[Impeller] exploit perfect hash for SamplerDescriptor. (#57036)

There are only 3 or 4 sampler's active at any given time in a flutter app. rather than store them in a hashmap, just use a vector.

Author: Jonah Williams

impeller/compiler/reflector.cc

@@ -1390,7 +1390,7 @@ std::vector<Reflector::BindPrototype> Reflector::ReflectBindPrototypes(
         .argument_name = "texture",
     });
     proto.args.push_back(BindPrototypeArgument{
-        .type_name = "const std::unique_ptr<const Sampler>&",
+        .type_name = "raw_ptr<const Sampler>",
         .argument_name = "sampler",
     });
   }

impeller/core/formats.h

@@ -412,7 +412,7 @@ struct Viewport {
 /// @brief      Describes how the texture should be sampled when the texture
 ///             is being shrunk (minified) or expanded (magnified) to fit to
 ///             the sample point.
-enum class MinMagFilter {
+enum class MinMagFilter : uint8_t {
   /// Select nearest to the sample point. Most widely supported.
   kNearest,
 
@@ -422,7 +422,7 @@ enum class MinMagFilter {
 };
 
 /// @brief      Options for selecting and filtering between mipmap levels.
-enum class MipFilter {
+enum class MipFilter : uint8_t {
   /// @brief    The texture is sampled as if it only had a single mipmap level.
   ///
   ///           All samples are read from level 0.
@@ -438,7 +438,7 @@ enum class MipFilter {
   kLinear,
 };
 
-enum class SamplerAddressMode {
+enum class SamplerAddressMode : uint8_t {
   kClampToEdge,
   kRepeat,
   kMirror,

impeller/core/resource_binder.h

@@ -9,6 +9,7 @@
 
 #include "impeller/core/buffer_view.h"
 #include "impeller/core/formats.h"
+#include "impeller/core/raw_ptr.h"
 #include "impeller/core/sampler.h"
 #include "impeller/core/shader_types.h"
 #include "impeller/core/texture.h"
@@ -34,7 +35,7 @@ struct ResourceBinder {
                             const SampledImageSlot& slot,
                             const ShaderMetadata* metadata,
                             std::shared_ptr<const Texture> texture,
-                            const std::unique_ptr<const Sampler>& sampler) = 0;
+                            raw_ptr<const Sampler>) = 0;
 };
 
 }  // namespace impeller

impeller/core/sampler.cc

@@ -6,7 +6,7 @@
 
 namespace impeller {
 
-Sampler::Sampler(SamplerDescriptor desc) : desc_(std::move(desc)) {}
+Sampler::Sampler(const SamplerDescriptor& desc) : desc_(desc) {}
 
 Sampler::~Sampler() = default;
 

impeller/core/sampler.h

@@ -5,9 +5,6 @@
 #ifndef FLUTTER_IMPELLER_CORE_SAMPLER_H_
 #define FLUTTER_IMPELLER_CORE_SAMPLER_H_
 
-#include <unordered_map>
-
-#include "impeller/base/comparable.h"
 #include "impeller/core/sampler_descriptor.h"
 
 namespace impeller {
@@ -21,19 +18,14 @@ class Sampler {
  protected:
   SamplerDescriptor desc_;
 
-  explicit Sampler(SamplerDescriptor desc);
+  explicit Sampler(const SamplerDescriptor& desc);
 
  private:
   Sampler(const Sampler&) = delete;
 
   Sampler& operator=(const Sampler&) = delete;
 };
 
-using SamplerMap = std::unordered_map<SamplerDescriptor,
-                                      std::unique_ptr<const Sampler>,
-                                      ComparableHash<SamplerDescriptor>,
-                                      ComparableEqual<SamplerDescriptor>>;
-
 }  // namespace impeller
 
 #endif  // FLUTTER_IMPELLER_CORE_SAMPLER_H_

impeller/core/sampler_descriptor.h

@@ -5,14 +5,13 @@
 #ifndef FLUTTER_IMPELLER_CORE_SAMPLER_DESCRIPTOR_H_
 #define FLUTTER_IMPELLER_CORE_SAMPLER_DESCRIPTOR_H_
 
-#include "impeller/base/comparable.h"
 #include "impeller/core/formats.h"
 
 namespace impeller {
 
 class Context;
 
-struct SamplerDescriptor final : public Comparable<SamplerDescriptor> {
+struct SamplerDescriptor final {
   MinMagFilter min_filter = MinMagFilter::kNearest;
   MinMagFilter mag_filter = MinMagFilter::kNearest;
   MipFilter mip_filter = MipFilter::kNearest;
@@ -30,20 +29,17 @@ struct SamplerDescriptor final : public Comparable<SamplerDescriptor> {
                     MinMagFilter mag_filter,
                     MipFilter mip_filter);
 
-  // Comparable<SamplerDescriptor>
-  std::size_t GetHash() const override {
-    return fml::HashCombine(min_filter, mag_filter, mip_filter,
-                            width_address_mode, height_address_mode,
-                            depth_address_mode);
-  }
-
-  // Comparable<SamplerDescriptor>
-  bool IsEqual(const SamplerDescriptor& o) const override {
-    return min_filter == o.min_filter && mag_filter == o.mag_filter &&
-           mip_filter == o.mip_filter &&
-           width_address_mode == o.width_address_mode &&
-           height_address_mode == o.height_address_mode &&
-           depth_address_mode == o.depth_address_mode;
+  static uint64_t ToKey(const SamplerDescriptor& d) {
+    static_assert(sizeof(MinMagFilter) == 1);
+    static_assert(sizeof(MipFilter) == 1);
+    static_assert(sizeof(SamplerAddressMode) == 1);
+
+    return static_cast<uint64_t>(d.min_filter) << 0 |
+           static_cast<uint64_t>(d.mag_filter) << 8 |
+           static_cast<uint64_t>(d.mip_filter) << 16 |
+           static_cast<uint64_t>(d.width_address_mode) << 24 |
+           static_cast<uint64_t>(d.height_address_mode) << 32 |
+           static_cast<uint64_t>(d.depth_address_mode) << 40;
   }
 };
 

impeller/display_list/canvas.cc

@@ -658,22 +658,22 @@ void Canvas::DrawPoints(const Point points[],
 void Canvas::DrawImage(const std::shared_ptr<Texture>& image,
                        Point offset,
                        const Paint& paint,
-                       SamplerDescriptor sampler) {
+                       const SamplerDescriptor& sampler) {
   if (!image) {
     return;
   }
 
   const auto source = Rect::MakeSize(image->GetSize());
   const auto dest = source.Shift(offset);
 
-  DrawImageRect(image, source, dest, paint, std::move(sampler));
+  DrawImageRect(image, source, dest, paint, sampler);
 }
 
 void Canvas::DrawImageRect(const std::shared_ptr<Texture>& image,
                            Rect source,
                            Rect dest,
                            const Paint& paint,
-                           SamplerDescriptor sampler,
+                           const SamplerDescriptor& sampler,
                            SourceRectConstraint src_rect_constraint) {
   if (!image || source.IsEmpty() || dest.IsEmpty()) {
     return;
@@ -704,7 +704,7 @@ void Canvas::DrawImageRect(const std::shared_ptr<Texture>& image,
   texture_contents->SetSourceRect(*clipped_source);
   texture_contents->SetStrictSourceRect(src_rect_constraint ==
                                         SourceRectConstraint::kStrict);
-  texture_contents->SetSamplerDescriptor(std::move(sampler));
+  texture_contents->SetSamplerDescriptor(sampler);
   texture_contents->SetOpacity(paint.color.alpha);
   texture_contents->SetDeferApplyingOpacity(paint.HasColorFilter());
 

impeller/display_list/canvas.h

@@ -209,14 +209,14 @@ class Canvas {
   void DrawImage(const std::shared_ptr<Texture>& image,
                  Point offset,
                  const Paint& paint,
-                 SamplerDescriptor sampler = {});
+                 const SamplerDescriptor& sampler = {});
 
   void DrawImageRect(
       const std::shared_ptr<Texture>& image,
       Rect source,
       Rect dest,
       const Paint& paint,
-      SamplerDescriptor sampler = {},
+      const SamplerDescriptor& sampler = {},
       SourceRectConstraint src_rect_constraint = SourceRectConstraint::kFast);
 
   void DrawTextFrame(const std::shared_ptr<TextFrame>& text_frame,

impeller/entity/contents/atlas_contents.cc

@@ -47,7 +47,7 @@ bool AtlasContents::Render(const ContentContext& renderer,
     dst_sampler_descriptor.width_address_mode = SamplerAddressMode::kDecal;
     dst_sampler_descriptor.height_address_mode = SamplerAddressMode::kDecal;
   }
-  const std::unique_ptr<const Sampler>& dst_sampler =
+  raw_ptr<const Sampler> dst_sampler =
       renderer.GetContext()->GetSamplerLibrary()->GetSampler(
           dst_sampler_descriptor);
 
@@ -58,7 +58,7 @@ bool AtlasContents::Render(const ContentContext& renderer,
 
     auto dst_sampler_descriptor = geometry_->GetSamplerDescriptor();
 
-    const std::unique_ptr<const Sampler>& dst_sampler =
+    raw_ptr<const Sampler> dst_sampler =
         renderer.GetContext()->GetSamplerLibrary()->GetSampler(
             dst_sampler_descriptor);
 

impeller/entity/contents/filters/blend_filter_contents.cc

@@ -204,7 +204,7 @@ static std::optional<Entity> AdvancedBlend(
       dst_sampler_descriptor.width_address_mode = SamplerAddressMode::kDecal;
       dst_sampler_descriptor.height_address_mode = SamplerAddressMode::kDecal;
     }
-    const std::unique_ptr<const Sampler>& dst_sampler =
+    raw_ptr<const Sampler> dst_sampler =
         renderer.GetContext()->GetSamplerLibrary()->GetSampler(
             dst_sampler_descriptor);
     FS::BindTextureSamplerDst(pass, dst_snapshot->texture, dst_sampler);
@@ -227,7 +227,7 @@ static std::optional<Entity> AdvancedBlend(
         src_sampler_descriptor.width_address_mode = SamplerAddressMode::kDecal;
         src_sampler_descriptor.height_address_mode = SamplerAddressMode::kDecal;
       }
-      const std::unique_ptr<const Sampler>& src_sampler =
+      raw_ptr<const Sampler> src_sampler =
           renderer.GetContext()->GetSamplerLibrary()->GetSampler(
               src_sampler_descriptor);
       blend_info.color_factor = 0;
@@ -377,7 +377,7 @@ std::optional<Entity> BlendFilterContents::CreateForegroundAdvancedBlend(
       dst_sampler_descriptor.width_address_mode = SamplerAddressMode::kDecal;
       dst_sampler_descriptor.height_address_mode = SamplerAddressMode::kDecal;
     }
-    const std::unique_ptr<const Sampler>& dst_sampler =
+    raw_ptr<const Sampler> dst_sampler =
         renderer.GetContext()->GetSamplerLibrary()->GetSampler(
             dst_sampler_descriptor);
     FS::BindTextureSamplerDst(pass, dst_snapshot->texture, dst_sampler);
@@ -484,7 +484,7 @@ std::optional<Entity> BlendFilterContents::CreateForegroundPorterDuffBlend(
       dst_sampler_descriptor.width_address_mode = SamplerAddressMode::kDecal;
       dst_sampler_descriptor.height_address_mode = SamplerAddressMode::kDecal;
     }
-    const std::unique_ptr<const Sampler>& dst_sampler =
+    raw_ptr<const Sampler> dst_sampler =
         renderer.GetContext()->GetSamplerLibrary()->GetSampler(
             dst_sampler_descriptor);
     FS::BindTextureSamplerDst(pass, dst_snapshot->texture, dst_sampler);
@@ -577,7 +577,7 @@ static std::optional<Entity> PipelineBlend(
         return false;
       }
 
-      const std::unique_ptr<const Sampler>& sampler =
+      raw_ptr<const Sampler> sampler =
           renderer.GetContext()->GetSamplerLibrary()->GetSampler(
               input->sampler_descriptor);
       FS::BindTextureSampler(pass, input->texture, sampler);
@@ -853,7 +853,7 @@ std::optional<Entity> BlendFilterContents::CreateFramebufferAdvancedBlend(
         src_sampler_descriptor.width_address_mode = SamplerAddressMode::kDecal;
         src_sampler_descriptor.height_address_mode = SamplerAddressMode::kDecal;
       }
-      const std::unique_ptr<const Sampler>& src_sampler =
+      raw_ptr<const Sampler> src_sampler =
           renderer.GetContext()->GetSamplerLibrary()->GetSampler(
               src_sampler_descriptor);
       FS::BindTextureSamplerSrc(pass, src_texture, src_sampler);