[Impeller] remove std::vector usage in render pass vk. (#57132)

Remove std::vector usage in vulkan render pass. Fixed size array + offsets, should be faster than heap allocations.

Author: Jonah Williams

impeller/renderer/backend/vulkan/render_pass_builder_vk.cc

@@ -4,8 +4,6 @@
 
 #include "impeller/renderer/backend/vulkan/render_pass_builder_vk.h"
 
-#include <vector>
-
 #include "impeller/core/formats.h"
 #include "impeller/renderer/backend/vulkan/formats_vk.h"
 #include "vulkan/vulkan_enums.hpp"
@@ -119,57 +117,64 @@ vk::UniqueRenderPass RenderPassBuilderVK::Build(
     color_attachments_count++;
   }
 
-  std::vector<vk::AttachmentDescription> attachments;
-
-  std::vector<vk::AttachmentReference> color_refs(color_attachments_count,
-                                                  kUnusedAttachmentReference);
-  std::vector<vk::AttachmentReference> resolve_refs(color_attachments_count,
-                                                    kUnusedAttachmentReference);
+  std::array<vk::AttachmentDescription, kMaxAttachments> attachments;
+  std::array<vk::AttachmentReference, kMaxColorAttachments> color_refs;
+  std::array<vk::AttachmentReference, kMaxColorAttachments> resolve_refs;
   vk::AttachmentReference depth_stencil_ref = kUnusedAttachmentReference;
+  size_t attachments_index = 0;
+  size_t color_index = 0;
+  size_t resolve_index = 0;
 
   if (color0_.has_value()) {
     vk::AttachmentReference color_ref;
-    color_ref.attachment = attachments.size();
+    color_ref.attachment = attachments_index;
     color_ref.layout = vk::ImageLayout::eGeneral;
-    color_refs[0] = color_ref;
-    attachments.push_back(color0_.value());
+    color_refs.at(color_index++) = color_ref;
+    attachments.at(attachments_index++) = color0_.value();
 
     if (color0_resolve_.has_value()) {
       vk::AttachmentReference resolve_ref;
-      resolve_ref.attachment = attachments.size();
+      resolve_ref.attachment = attachments_index;
       resolve_ref.layout = vk::ImageLayout::eGeneral;
-      resolve_refs[0] = resolve_ref;
-      attachments.push_back(color0_resolve_.value());
+      resolve_refs.at(resolve_index++) = resolve_ref;
+      attachments.at(attachments_index++) = color0_resolve_.value();
+    } else {
+      resolve_refs.at(resolve_index++) = kUnusedAttachmentReference;
     }
   }
 
   for (const auto& color : colors_) {
     vk::AttachmentReference color_ref;
-    color_ref.attachment = attachments.size();
+    color_ref.attachment = attachments_index;
     color_ref.layout = vk::ImageLayout::eGeneral;
-    color_refs[color.first] = color_ref;
-    attachments.push_back(color.second);
+    color_refs.at(color_index++) = color_ref;
+    attachments.at(attachments_index++) = color.second;
 
     if (auto found = resolves_.find(color.first); found != resolves_.end()) {
       vk::AttachmentReference resolve_ref;
-      resolve_ref.attachment = attachments.size();
+      resolve_ref.attachment = attachments_index;
       resolve_ref.layout = vk::ImageLayout::eGeneral;
-      resolve_refs[color.first] = resolve_ref;
-      attachments.push_back(found->second);
+      resolve_refs.at(resolve_index++) = resolve_ref;
+      attachments.at(attachments_index++) = found->second;
+    } else {
+      resolve_refs.at(resolve_index++) = kUnusedAttachmentReference;
     }
   }
 
   if (depth_stencil_.has_value()) {
-    depth_stencil_ref.attachment = attachments.size();
+    depth_stencil_ref.attachment = attachments_index;
     depth_stencil_ref.layout = vk::ImageLayout::eGeneral;
-    attachments.push_back(depth_stencil_.value());
+    attachments.at(attachments_index++) = depth_stencil_.value();
   }
 
   vk::SubpassDescription subpass0;
   subpass0.pipelineBindPoint = vk::PipelineBindPoint::eGraphics;
-  subpass0.setInputAttachments(color_refs);
-  subpass0.setColorAttachments(color_refs);
-  subpass0.setResolveAttachments(resolve_refs);
+  subpass0.setPInputAttachments(color_refs.data());
+  subpass0.setInputAttachmentCount(color_index);
+  subpass0.setPColorAttachments(color_refs.data());
+  subpass0.setColorAttachmentCount(color_index);
+  subpass0.setPResolveAttachments(resolve_refs.data());
+
   subpass0.setPDepthStencilAttachment(&depth_stencil_ref);
 
   vk::SubpassDependency self_dep;
@@ -182,7 +187,8 @@ vk::UniqueRenderPass RenderPassBuilderVK::Build(
   self_dep.dependencyFlags = kSelfDependencyFlags;
 
   vk::RenderPassCreateInfo render_pass_desc;
-  render_pass_desc.setAttachments(attachments);
+  render_pass_desc.setPAttachments(attachments.data());
+  render_pass_desc.setAttachmentCount(attachments_index);
   render_pass_desc.setSubpasses(subpass0);
   render_pass_desc.setDependencies(self_dep);
 

impeller/renderer/backend/vulkan/render_pass_builder_vk.h

@@ -8,13 +8,16 @@
 #include <map>
 #include <optional>
 
-#include "flutter/fml/macros.h"
 #include "impeller/core/formats.h"
 #include "impeller/renderer/backend/vulkan/context_vk.h"
 #include "impeller/renderer/backend/vulkan/vk.h"
 
 namespace impeller {
 
+static constexpr size_t kMaxColorAttachments = 16;
+static constexpr size_t kMaxAttachments =
+    (kMaxColorAttachments * 2) + 1;  // MSAA + resolve plus depth/stencil
+
 class RenderPassBuilderVK {
  public:
   RenderPassBuilderVK();

impeller/renderer/backend/vulkan/render_pass_vk.cc

@@ -6,7 +6,6 @@
 
 #include <array>
 #include <cstdint>
-#include <vector>
 
 #include "fml/status.h"
 #include "impeller/base/validation.h"
@@ -52,15 +51,16 @@ static vk::ClearDepthStencilValue VKClearValueFromDepthStencil(uint32_t stencil,
   return value;
 }
 
-static std::vector<vk::ClearValue> GetVKClearValues(
-    const RenderTarget& target) {
-  std::vector<vk::ClearValue> clears;
-
+static size_t GetVKClearValues(
+    const RenderTarget& target,
+    std::array<vk::ClearValue, kMaxAttachments>& values) {
+  size_t offset = 0u;
   target.IterateAllColorAttachments(
-      [&clears](size_t index, const ColorAttachment& attachment) -> bool {
-        clears.emplace_back(VKClearValueFromColor(attachment.clear_color));
+      [&values, &offset](size_t index,
+                         const ColorAttachment& attachment) -> bool {
+        values.at(offset++) = VKClearValueFromColor(attachment.clear_color);
         if (attachment.resolve_texture) {
-          clears.emplace_back(VKClearValueFromColor(attachment.clear_color));
+          values.at(offset++) = VKClearValueFromColor(attachment.clear_color);
         }
         return true;
       });
@@ -69,14 +69,13 @@ static std::vector<vk::ClearValue> GetVKClearValues(
   const auto& stencil = target.GetStencilAttachment();
 
   if (depth.has_value()) {
-    clears.emplace_back(VKClearValueFromDepthStencil(
-        stencil ? stencil->clear_stencil : 0u, depth->clear_depth));
+    values.at(offset++) = VKClearValueFromDepthStencil(
+        stencil ? stencil->clear_stencil : 0u, depth->clear_depth);
   } else if (stencil.has_value()) {
-    clears.emplace_back(VKClearValueFromDepthStencil(
-        stencil->clear_stencil, depth ? depth->clear_depth : 0.0f));
+    values.at(offset++) = VKClearValueFromDepthStencil(
+        stencil->clear_stencil, depth ? depth->clear_depth : 0.0f);
   }
-
-  return clears;
+  return offset;
 }
 
 SharedHandleVK<vk::RenderPass> RenderPassVK::CreateVKRenderPass(
@@ -191,15 +190,17 @@ RenderPassVK::RenderPassVK(const std::shared_ptr<const Context>& context,
     TextureVK::Cast(*resolve_image_vk_).SetCachedRenderPass(render_pass_);
   }
 
-  auto clear_values = GetVKClearValues(render_target_);
+  std::array<vk::ClearValue, kMaxAttachments> clears;
+  size_t clear_count = GetVKClearValues(render_target_, clears);
 
   vk::RenderPassBeginInfo pass_info;
   pass_info.renderPass = *render_pass_;
   pass_info.framebuffer = *framebuffer;
   pass_info.renderArea.extent.width = static_cast<uint32_t>(target_size.width);
   pass_info.renderArea.extent.height =
       static_cast<uint32_t>(target_size.height);
-  pass_info.setClearValues(clear_values);
+  pass_info.setPClearValues(clears.data());
+  pass_info.setClearValueCount(clear_count);
 
   command_buffer_vk_.beginRenderPass(pass_info, vk::SubpassContents::eInline);
 
@@ -252,34 +253,37 @@ SharedHandleVK<vk::Framebuffer> RenderPassVK::CreateVKFramebuffer(
   fb_info.height = target_size.height;
   fb_info.layers = 1u;
 
-  std::vector<vk::ImageView> attachments;
+  std::array<vk::ImageView, kMaxAttachments> attachments;
+  size_t count = 0;
 
   // This bit must be consistent to ensure compatibility with the pass created
   // earlier. Follow this order: Color attachments, then depth-stencil, then
   // stencil.
   render_target_.IterateAllColorAttachments(
-      [&attachments](size_t index, const ColorAttachment& attachment) -> bool {
+      [&attachments, &count](size_t index,
+                             const ColorAttachment& attachment) -> bool {
         // The bind point doesn't matter here since that information is present
         // in the render pass.
-        attachments.emplace_back(
-            TextureVK::Cast(*attachment.texture).GetRenderTargetView());
+        attachments[count++] =
+            TextureVK::Cast(*attachment.texture).GetRenderTargetView();
         if (attachment.resolve_texture) {
-          attachments.emplace_back(TextureVK::Cast(*attachment.resolve_texture)
-                                       .GetRenderTargetView());
+          attachments[count++] = TextureVK::Cast(*attachment.resolve_texture)
+                                     .GetRenderTargetView();
         }
         return true;
       });
 
   if (auto depth = render_target_.GetDepthAttachment(); depth.has_value()) {
-    attachments.emplace_back(
-        TextureVK::Cast(*depth->texture).GetRenderTargetView());
+    attachments[count++] =
+        TextureVK::Cast(*depth->texture).GetRenderTargetView();
   } else if (auto stencil = render_target_.GetStencilAttachment();
              stencil.has_value()) {
-    attachments.emplace_back(
-        TextureVK::Cast(*stencil->texture).GetRenderTargetView());
+    attachments[count++] =
+        TextureVK::Cast(*stencil->texture).GetRenderTargetView();
   }
 
-  fb_info.setAttachments(attachments);
+  fb_info.setPAttachments(attachments.data());
+  fb_info.setAttachmentCount(count);
 
   auto [result, framebuffer] =
       context.GetDevice().createFramebufferUnique(fb_info);