correct and endianness might need switching.
      vec3 extractedData = vec3(  rgbValue & 0xFF000000,  (rgbValue << 8) & 0xFF000000, (rgbValue << 16) & 0xFF000000);
      extractedData /= 255.0f;
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