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    • By mellinoe
      Hi all,
      First time poster here, although I've been reading posts here for quite a while. This place has been invaluable for learning graphics programming -- thanks for a great resource!
      Right now, I'm working on a graphics abstraction layer for .NET which supports D3D11, Vulkan, and OpenGL at the moment. I have implemented most of my planned features already, and things are working well. Some remaining features that I am planning are Compute Shaders, and some flavor of read-write shader resources. At the moment, my shaders can just get simple read-only access to a uniform (or constant) buffer, a texture, or a sampler. Unfortunately, I'm having a tough time grasping the distinctions between all of the different kinds of read-write resources that are available. In D3D alone, there seem to be 5 or 6 different kinds of resources with similar but different characteristics. On top of that, I get the impression that some of them are more or less "obsoleted" by the newer kinds, and don't have much of a place in modern code. There seem to be a few pivots:
      The data source/destination (buffer or texture) Read-write or read-only Structured or unstructured (?) Ordered vs unordered (?) These are just my observations based on a lot of MSDN and OpenGL doc reading. For my library, I'm not interested in exposing every possibility to the user -- just trying to find a good "middle-ground" that can be represented cleanly across API's which is good enough for common scenarios.
      Can anyone give a sort of "overview" of the different options, and perhaps compare/contrast the concepts between Direct3D, OpenGL, and Vulkan? I'd also be very interested in hearing how other folks have abstracted these concepts in their libraries.
    • By GuyWithBeard
      Hi,
      In Vulkan you have render passes where you specify which attachments to render to and which to read from, and subpasses within the render pass which can depend on each other. If one subpass needs to finish before another can begin you specify that with a subpass dependency.
      In my engine I don't currently use subpasses as the concept of the "render pass" translates roughly to setting a render target and clearing it followed by a number of draw calls in DirectX, while there isn't really any good way to model subpasses in DX. Because of this, in Vulkan, my frame mostly consists of a number of render passes each with one subpass.
      My question is, do I have to specify dependencies between the render passes or is that needed only if you have multiple subpasses?
      In the Vulkan Programming Guide, chapter 13 it says: "In the example renderpass we set up in Chapter 7, we used a single subpass with no dependencies and a single set of outputs.”, which suggests that you only need dependencies between subpasses, not between render passes. However, the (excellent) tutorials at vulkan-tutorial.com have you creating a subpass dependency to "external subpasses" in the chapter on "Rendering and presentation", under "Subpass dependencies": https://vulkan-tutorial.com/Drawing_a_triangle/Drawing/Rendering_and_presentation even if they are using only one render pass with a single subpass.
      So, in short; If I have render pass A, with a single subpass, rendering to an attachment and render pass B, also with a single subpass, rendering to that same attachment, do I have to specify subpass dependencies between the two subpasses of the render passes, in order to make render pass A finish before B can begin, or are they handled implicitly by the fact that they belong to different render passes?
      Thanks!
    • By mark_braga
      I am looking at the SaschaWillems subpass example for getting some insight into subpass depdendencies but its hard to understand whats going on without any comments. Also there is not a lot of documentation on subpass dependencies overall.
      Looking at the code, I can see that user specifies the src subpass, dst subpass and src state, dst state. But there is no mention of which resource the dependency is on. Is a subpass dependency like a pipeline barrier. If yes, how does it issue the barrier? Is the pipeline barrier issued on all attachments in the subpass with the input src and dst access flags? Any explanation will really clear a lot of doubts on subpass dependencies.
      Thank you
    • By mark_braga
      I need to index into a texture array using indices which are not dynamically uniform. This works fine on NVIDIA chips but you can see the artifacts on AMD due to the wavefront problem. This means, a lot of pixel invocations get the wrong index value. I know you fix this by using NonUniformResourceIndex in hlsl. Is there an equivalent for Vulkan glsl?
      This is the shader code for reference. As you can see, index is an arbitrary value for each pixel and is not dynamically uniform. I fix this for hlsl by using NonUniformResourceIndex(index)
      layout(set = 0, binding = 0) uniform sampler textureSampler; layout(set = 0, binding = 1) uniform texture2D albedoMaps[256]; layout(location = 0) out vec4 oColor; void main() { uint index = calculate_arbitrary_texture_index(); vec2 texCoord = calculate_texcoord(); vec4 albedo = texture(sampler2D(albedoMaps[index], textureSampler), texCoord); oColor = albedo; } Thank you
    • By Mercesa
      As the title says, I am explicitly creating a too small descriptor pool, which should NOT support the resources I am going to allocate from it.
       
      std::array<vk::DescriptorPoolSize, 3> type_count; // Initialize our pool with these values type_count[0].type = vk::DescriptorType::eCombinedImageSampler; type_count[0].descriptorCount = 0; type_count[1].type = vk::DescriptorType::eSampler; type_count[1].descriptorCount = 0; type_count[2].type = vk::DescriptorType::eUniformBuffer; type_count[2].descriptorCount = 0; vk::DescriptorPoolCreateInfo createInfo = vk::DescriptorPoolCreateInfo() .setPNext(nullptr) .setMaxSets(iMaxSets) .setPoolSizeCount(type_count.size()) .setPPoolSizes(type_count.data()); pool = aDevice.createDescriptorPool(createInfo);  
      I have an allocation function which looks like this, I am allocating a uniform, image-combined sampler and a regular sampler. Though if my pool is empty this should not work?
      vk::DescriptorSetAllocateInfo alloc_info[1] = {}; alloc_info[0].pNext = NULL; alloc_info[0].setDescriptorPool(pool); alloc_info[0].setDescriptorSetCount(iNumToAllocate); alloc_info[0].setPSetLayouts(&iDescriptorLayouts); std::vector<vk::DescriptorSet> tDescriptors; tDescriptors.resize(iNumToAllocate); iDevice.allocateDescriptorSets(alloc_info, tDescriptors.data());  
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