[Impeller] Use a device buffer for SkBitmap allocation, use Linear texture on Metal backend. (flutter#41374)

This reduces the cost of uploading the glyph atlas, as we can exploit metal's capabilies to create a texture from a device buffer and share the underlying memory with a linear texture. This also means that subsequent updates don't require uploads or copies either.

From scrolling through wonderous, this shaves off about 0.2 ms (0.6 ms -> 0.4 ms) of fresh atlas construction.

Author: Jonah Williams

impeller/renderer/backend/metal/context_mtl.mm

@@ -55,6 +55,7 @@ static bool DeviceSupportsComputeSubgroups(id<MTLDevice> device) {
       .SetSupportsBufferToTextureBlits(true)
       .SetSupportsTextureToTextureBlits(true)
       .SetSupportsDecalTileMode(true)
+      .SetSupportsSharedDeviceBufferTextureMemory(true)
       .SetSupportsFramebufferFetch(DeviceSupportsFramebufferFetch(device))
       .SetDefaultColorFormat(color_format)
       .SetDefaultStencilFormat(PixelFormat::kS8UInt)

impeller/renderer/backend/vulkan/capabilities_vk.cc

@@ -348,10 +348,16 @@ bool CapabilitiesVK::SupportsReadFromOnscreenTexture() const {
   return false;
 }
 
+// |Capabilities|
 bool CapabilitiesVK::SupportsDecalTileMode() const {
   return true;
 }
 
+// |Capabilities|
+bool CapabilitiesVK::SupportsSharedDeviceBufferTextureMemory() const {
+  return false;
+}
+
 // |Capabilities|
 PixelFormat CapabilitiesVK::GetDefaultColorFormat() const {
   return color_format_;

impeller/renderer/backend/vulkan/capabilities_vk.h

@@ -79,6 +79,9 @@ class CapabilitiesVK final : public Capabilities,
   // |Capabilities|
   bool SupportsDecalTileMode() const override;
 
+  // |Capabilities|
+  bool SupportsSharedDeviceBufferTextureMemory() const override;
+
   // |Capabilities|
   PixelFormat GetDefaultColorFormat() const override;
 

impeller/renderer/capabilities.cc

@@ -66,6 +66,11 @@ class StandardCapabilities final : public Capabilities {
     return supports_decal_tile_mode_;
   }
 
+  // |Capabilities|
+  bool SupportsSharedDeviceBufferTextureMemory() const override {
+    return supports_shared_device_buffer_texture_memory_;
+  }
+
   // |Capabilities|
   PixelFormat GetDefaultColorFormat() const override {
     return default_color_format_;
@@ -88,6 +93,7 @@ class StandardCapabilities final : public Capabilities {
                        bool supports_read_from_onscreen_texture,
                        bool supports_read_from_resolve,
                        bool supports_decal_tile_mode,
+                       bool supports_shared_device_buffer_texture_memory,
                        PixelFormat default_color_format,
                        PixelFormat default_stencil_format)
       : has_threading_restrictions_(has_threading_restrictions),
@@ -102,6 +108,8 @@ class StandardCapabilities final : public Capabilities {
             supports_read_from_onscreen_texture),
         supports_read_from_resolve_(supports_read_from_resolve),
         supports_decal_tile_mode_(supports_decal_tile_mode),
+        supports_shared_device_buffer_texture_memory_(
+            supports_shared_device_buffer_texture_memory),
         default_color_format_(default_color_format),
         default_stencil_format_(default_stencil_format) {}
 
@@ -118,6 +126,7 @@ class StandardCapabilities final : public Capabilities {
   bool supports_read_from_onscreen_texture_ = false;
   bool supports_read_from_resolve_ = false;
   bool supports_decal_tile_mode_ = false;
+  bool supports_shared_device_buffer_texture_memory_ = false;
   PixelFormat default_color_format_ = PixelFormat::kUnknown;
   PixelFormat default_stencil_format_ = PixelFormat::kUnknown;
 
@@ -202,6 +211,12 @@ CapabilitiesBuilder& CapabilitiesBuilder::SetSupportsDecalTileMode(bool value) {
   return *this;
 }
 
+CapabilitiesBuilder&
+CapabilitiesBuilder::SetSupportsSharedDeviceBufferTextureMemory(bool value) {
+  supports_shared_device_buffer_texture_memory_ = value;
+  return *this;
+}
+
 std::unique_ptr<Capabilities> CapabilitiesBuilder::Build() {
   return std::unique_ptr<StandardCapabilities>(new StandardCapabilities(  //
       has_threading_restrictions_,                                        //
@@ -215,6 +230,7 @@ std::unique_ptr<Capabilities> CapabilitiesBuilder::Build() {
       supports_read_from_onscreen_texture_,                               //
       supports_read_from_resolve_,                                        //
       supports_decal_tile_mode_,                                          //
+      supports_shared_device_buffer_texture_memory_,                      //
       *default_color_format_,                                             //
       *default_stencil_format_                                            //
       ));

impeller/renderer/capabilities.h

@@ -37,6 +37,8 @@ class Capabilities {
 
   virtual bool SupportsDecalTileMode() const = 0;
 
+  virtual bool SupportsSharedDeviceBufferTextureMemory() const = 0;
+
   virtual PixelFormat GetDefaultColorFormat() const = 0;
 
   virtual PixelFormat GetDefaultStencilFormat() const = 0;
@@ -79,6 +81,8 @@ class CapabilitiesBuilder {
 
   CapabilitiesBuilder& SetSupportsDecalTileMode(bool value);
 
+  CapabilitiesBuilder& SetSupportsSharedDeviceBufferTextureMemory(bool value);
+
   std::unique_ptr<Capabilities> Build();
 
  private:
@@ -93,6 +97,7 @@ class CapabilitiesBuilder {
   bool supports_read_from_onscreen_texture_ = false;
   bool supports_read_from_resolve_ = false;
   bool supports_decal_tile_mode_ = false;
+  bool supports_shared_device_buffer_texture_memory_ = false;
   std::optional<PixelFormat> default_color_format_ = std::nullopt;
   std::optional<PixelFormat> default_stencil_format_ = std::nullopt;
 

impeller/renderer/capabilities_unittests.cc

@@ -29,6 +29,7 @@ CAPABILITY_TEST(SupportsComputeSubgroups, false);
 CAPABILITY_TEST(SupportsReadFromOnscreenTexture, false);
 CAPABILITY_TEST(SupportsReadFromResolve, false);
 CAPABILITY_TEST(SupportsDecalTileMode, false);
+CAPABILITY_TEST(SupportsSharedDeviceBufferTextureMemory, false);
 
 }  // namespace testing
 }  // namespace impeller