// Copyright (c) 2020-2024 Huawei Technologies Co. Ltd.
//
// SPDX-License-Identifier: CC-BY-4.0

include::{generated}/meta/{refprefix}VK_HUAWEI_subpass_shading.txt[]

=== Other Extension Metadata

*Last Modified Date*::
    2021-06-01
*Interactions and External Dependencies*::
  - This extension requires
    https://github.com/KhronosGroup/GLSL/blob/master/extensions/huawei/GLSL_HUAWEI_subpass_shading.txt[`GL_HUAWEI_subpass_shading`].
  - This extension requires
    {spirv}/HUAWEI/SPV_HUAWEI_subpass_shading.html[`SPV_HUAWEI_subpass_shading`].
*Contributors*::
  - Hueilong Wang

=== Description

This extension allows applications to execute a subpass shading pipeline in
a subpass of a render pass in order to save memory bandwidth for algorithms
like tile-based deferred rendering and forward plus.
A subpass shading pipeline is a pipeline with the compute pipeline ability,
allowed to read values from input attachments, and only allowed to be
dispatched inside a stand-alone subpass.
Its work dimension is defined by the render pass's render area size.
Its workgroup size (width, height) shall be a power-of-two number in width
or height, with minimum value from 8, and maximum value shall be decided
from the render pass attachments and sample counts but depends on
implementation.

The code:GlobalInvocationId.xy of a subpass shading pipeline is equal to the
code:FragCoord.xy of a graphic pipeline in the same render pass subtracted
the <<VkRect2D,pname:offset>> of the
slink:VkRenderPassBeginInfo::code:renderArea.
code:GlobalInvocationId.z is mapped to the Layer if
`<<VK_EXT_shader_viewport_index_layer>>` is supported.
The code:GlobalInvocationId.xy is equal to the index of the local workgroup
multiplied by the size of the local workgroup plus the
code:LocalInvocationId and the <<VkRect2D,pname:offset>> of the
slink:VkRenderPassBeginInfo::code:renderArea.

This extension allows a subpass's pipeline bind point to be
ename:VK_PIPELINE_BIND_POINT_SUBPASS_SHADING_HUAWEI.

include::{generated}/interfaces/VK_HUAWEI_subpass_shading.txt[]


=== Sample Code

Example of subpass shading in a GLSL shader

[source,c]
---------------------------------------------------
#extension GL_HUAWEI_subpass_shading: enable
#extension GL_KHR_shader_subgroup_arithmetic: enable

layout(constant_id = 0) const uint tileWidth = 16;
layout(constant_id = 1) const uint tileHeight = 16;
layout(local_size_x_id = 0, local_size_y_id = 1, local_size_z = 1) in;
layout (set=0, binding=0, input_attachment_index=0) uniform subpassInput depth;

void main()
{
  float d = subpassLoad(depth);
  float minD = subgroupMin(d);
  float maxD = subgroupMax(d);
}
---------------------------------------------------

Example of subpass shading dispatching in a subpass

[source,c]
---------------------------------------------------
vkCmdNextSubpass(commandBuffer, VK_SUBPASS_CONTENTS_INLINE);
vkCmdBindPipeline(commandBuffer, VK_PIPELINE_BIND_POINT_SUBPASS_SHADING_HUAWEI, subpassShadingPipeline);
vkCmdBindDescriptorSets(commandBuffer, VK_PIPELINE_BIND_POINT_SUBPASS_SHADING_HUAWEI, subpassShadingPipelineLayout,
  firstSet, descriptorSetCount, pDescriptorSets, dynamicOffsetCount, pDynamicOffsets);
vkCmdSubpassShadingHUAWEI(commandBuffer)
vkCmdEndRenderPass(commandBuffer);
---------------------------------------------------

Example of subpass shading render pass creation

[source,c]
---------------------------------------------------
VkAttachmentDescription2 attachments[] = {
  {
    VK_STRUCTURE_TYPE_ATTACHMENT_DESCRIPTION_2, NULL,
    0, VK_FORMAT_R8G8B8A8_UNORM, VK_SAMPLE_COUNT_1_BIT,
    VK_ATTACHMENT_LOAD_OP_CLEAR, VK_ATTACHMENT_STORE_OP_DONT_CARE,
    VK_ATTACHMENT_LOAD_OP_DONT_CARE, VK_ATTACHMENT_LOAD_OP_DONT_CARE,
    VK_IMAGE_LAYOUT_COLOR_ATTACHMENT_OPTIMAL, VK_IMAGE_LAYOUT_COLOR_ATTACHMENT_OPTIMAL
  },
  {
    VK_STRUCTURE_TYPE_ATTACHMENT_DESCRIPTION_2, NULL,
    0, VK_FORMAT_R8G8B8A8_UNORM, VK_SAMPLE_COUNT_1_BIT,
    VK_ATTACHMENT_LOAD_OP_CLEAR, VK_ATTACHMENT_STORE_OP_DONT_CARE,
    VK_ATTACHMENT_LOAD_OP_DONT_CARE, VK_ATTACHMENT_LOAD_OP_DONT_CARE,
    VK_IMAGE_LAYOUT_COLOR_ATTACHMENT_OPTIMAL, VK_IMAGE_LAYOUT_COLOR_ATTACHMENT_OPTIMAL
  },
  {
    VK_STRUCTURE_TYPE_ATTACHMENT_DESCRIPTION_2, NULL,
    0, VK_FORMAT_R8G8B8A8_UNORM, VK_SAMPLE_COUNT_1_BIT,
    VK_ATTACHMENT_LOAD_OP_CLEAR, VK_ATTACHMENT_STORE_OP_DONT_CARE,
    VK_ATTACHMENT_LOAD_OP_DONT_CARE, VK_ATTACHMENT_LOAD_OP_DONT_CARE,
    VK_IMAGE_LAYOUT_COLOR_ATTACHMENT_OPTIMAL, VK_IMAGE_LAYOUT_COLOR_ATTACHMENT_OPTIMAL
  },
  {
    VK_STRUCTURE_TYPE_ATTACHMENT_DESCRIPTION_2, NULL,
    0, VK_FORMAT_D24_UNORM_S8_UINT, VK_SAMPLE_COUNT_1_BIT,
    VK_ATTACHMENT_LOAD_OP_CLEAR, VK_ATTACHMENT_STORE_OP_DONT_CARE,
    VK_ATTACHMENT_LOAD_OP_CLEAR, VK_ATTACHMENT_LOAD_OP_DONT_CARE,
    VK_IMAGE_LAYOUT_DEPTH_STENCIL_ATTACHMENT_OPTIMAL, VK_IMAGE_LAYOUT_DEPTH_STENCIL_ATTACHMENT_OPTIMAL
  },
  {
    VK_STRUCTURE_TYPE_ATTACHMENT_DESCRIPTION_2, NULL,
    0, VK_FORMAT_R8G8B8A8_UNORM, VK_SAMPLE_COUNT_1_BIT,
    VK_ATTACHMENT_LOAD_OP_CLEAR, VK_ATTACHMENT_STORE_OP_STORE,
    VK_ATTACHMENT_LOAD_OP_DONT_CARE, VK_ATTACHMENT_LOAD_OP_DONT_CARE,
    VK_IMAGE_LAYOUT_COLOR_ATTACHMENT_OPTIMAL, VK_IMAGE_LAYOUT_COLOR_ATTACHMENT_OPTIMAL
  }
};

VkAttachmentReference2 gBufferAttachmentReferences[] = {
  { VK_STRUCTURE_TYPE_ATTACHMENT_REFERENCE_2, NULL, 0, VK_IMAGE_LAYOUT_COLOR_ATTACHMENT_OPTIMAL, VK_IMAGE_ASPECT_COLOR_BIT },
  { VK_STRUCTURE_TYPE_ATTACHMENT_REFERENCE_2, NULL, 1, VK_IMAGE_LAYOUT_COLOR_ATTACHMENT_OPTIMAL, VK_IMAGE_ASPECT_COLOR_BIT },
  { VK_STRUCTURE_TYPE_ATTACHMENT_REFERENCE_2, NULL, 2, VK_IMAGE_LAYOUT_COLOR_ATTACHMENT_OPTIMAL, VK_IMAGE_ASPECT_COLOR_BIT }
};
VkAttachmentReference2 gBufferDepthStencilAttachmentReferences =
  { VK_STRUCTURE_TYPE_ATTACHMENT_REFERENCE_2, NULL, 3, VK_IMAGE_LAYOUT_DEPTH_STENCIL_ATTACHMENT_OPTIMAL, VK_IMAGE_ASPECT_DEPTH_BIT|VK_IMAGE_ASPECT_STENCIL_BIT };
VkAttachmentReference2 depthInputAttachmentReferences[] = {
  { VK_STRUCTURE_TYPE_ATTACHMENT_REFERENCE_2, NULL, 3, VK_IMAGE_LAYOUT_DEPTH_STENCIL_READ_ONLY_OPTIMAL, VK_IMAGE_ASPECT_DEPTH_BIT|VK_IMAGE_ASPECT_STENCIL_BIT };
};
VkAttachmentReference2 preserveAttachmentReferences[] = {
  { VK_STRUCTURE_TYPE_ATTACHMENT_REFERENCE_2, NULL, 0, VK_IMAGE_LAYOUT_COLOR_ATTACHMENT_OPTIMAL, VK_IMAGE_ASPECT_COLOR_BIT },
  { VK_STRUCTURE_TYPE_ATTACHMENT_REFERENCE_2, NULL, 1, VK_IMAGE_LAYOUT_COLOR_ATTACHMENT_OPTIMAL, VK_IMAGE_ASPECT_COLOR_BIT },
  { VK_STRUCTURE_TYPE_ATTACHMENT_REFERENCE_2, NULL, 2, VK_IMAGE_LAYOUT_COLOR_ATTACHMENT_OPTIMAL, VK_IMAGE_ASPECT_COLOR_BIT },
  { VK_STRUCTURE_TYPE_ATTACHMENT_REFERENCE_2, NULL, 3, VK_IMAGE_LAYOUT_DEPTH_STENCIL_ATTACHMENT_OPTIMAL, VK_IMAGE_ASPECT_DEPTH_BIT|VK_IMAGE_ASPECT_STENCIL_BIT }
}; // G buffer including depth/stencil
VkAttachmentReference2 colorAttachmentReferences[] = {
  { VK_STRUCTURE_TYPE_ATTACHMENT_REFERENCE_2, NULL, 4, VK_IMAGE_LAYOUT_COLOR_ATTACHMENT_OPTIMAL, VK_IMAGE_ASPECT_COLOR_BIT }
};
VkAttachmentReference2 resolveAttachmentReference =
  { VK_STRUCTURE_TYPE_ATTACHMENT_REFERENCE_2, NULL, 4, VK_IMAGE_LAYOUT_COLOR_ATTACHMENT_OPTIMAL, VK_IMAGE_ASPECT_COLOR_BIT };

VkSubpassDescription2 subpasses[] = {
  {
    VK_STRUCTURE_TYPE_SUBPASS_DESCRIPTION_2, NULL, 0, VK_PIPELINE_BIND_POINT_GRAPHICS, 0,
    0, NULL, // input
    sizeof(gBufferAttachmentReferences)/sizeof(gBufferAttachmentReferences[0]), gBufferAttachmentReferences, // color
    NULL, &gBufferDepthStencilAttachmentReferences, // resolve & DS
    0, NULL
  },
  {
    VK_STRUCTURE_TYPE_SUBPASS_DESCRIPTION_2, NULL, 0, VK_PIPELINE_BIND_POINT_SUBPASS_SHADING_HUAWEI , 0,
    sizeof(depthInputAttachmentReferences)/sizeof(depthInputAttachmentReferences[0]), depthInputAttachmentReferences, // input
    0, NULL, // color
    NULL, NULL, // resolve & DS
    sizeof(preserveAttachmentReferences)/sizeof(preserveAttachmentReferences[0]), preserveAttachmentReferences,
  },
  {
    VK_STRUCTURE_TYPE_SUBPASS_DESCRIPTION_2, NULL, 0, VK_PIPELINE_BIND_POINT_GRAPHICS, 0,
    sizeof(gBufferAttachmentReferences)/sizeof(gBufferAttachmentReferences[0]), gBufferAttachmentReferences, // input
    sizeof(colorAttachmentReferences)/sizeof(colorAttachmentReferences[0]), colorAttachmentReferences, // color
    &resolveAttachmentReference, &gBufferDepthStencilAttachmentReferences, // resolve & DS
    0, NULL
  },
};

VkMemoryBarrier2KHR fragmentToSubpassShading = {
  VK_STRUCTURE_TYPE_MEMORY_BARRIER_2_KHR, NULL,
  VK_PIPELINE_STAGE_2_FRAGMENT_SHADER_BIT_KHR, VK_ACCESS_COLOR_ATTACHMENT_WRITE_BIT|VK_ACCESS_DEPTH_STENCIL_ATTACHMENT_WRITE_BIT,
  VK_PIPELINE_STAGE_2_SUBPASS_SHADING_BIT_HUAWEI, VK_ACCESS_INPUT_ATTACHMENT_READ_BIT
};

VkMemoryBarrier2KHR subpassShadingToFragment = {
  VK_STRUCTURE_TYPE_MEMORY_BARRIER_2_KHR, NULL,
  VK_PIPELINE_STAGE_2_SUBPASS_SHADING_BIT_HUAWEI, VK_ACCESS_SHADER_WRITE_BIT,
  VK_PIPELINE_STAGE_2_FRAGMENT_SHADER_BIT_KHR, VK_ACCESS_SHADER_READ_BIT
};

VkSubpassDependency2 dependencies[] = {
  {
    VK_STRUCTURE_TYPE_SUBPASS_DEPENDENCY_2, &fragmentToSubpassShading,
    0, 1,
    0, 0, 0, 0,
    0, 0
  },
  {
    VK_STRUCTURE_TYPE_SUBPASS_DEPENDENCY_2, &subpassShadingToFragment,
    1, 2,
    0, 0, 0, 0,
    0, 0
  },
};

VkRenderPassCreateInfo2 renderPassCreateInfo = {
  VK_STRUCTURE_TYPE_RENDER_PASS_CREATE_INFO_2, NULL, 0,
    sizeof(attachments)/sizeof(attachments[0]), attachments,
    sizeof(subpasses)/sizeof(subpasses[0]), subpasses,
    sizeof(dependencies)/sizeof(dependencies[0]), dependencies,
    0, NULL
};
VKRenderPass renderPass;
vkCreateRenderPass2(device, &renderPassCreateInfo, NULL, &renderPass);
---------------------------------------------------

Example of subpass shading pipeline creation

[source,c]
---------------------------------------------------
VkExtent2D maxWorkgroupSize;

VkSpecializationMapEntry subpassShadingConstantMapEntries[] = {
  { 0, 0 * sizeof(uint32_t), sizeof(uint32_t) },
  { 1, 1 * sizeof(uint32_t), sizeof(uint32_t) }
};

VkSpecializationInfo subpassShadingConstants = {
  2, subpassShadingConstantMapEntries,
  sizeof(VkExtent2D), &maxWorkgroupSize
};

VkSubpassShadingPipelineCreateInfoHUAWEI subpassShadingPipelineCreateInfo {
  VK_STRUCTURE_TYPE_SUBPASSS_SHADING_PIPELINE_CREATE_INFO_HUAWEI, NULL,
  renderPass, 1
};

VkPipelineShaderStageCreateInfo subpassShadingPipelineStageCreateInfo {
  VK_STRUCTURE_TYPE_PIPELINE_SHADER_STAGE_CREATE_INFO, NULL,
  0, VK_SHADER_STAGE_SUBPASS_SHADING_BIT_HUAWEI,
  shaderModule, "subpass shading example",
  &subpassShadingConstants
};

VkComputePipelineCreateInfo subpassShadingComputePipelineCreateInfo = {
  VK_STRUCTURE_TYPE_COMPUTE_PIPELINE_CREATE_INFO, NULL,
  0, &subpassShadingPipelineCreateInfo,
  pipelineLayout, basePipelineHandle, basePipelineIndex
};

VKPipeline pipeline;

vkGetDeviceSubpassShadingMaxWorkgroupSizeHUAWEI(device, renderPass, &maxWorkgroupSize);
vkCreateComputePipelines(device, pipelineCache, 1, &subpassShadingComputePipelineCreateInfo, NULL, &pipeline);

---------------------------------------------------


=== Version History

  * Revision 2, 2021-06-28 (Hueilong Wang)
    - Change vkGetSubpassShadingMaxWorkgroupSizeHUAWEI to
      vkGetDeviceSubpassShadingMaxWorkgroupSizeHUAWEI to resolve issue
      https://github.com/KhronosGroup/Vulkan-Docs/issues/1564[`pub1564`]
  * Revision 1, 2020-12-15 (Hueilong Wang)
    - Initial draft.

