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  • Hash : 8d4331ee
    Author : Shahbaz Youssefi
    Date : 2020-09-16T00:42:08

    Vulkan: Free up 5 bits in RenderPassDesc
    
    Leveraging the fact that there are only a handful of depth/stencil
    formats, the last element of RenderPassDesc::mAttachmentFormats can
    contain other information in addition to the depth/stencil format ID.
    
    The FormatID enum is rearranged such that depth/stencil formats are
    placed first, as a result occupying values in [1, 7].  These values take
    up 3 bits in an element of RenderPassDesc::mAttachmentFormats (which
    could be the last element if all color draw buffers are attached).
    
    As a result, the upper 5 bits of the last element of
    RenderPassDesc::mAttachmentFormats is unused.  It is intended for these
    bits to be used in the implementation of multisampled-render-to-texture
    depth/stencil renderbuffers.
    
    Bug: angleproject:4836
    Change-Id: I0786e0712539cdbbf5494ec83aeee1dd93f936dd
    Reviewed-on: https://chromium-review.googlesource.com/c/angle/angle/+/2413165
    Commit-Queue: Shahbaz Youssefi <syoussefi@chromium.org>
    Reviewed-by: Tim Van Patten <timvp@google.com>
    Reviewed-by: Jamie Madill <jmadill@chromium.org>
    

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    Description

    A conformant OpenGL ES implementation for Windows, Mac, Linux, iOS and Android.

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  • README.md

  • ANGLE: Vulkan Back-end

    ANGLE’s Vulkan back-end implementation lives in this folder.

    Vulkan is an explicit graphics API. It has a lot in common with other explicit APIs such as Microsoft’s D3D12 and Apple’s Metal. Compared to APIs like OpenGL or D3D11 explicit APIs can offer a number of significant benefits:

    • Lower API call CPU overhead.
    • A smaller API surface with more direct hardware control.
    • Better support for multi-core programming.
    • Vulkan in particular has open-source tooling and tests.

    Back-end Design

    The RendererVk class represents an EGLDisplay. RendererVk owns shared global resources like the VkDevice, VkQueue, the Vulkan format tables and internal Vulkan shaders. The ContextVk class implements the back-end of a front-end OpenGL Context. ContextVk processes state changes and handles action commands like glDrawArrays and glDrawElements.

    Command recording

    The back-end records commands into command buffers via the the following ContextVk APIs:

    • getOutsideRenderPassCommandBuffer: returns a secondary command buffer outside a RenderPass instance.
    • flushAndBeginRenderPass: returns a secondary command buffer inside a RenderPass instance.

    Note: All of these commands may write out (aka flush) prior pending commands into a primary command buffer. When a RenderPass is open getOutsideRenderPassCommandBuffer will flush the pending RenderPass commands. flushAndBeginRenderPass will flush out pending commands outside a RenderPass to a primary buffer. On submit ANGLE submits the primary command buffer to a VkQueue.

    If you need to record inside a RenderPass, use flushAndBeginRenderPass. Otherwise, use getOutsideRenderPassCommandBuffer.

    The back-end (mostly) records Image and Buffer barriers through additional ContextVk APIs:

    • onBufferTransferRead and onBufferComputeShaderRead accumulate VkBuffer read barriers.
    • onBufferTransferWrite and onBufferComputeShaderWrite accumulate VkBuffer write barriers.
    • onBuffferSelfCopy is a special case for VkBuffer self copies. It behaves the same as write.
    • onImageTransferRead and onImageComputerShadeRead accumulate VkImage read barriers.
    • onImageTransferWrite and onImageComputerShadeWrite accumulate VkImage write barriers.
    • onImageRenderPassRead and onImageRenderPassWrite accumulate VkImage barriers inside a started RenderPass.

    After the back-end records commands to the primary buffer we flush (e.g. on swap) or when we call ContextVk::finishToSerial.

    See the code for more details.

    Simple command recording example

    In this example we’ll be recording a buffer copy command:

        # Ensure that ANGLE sets proper read and write barriers for the Buffers.
        ANGLE_TRY(contextVk->onBufferTransferWrite(destBuffer));
        ANGLE_TRY(contextVk->onBufferTransferRead(srcBuffer));
    
        # Get a pointer to a secondary command buffer for command recording. May "flush" the RP.
        vk::CommandBuffer *commandBuffer;
        ANGLE_TRY(contextVk->getOutsideRenderPassCommandBuffer(&commandBuffer));
    
        # Record the copy command into the secondary buffer. We're done!
        commandBuffer->copyBuffer(srcBuffer->getBuffer(), destBuffer->getBuffer(), copyCount, copies);

    Additional Reading

    More implementation details can be found in the doc directory: