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OpenGL Addiction to OpenGL breaks me up.

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Hi guys, I am an OpenGL addict. That is a fact. Thus, when I started writing my first engine tests, I used OpenGL, which works fine. But now, with my next experimental engine I chose Direct3D because I wanted to use several specific D3D features and I wanted to overcome some problems. But, as an addict, you can''t stop with your drug. So, maybe you guys can help me with OpenGL equivalents of the specific D3D features I needed. - Support for VoodooXX cards. Just using M$ OpenGL32.DLL does not work on those cards. Is there a generic way to overcome this? - Rendering into a texture. For my shadow algorithm I need to render into a 128x128 or so texture as the first pass, and then use that texture in the second rendering pass. - The use of S3TC/DXTC/WhateverTC. This allows me to use larger textures, and render quicker. (ever used 1024x1024 textures? They are s-l-o-w) - This one is probably not possible: Using the ELSA Revelator shutter glasses or another shutter glass system. - Use hardware bumpmapping, if available. - Information about the amount of available hardware texture memory, so I can decide myself when and where to swap in/out textures. - Fast texture updates between frames (animated textures) Thanks in advance, DaBit

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Now I''ve never used either OpenGL or Direct3D before (gave up, still learning DDraw and suchlike), but...

Maybe with the animated textures, it would be easier to have your animation all loaded onto the hardware at once, then just go into the pointer to a texture in your whatever object and change it to the next one.

Just an idea

-Ben Dilts

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Yes, a good idea, but not always feasible, since sometimes I want to regenerate textures, so I can''t pre-load them. With DirectX I exactly know what format my (texture)surface is, so I can choose manually between a 5:6:5, 5:5:5, 8:8:8 or generic (x:x:x) routine. With OpenGL, all I can do is tell the driver to use a 24-bit texture and doing a glTexImage2D with 24-bit RGB triples, and hope the driver won''t get in the way.

The same is true with texture management. In my 3D engine I know exactly which textures I need, which I am going to need within a few frames, and which I won''t need for a longer time. A method to do manual paging, or at least query how much video memory is available for textures would be very handy for this stuff. I know there is such a thing as texture priorization, but this is not quite what I need.

On nVidia cards this works pretty well, but their OpenGL driver is of a rarely seen high quality. And I don''t want to write software that runs only well on nVidia hardware.

DaBit.

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Guest Anonymous Poster
It seems you do not have sufficient experience on OpenGL, especially latest one.

OpenGL hardware bump mapping is now supported by more cards than Direct3D: Geforce and ATI rage128/Pro all support OpenGL hardware bump mapping. Only Matrix400 supports Direct3D bump mapping, Direct3D bump mapping demo freezeswith other video cards.

As for S3TC, OpenGL has virtual texturing technology which is better than S3TC.

Texture animations are very easy. You should buy Nehe code example. Voodoo Cards are now supported by using 3dfx ICD.

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I do have OpenGL experience on both Linux and Windows. I have build a 3D engine testbench with it (see http://dabit.trybit.com, then Dabit3D. There is an (pretty old) sample of it over there.), so I am comfortable with the usual OpenGL stuff like texturing, display lists, (compiled) vertex arrays and the like. It is true that except the compiled vertex array and ARB_multitexture extensions, I did not pay too much attention to the other extensions since I have no idea which extensions are fairly common. But it seems that you are experienced, thus please help me out with those problems.

During the development of my 3D engine test, I encountered a lot of problems, like the VoodooXX support. Just binding the app to OpenGL32.DLL does not work, for some reasons. And I do not want to import a 3DFXGL.DLL myself or use other nasty tricks to get things working on 3DFX cards.
Is this problem solved already for the V2, Banshee and V3??

About OpenGL virtual texturing being better than S3TC, these are two completely different techniques, and cannot be compared against each other. S3TC (DXTC) and FXTC store a texture using less bits, even down to 2 bits per RGB texel. This allows for larger, more detailed textures in the same amount of texture memory. OpenGL virtual texturing just swaps textures in and out of video memory.

The comparison of OpenGL''s texture manager with D3D''s texturemanager is a better one. And yes, in this case OpenGL wins hands down from Direct3D (version 6.1 at least). But with D3D I have the choice to use the builtin texture manager or do it myself. With OpenGL I don''t have that choice. When using a lot of textures in a scene, being able to do texturemanagement yourself pays off since you know when to swap what texture based on your scene graph, and OpenGL doesn''t. Knowing how much (fast) video memory is available would help, so I can create, delete and prioritize textures according to this information instead of throwing it all to OpenGL and let the driver sort it out. BTW, this is also a complaint of Tim Sweeney (Epic Games) against OpenGL, and the main reason why Unreal Tournament runs way better using the DirectX driver than the OpenGL driver on cards with less than 32Mb of local memory.

About texture animations, I will take a look at NeHe''s samples.

Another big problem for me is rendering to a texture. How would I do that quickly? I am aware of the fact that I can render to the backbuffer and using glCopyTexImage2D to transfer the image data to the texture. However, this is slow.

Anyway, thenks for your answer.

DaBit.


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Addiction to Direct3D will break you up.

Microsoft offer of Windows open source code was rejected at court. The only way to settle down this monopoly issue seems to break up Microsoft.

Kate

Edited by - kate on 3/16/00 9:39:27 AM

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Wanna use opengl with a 3dfx card huh? I can relate. In fact my first 3d accelerator was a Voodoo2 and the whole reason I learned OpenGL was to code cool stuff for it after I first played accelerated Quake 2!

Now that 3dfx has finally released an OpenGL ICD, it''s fairly easy. Get the Quake 3 compatible 3dfxvgl.dll and put it in your program''s dir, but rename it opengl32.dll. You can link your program to the standard opengl32.lib. Make sure you put your window at 0,0 and size it to the display es. Also configure the windows display resolution settings before greating your gl window!

Upon execution your program should load the 3dfx gl dll which will automatically go into fullscreen on the gl card.

Note that using glu/glut/glaux libraries may cause problems. For best results you should stick to using what''s in the bare bones gl lib.

I strongly suggest that you do learn to import the dll manually, though. When you do you can do many cool things such as hiding the 3dfx "splash screen" when your program starts and you can change resolution while your program is running. If you use the aforementioned method it will be slightly easier to write your code but you lose this extra functionality.

Microsoft offered to open source Windoze? I wonder if they were going to take out all the code that spies on the users of MS software and gathers info illegally first? Hey maybe I could finally discover what the NSA is checking out about me! :D

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Let''s see:

- Anything post voodoo2 has a real installable driver. Anything before that, you just have to use the miniGLs. There''s no getting around that because of the way 3dfx designed the cards and microsoft implemented opengl in windows.

Although as stated above, dynamically linking the dll is a good move, even if you''re not using a 3dfx card. See Ryan Haksi''s page for code to detect the 3dfx minigl and dynamically load it or the default dll:

http://members.home.com/borealis/opengl.html

- You can render to a buffer and create a texture out of that, but it''s not supported well in drivers. Again, this is because microsoft chose not to implement it the right way.

- S3TC is supported in opengl as an extension. I still need to write an article about that.

- I have no idea about shutter glasses support. It''s a driver issue as far as I know. There is support in OpenGL for stereo rendering, but it''s up to microsoft and the hardware vendors to support it.

- Depends on the type of bumpmapping. If you mean evironment-mapped-bump-mapping from Matrox, I don''t think they''ve implemented an extension in opengl yet. They told me they were planning on it last summer bofore the g400 came out, but I haven''t heard anything else about it since.

Other bump mapping techniques are supported in hardware. I''m not sure what the extensions are though. You''d have to check with the vendors.

- In OpenGL the texture management is done in the driver. That''s the just model it uses. While you can implement your own texture manager (Tim Sweeney did for UT) you can, but for the most part, the driver writers do a pretty good job.

- I have an article on procedural textures. You don''t get direct access to texture memory (do you get that in directx?), but glSubTexImage2d and even glTexImage2d are both pretty quick on recent video cards.

Here''s the official opengl extension registry which may help:
http://oss.sgi.com/projects/ogl-sample/registry/


hope this helps...

Scott Franke [druid-]
sfranke@usc.edu
druid-'s GL Journal
http://www.gamedev.net/opengl

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Oh, here''s the link to my procedural texture article:

http://www.gamedev.net/opengl/proctex.html

You''ll need to download the source to my ambient psychosis demo to get any code:

http://www.gamedev.net/opengl/ambient.html


and as far as virtual texturing, that''s only in the 3dLabs Permedia3 as far as I know.



Scott Franke [druid-]
sfranke@usc.edu
druid-'s GL Journal
http://www.gamedev.net/opengl

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Druid, thanks a lot.

I will have a look at your samples, and download the dynamic OpenGL DLL loading code. The problem of not being to able to render to a texture quickly might be the biggest of them all. (Yes, you can get direct access to video RAM with D3D) With D3D I just create a rendering context to my texture, and that works pretty well as long as I don''t need Z-buffering.

I doubt if I still have valid reasons to use D3D. Oh well, one. The extensive texture combine operators when doing multitexturing. (with modulate_2X and add being the two most useful additions to normal modulation)
There is an extension to allow other texel combination parameters than only GL_REPLACE, GL_DECAL and GL_MODULATE. Is it widely supported?

Is there a list of extensions which indicates what hardware supports it?

DaBit.

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Druid, thanks again.
That table was just what I was looking for. This allows me to choose the extensions to support.

Do you know which extension provides other modulation between textures in a multitexture environment than the standard GL_MODULATE, GL_DECAL and GL_REPLACE? (thus the blend mode between texture units, not between multiple passes)

I also ran your exttest program with the 5.08 Detonator drivers in Win98 on a GeForce DDR (Creative Annihilator Pro). These drivers provide more extensions than you mention for the GeForce. And, jippieyahoo!, also S3TC is supported (GL_S3_s3tc)

I have to post them here since at the moment I can''t send E-mail. I know a message board should not be used for this, thus excuses in advance for that. (also to the moderator)

druid-''s GLinfo v1.0
OpenGL driver info:
Vendor: NVIDIA Corporation
Renderer: GeForce 256/AGP/3DNOW!

Extensions:
GL_ARB_multitexture
GL_ARB_texture_cube_map
GL_ARB_texture_env_add
GL_ARB_transpose_matrix
GL_EXT_abgr GL_EXT_bgra
GL_EXT_blend_color
GL_EXT_blend_minmax
GL_EXT_blend_subtract
GL_EXT_compiled_vertex_array
GL_EXT_fog_coord
GL_EXT_packed_pixels
GL_EXT_paletted_texture
GL_EXT_point_parameters
GL_EXT_rescale_normal
GL_EXT_secondary_color
GL_EXT_separate_specular_color GL_EXT_shared_texture_palette
GL_EXT_stencil_wrap
GL_EXT_texture_edge_clamp
GL_EXT_texture_env_add
GL_EXT_texture_env_combine
GL_EXT_texture_cube_map
GL_EXT_texture_filter_anisotropic
GL_EXT_texture_lod
GL_EXT_texture_lod_bias
GL_EXT_texture_object
GL_EXT_vertex_array
GL_EXT_vertex_weighting
GL_KTX_buffer_region
GL_NV_blend_square
GL_NV_fog_distance
GL_NV_light_max_exponent
GL_NV_register_combiners
GL_NV_texgen_emboss
GL_NV_texgen_reflection
GL_NV_texture_env_combine4
GL_NV_vertex_array_range
GL_S3_s3tc
GL_SGIS_multitexture
GL_SGIS_texture_lod
GL_WIN_swap_hint
WGL_EXT_swap_control



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Druid, thanks again.
That table was just what I was looking for. This allows me to choose the extensions to support.

Do you know which extension provides other modulation between textures in a multitexture environment than the standard GL_MODULATE, GL_DECAL and GL_REPLACE? (thus the blend mode between texture units, not between multiple passes)

I also ran your exttest program with the 5.08 Detonator drivers in Win98 on a GeForce DDR (Creative Annihilator Pro). These drivers provide more extensions than you mention for the GeForce. And, jippieyahoo!, also S3TC is supported (GL_S3_s3tc)

I have to post them here since at the moment I can''t send E-mail. I know a message board should not be used for this, thus excuses in advance for that. (also to the moderator)

druid-''s GLinfo v1.0
OpenGL driver info:
Vendor: NVIDIA Corporation
Renderer: GeForce 256/AGP/3DNOW!

Extensions:
GL_ARB_multitexture
GL_ARB_texture_cube_map
GL_ARB_texture_env_add
GL_ARB_transpose_matrix
GL_EXT_abgr GL_EXT_bgra
GL_EXT_blend_color
GL_EXT_blend_minmax
GL_EXT_blend_subtract
GL_EXT_compiled_vertex_array
GL_EXT_fog_coord
GL_EXT_packed_pixels
GL_EXT_paletted_texture
GL_EXT_point_parameters
GL_EXT_rescale_normal
GL_EXT_secondary_color
GL_EXT_separate_specular_color GL_EXT_shared_texture_palette
GL_EXT_stencil_wrap
GL_EXT_texture_edge_clamp
GL_EXT_texture_env_add
GL_EXT_texture_env_combine
GL_EXT_texture_cube_map
GL_EXT_texture_filter_anisotropic
GL_EXT_texture_lod
GL_EXT_texture_lod_bias
GL_EXT_texture_object
GL_EXT_vertex_array
GL_EXT_vertex_weighting
GL_KTX_buffer_region
GL_NV_blend_square
GL_NV_fog_distance
GL_NV_light_max_exponent
GL_NV_register_combiners
GL_NV_texgen_emboss
GL_NV_texgen_reflection
GL_NV_texture_env_combine4
GL_NV_vertex_array_range
GL_S3_s3tc
GL_SGIS_multitexture
GL_SGIS_texture_lod
GL_WIN_swap_hint
WGL_EXT_swap_control



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      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.
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