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OpenGL Making a GUI system with C++ OpenGL

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All this could sound extremely noob, you have been warned :P. I'd like it to be OO, and of course have it represented in a tree structure. (a window has more windows within it, and those windows can also have more windows, buttons, and all the other widgets). I was thinking it would be nice to give widgets the ability to draw themselves to their parent widget's surface and not to the screenbuffer so that: - if i decide to hide/move the parent, then all of its children will hide/move. - i only have to render them once, until the next time they change or move relative to their parent. - all children share globaly the z position of the parent (but still have an order within that parents children). In other words, the depth of the widgets respects the tree structure. So... seeing what OpenGL has to offer.......... (and asking to be given advice about everithing :P) i can draw raster graphics (glDrawPixels and such) or go the 3d way (textured quads, and i would have a nice way to handle the relative widgets positions, as using opengl's matrixes feels tree-ish enough already :P) The problem is (besides im a noob), i dont know how (or if it is even possible or REASONABLE) to use that to draw to some image data in each widget and not directly to the screenbuffer. Can anybody put some light in this for me? better all around ideas? I did a GUI system that worked very well in DirectorMX2004 drawing with "copypixels", but using OpenGL seems to me like a quite different paradigm than just doing blits to the screen. thanks for reading me :).

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I'd advise against using OpenGL's matrix popping for two reasons;

1. When I used it in the past it wasn't brilliantly fast.

2. You only need translations in 2 dimensions and full matrix stuff seems overkill.

An aggro will start to come with clipping -- when you draw components in X or Win32, the rectangle is a window, and clips the children at its edges. You won't so easily get the clipping if your rectangle is just a rectangle, you'll have to do it yourself and that gets boring rapidly. You could simply ignore this and not do the clipping, but it gets more useful for scrolling lists and similar controls.

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The description of what you want to do seems spot on. Go for it.

If you want to learn how to do it then don't use a 3rd party library, if you want a GUI then do use a 3rd party. My point being there is no better way to learn than to do.

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I am also writing a simple GUI system for use in my own 2D game and when I first started thinking on how to structure it I came up with something similar to your's. My first idea was something like this: I started with a window which had a number of child-windows. These child-windows would be rendered in a OpenGL viewport that was sized and positioned as the parent-window. And windows that were connected to each of these child-windows would be drawn with the viewport of the child's window in turn. That way I wouldn't have to worry about clipping since OGL would handle it for me.

But that meant a lot of calls to glViewport() and glOrtho(). I had to re-position the viewport every time I wanted to draw a child window and I also had to keep track of a number of other things which made me realize that this was not the best way to do it. (It felt like a hack right from the start to be honest. :)

So I decided to clip the windows and widgets myself. What I have now is a class Widget which is essentially a 2D rectangle on the screen. Each widget have a number of child-widgets that are drawn on top of the parent-widget. Each widget also has a number of "primitives" which are the graphical elements that make up the widget. These primitives are then clipped against the viewable area of the widget they belong to. Right now I have 2 types of primitives, lines and boxes which are just lines and quads with a given color. I'm also going to add textured quad- and text primitives when I need them.

When I draw the widgets I start from the top of the tree-structure of widgets and draw each widget's primitives inside the clipping area that I pass along the drawing function. The clipping area covers the whole GUI area to start with then it is calculated by clipping the current clipping area with the widget being drawn. The clipping area is also going to be used to pass input to the right widget.

Clipping rectangles or quads is not that big of a deal. What can be tricky is clipping lines and textured quads.

I hope my ramble could help you in some way or at least give you some ideas. Now I'm off coding the z-sorting. :)

Edit: To answer your question: You could use the glCopyTexImage2D extension to render the child windows to a texture which you then render to screen. Nehe OpenGL tutorial #36

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Quote:
Original post by Redien
You could use the glCopyTexImage2D extension to render the child windows to a texture which you then render to screen. Nehe OpenGL tutorial #36


Another option would be to use OpenGL framebuffer objects (FBOs), which are supposed to be more efficient than drawing and then using glCopyTexImage2D. With FBOs you can draw directly to a texture. FBOs may (?) not be as widely supported:
Framebuffer Objects 101

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When you initialize a frame buffer object, is it the same size as your rendering context (i.e. the size of your window) ? So basically, can it be a non-power of 2 size?

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Quote:
Original post by Redien

... lots of text ...


Why not use glScissor for clipping?

Quote:

The glScissor function defines the scissor box.

void glScissor(
GLint
x,
GLint y,
GLsizei width,
GLsizei height
);

Parameters
x, y
The lower-left corner of the scissor box. Initially (0,0).

width, height
The width and height of the scissor box. When an OpenGL context is first attached to a window, width and height are set to the dimensions of that window.


Remarks
The glScissor function defines a rectangle, called the scissor box, in window coordinates. The first two parameters, x and y, specify the lower-left corner of the box. The width and height parameters specify the width and height of the box.

The scissor test is enabled and disabled using glEnable and glDisable with argument GL_SCISSOR_TEST. While the scissor test is enabled, only pixels that lie within the scissor box can be modified by drawing commands. Window coordinates have integer values at the shared corners of framebuffer pixels, so glScissor(0,0,1,1) allows only the lower-left pixel in the window to be modified, and glScissor(0,0,0,0) disallows modification to all pixels in the window.

When the scissor test is disabled, it is as though the scissor box includes the entire window.

The following functions retrieve information related to glScissor:

glGet with argument GL_SCISSOR_BOX

glIsEnabled with argument GL_SCISSOR_TEST

Error Codes
The following are the error codes generated and their conditions.

GL_INVALID_VALUE either width or height was negative.
GL_INVALID_OPERATION glScissor was called between a call to glBegin and the corresponding call to glEnd.

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Quote:
Original post by ggp83
Why not use glScissor for clipping?


I wasn't aware of that such a function existed. Thanks for the suggestion but I'd still like to do the clipping by hand since I could actually learn something from it and it would keep the OGL state as untouched as possible. :)

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Quote:
Original post by Katie
I'd advise against using OpenGL's matrix popping for two reasons;

1. When I used it in the past it wasn't brilliantly fast.

2. You only need translations in 2 dimensions and full matrix stuff seems overkill.

An aggro will start to come with clipping -- when you draw components in X or Win32, the rectangle is a window, and clips the children at its edges. You won't so easily get the clipping if your rectangle is just a rectangle, you'll have to do it yourself and that gets boring rapidly. You could simply ignore this and not do the clipping, but it gets more useful for scrolling lists and similar controls.


Full matrixes would let you add lots of cool 3D effects, and i don't think it would slow anything down, imho. Of course it would be quite more complicated than keeping it simple, but you can do lots of fancy stuff :). GUIs are a game's first impression and this kind of improvements could add an edge.

Quote:
Original post by nmi
What about using a library that fits your needs:
http://libufo.sourceforge.net/

Maybe you also want to help those people to improve it.


Well, im not against using libs, but right now id like to do this my myself.

Quote:
RedienLots of stuff :P


After i made my post o went on searching for answers (redbook mainly :P) and yes, you helped me put some order to my thougts XD. i had seen the "glScissor" tool in the "redbook" and i was coming happily to tell you, but someone did that already :P.

Quote:
Original post by venzon
Quote:
Original post by Redien
You could use the glCopyTexImage2D extension to render the child windows to a texture which you then render to screen. Nehe OpenGL tutorial #36


Another option would be to use OpenGL framebuffer objects (FBOs), which are supposed to be more efficient than drawing and then using glCopyTexImage2D. With FBOs you can draw directly to a texture. FBOs may (?) not be as widely supported:
Framebuffer Objects 101


Right, i had found exactly that article, and i was wondering if i could actually rely in such extentions for a GUI (provided i probably shouldn't leave the game without a GUI if it is not supported :P).

I'm starting to realize there is no simple answer to my problem. Maybe i should go the glCopyTexImage2D way?

Is there a way to bit a pixelbuffer to another pixelbuffer (and not to de screenbuffer or a texture) so i can then do a glDrawPixels, or something like that? (this is supposing i totally drop the idea of making a 3D GUI).

And i had another idea that may be too crazy (or plain supid XD) to achieve that. If there is no such way, maybe i could have SDL do all those intermediate blits to "surface" objects and just in the end blit the full composition to the opengl screenbuffer.

¿What do you think?

PD: Thanks everyone for your help. :)

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You might want to check out some more libs, just to see how other people have done it.

I have been following guichan [http://guichan.sf.net] development for some time; nicely written code in my opinion. They have both a SDL and an OpenGL backend, so you can see
either way (software blitting and glXXX) in action.

Personally I wouldn't use any extensions in this case, partially because of the need to provide a fallback (if a card doesn't support it) but mainly because the GUI shouldn't cost that many vertices. I like the flexibility that immediate mode (glVertex3f, ...) offers, but that may also be because I lack experience with the newer stuff (my hardware isn't exactly new).

If you really want to blit buffers into buffers SDL_BlitSurface is a good choice; though from what I understood from your first post I don't see why you want to.

If you 'glClear' your screen each frame you have to redraw the complete GUI anyway; and then you don't want to recursively blit buffers (every frame!), so you need some kind of caching. You might want to skip software blitting entirely.

Relative positions and show/hide of children-nodes seem features of your tree & nodes; I don't get why this would require a certain drawing mechanism (blitting).

Best regards,
s

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Quote:
Original post by sunky
You might want to check out some more libs, just to see how other people have done it.

I have been following guichan [http://guichan.sf.net] development for some time; nicely written code in my opinion. They have both a SDL and an OpenGL backend, so you can see
either way (software blitting and glXXX) in action.

Personally I wouldn't use any extensions in this case, partially because of the need to provide a fallback (if a card doesn't support it) but mainly because the GUI shouldn't cost that many vertices. I like the flexibility that immediate mode (glVertex3f, ...) offers, but that may also be because I lack experience with the newer stuff (my hardware isn't exactly new).

If you really want to blit buffers into buffers SDL_BlitSurface is a good choice; though from what I understood from your first post I don't see why you want to.

If you 'glClear' your screen each frame you have to redraw the complete GUI anyway; and then you don't want to recursively blit buffers (every frame!), so you need some kind of caching. You might want to skip software blitting entirely.

Relative positions and show/hide of children-nodes seem features of your tree & nodes; I don't get why this would require a certain drawing mechanism (blitting).

Best regards,
s


agreed about extensions.

about blit, id do that to:
- draw every window component at the right depth, respecting the tree structure, and optionally for clipping.
- to caché al widgets that have not changed relative to their parents.

so if im about to render a new frame, i glClear, then draw the game (optionally), and then draw the GUI on top. If nothing in the GUI tree changed, then the tree's root will have a cache image of exactly what the gui should look like, so i only have to blit that image on top.

Isn't it the way windows work? when you drag a window, all its graphical content is moved as if it were just a graphic, but it is probably composed of maybe 100 controls and buttons. And it is not being completely redrawn, right? Just guessing here.

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Quote:
Original post by sunky
Personally I wouldn't use any extensions in this case, partially because of the need to provide a fallback (if a card doesn't support it) but mainly because the GUI shouldn't cost that many vertices. I like the flexibility that immediate mode (glVertex3f, ...) offers, but that may also be because I lack experience with the newer stuff (my hardware isn't exactly new).

Don’t use the immediate mode. Use display lists or vertex array instead if you want something widely supported. You probably doesn’t need to support OpenGL version older than 1.2. It’s probably better to do things the right way (with VBO) and than provide fallback for hardware that doesn’t support the extension.

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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 two samples, asteroids performance benchmark and example Unity project that uses Diligent Engine in native plugin.
      AntTweakBar sample is Diligent Engine’s “Hello World” example.

       
      Atmospheric scattering sample is a more advanced example. It 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 and Android platforms. Direct3D11, Direct3D12, OpenGL/GLES backends are now feature complete. Vulkan backend is coming next, and support for more platforms is planned.
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