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OpenGL OpenGL in Video Card's memory

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Hello, I am having a problem setting up OpenGL. I need to draw with OpenGL to a memory bitmap. To do that, I need to set the flag PFD_DRAW_TO_BITMAP. While this works, it is not the solution that I need. This is because it renders through the software where the speed is very slow. Unfortunately I need a faster method. I am thinking of drawing to the video card. After some research, I found out that pbuffers and frame buffers can do this. My problem is setting them up. With pbuffers when I would make the context of the bitmap active, as I want to draw the pbuffer onto it, it would fail : a = wglBindTexImageARB(pbuffer.hBuffer, WGL_FRONT_LEFT_ARB); a is always 0. The code works, as if I work directly on a window's HDC, it does not return 0. However, I really need to get it working on the bitmap, as that will probably be my only context. Regarding frame buffers, the same problem occurs. Before making the window active, I use this : MakeCurrentBMP(); glBindFramebufferEXT(GL_FRAMEBUFFER_EXT, 0); Again, the bitmap is returned white, even though I just want to render the cube at the end on the bitmap, with the software. I can provide the source code if it is needed. Can anybody help me ? Are there any examples of what I am trying to do ? Thank you very much in advance.

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If I understand you are trying to:
- render to a texture.
- get the texture to an array in RAM ("memory bitmap")

Render to a texture:

The good method in OpenGL with modern graphic cards is the Frame Buffer Object (FBO). you have to create a new FBO, then attach it to a texture. There is plenty of demos, have a look at that article here at gamedev. Note that you don't need neither Depth texture, nor MRT, just one FBO with a texture attached is enough.


Then you need to get back the texture values (FBO are stored on GPU memory):

- not efficient method is to fetch the values using glGetTexImage
- efficient methods uses the Pixel Buffer Extension (PBO): ReadPixels() to a PBO . Examples could be found at gpgpu for instance (see "fast transfer"): gpgpu

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Hello,

Thank you very much for your help. Here is exactly what I am trying to do :

I already have the HDC to a bitmap in RAM. I need to draw with OpenGL on it. I can use the PFD_DRAW_TO_BITMAP flag, but OpenGL would be run with software support which makes it slow. To get over this, I need to create a pbuffer or FBO.

To create either one of them, I need to initialize an OpenGL window created with the PFD_DRAW_TO_WINDOW tag. I can't do that since I only have a bitmap. I tried initializing a pbuffer and FBO with the PFD_DRAW_TO_BITMAP flag, but it doesn't work, since no extensions can be found, even though I already create the pixel format and context for that bitmap. Yes, I can draw on it with the OpenGL software renderer, it works fine.

To sum this up, I can use glBindFramebufferEXT in my situation.

Maybe I don't need to get as far as drawing on that HDC directly, I think that I can bypass that, I could do that by just getting the RGB values from the video card's memory bitmap.

Here is what I need, just in case I was not clear enough :

I already have a HDC for a bitmap created in system memory.
I need to draw on it with OpenGL.
I need to take advantage of the hardware renderer for speed, as I really need performance. I can draw on it with the software renderer, but it it too slow.
I can not create another window or use another window.

Is there anything that I can do ? Can anybody help me ? Thank you very much in advance.

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Your only choice is to create a window and make it invisible.
Init GL for this window, then create a FBO and render to it. That will give you hw accel. Don't use the backbuffer since that will likely return junk since the window is not visible. Use a FBO!

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Thank you very much for your help. I was able to get it working with a FBO and getting the data from there with glGetTexImage.

I need to blit the data onto a 16 bit bitmap (I have the function to amke it 16 bits from RGB)

Now my problem is blitting the data. With a FBO I can only create it as 512x512 (or smaller, but it must be a power of two). However, my bitmap can have any size ratio, like 300x250. I can draw it bigger and then scale down.

Where should I look for a function or class to do the blitting ? How is this called, is it a special term ? Is there any information about what I am trying to do available ?

I do not want to use the GDI blitter, as it does not work in this example and it is too slow.

Thank you.

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If I understand this correctly and you want to downscale a texture than you could just setup an orthographic projection (glOrtho or gluOrtho2D) and render a quad to the screen:

gluOrtho2D( 0.0, fWidth, 0.0, fHeight );

glBegin( GL_QUADS );
glTexCoord2f( 0.0f, 0.0f ); glVertex2f( 0.0f, 0.0f );
glTexCoord2f( 1.0f, 0.0f ); glVertex2f( fWidth, 0.0f );
glTexCoord2f( 1.0f, 1.0f ); glVertex2f( fWidth, fHeight );
glTexCoord2f( 0.0f, 1.0f ); glVertex2f( 0.0f, fHeight );
glEnd();

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Thanks.

No, I don't want to do that.

I have a bitmap in the RAM. I need to draw on that. If I initialize OpenGL, I only run it in software mode. That is why I create a hidden window and draw in a FBO.

I get the data from the FBO and I need to draw on that bitmap. I can draw on that bitmap easily if I have the RGB colours (and I do, have them). But what I need is a fast blitter. And also one that will take care of the FBO being 512x512 and the bitmap being any ratio. I do this every cycle, that is why it needs to be fast.

I hope that you understand what I am trying to do.

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Well, that's what my previous post should do for you :-). That short snippet is probably the simplest and fastest blitter you can get your hands on in OpenGL. It does two things:

1) It can scale any texture to any size;
2) It can blit any texture onto another texture (the latter being bound to an FBO).

So, if your bitmap is used to input ("blit source"), load it as a texture. It shouldn't matter if you can only use power-of-two (POT) sized bitmaps, when you can downscale them to any non-POT size (and fast). Meaning, if your input is non-POT, resize it offline or at load.

Consequently, if your bitmap is used as an output ("blit destination"), just allocate a texture that is large enough to contain the source (it can be larger!), and strip only that part that you need afterwards. Thus, if you need a 640x480 canvas, allocate the FBO texture/renderbuffer to size 1024x512 and ignore anything else outside the (0,0)-(640,480) viewport.

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Let me explain more about the bitmap.

It is created in RAM memory by a game. I just create a .dll that can access its data. The data is stored in an array at 16bits per pixel. I can not initialize OpenGL on that bitmap as it is in RAM, meaning very slow.

Ok, so I downscale the texture after I draw it in the pbuffer. Then I need to get that data someway out of it and then copy and paste every colour to the location in RAM.

Just getting the data, glReadPixels takes way too much.

glGetTexImage does not work at all :

glBindTexture(GL_TEXTURE_2D, tex);
glGetTexImage(GL_TEXTURE_2D,0,GL_RGB,GL_UNSIGNED_BYTE,text);

Nothing is written to text.

Please let me know if there is a solution to make this work faster as the blitter is not the problem, just the two functions that I just mentioned.

Thanks

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In the case of current gen hardware APIs, there's no fast solution as far as I'm aware. By that I mean that there's a significant cost involved in breaking the optimal flow between CPU and GPU, such as retrieving data from the GPU (such as glReadPixels). This you've already come to know, as it's considered bad practice to access GPU resources from the CPU (and vice versa). Even more so, hardware can't draw to a software framebuffer.

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      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.
    • By michaeldodis
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      Early version of the library
      I'd really love to hear anyone's thoughts on this, any suggestions on what features you'd want to see in a library like this? 
      Thanks in advance!
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