Add capability check.

impeller/entity/shaders/glyph_atlas.frag

@@ -16,5 +16,5 @@ out f16vec4 frag_color;
 
 void main() {
   f16vec4 value = texture(glyph_atlas_sampler, v_uv);
-  frag_color = max(value.rrrr, value.aaaa) * v_text_color;
+  frag_color = vec4(max(value.r, value.a)) * v_text_color;
 }

impeller/renderer/backend/gles/capabilities_gles.cc

@@ -4,6 +4,7 @@
 
 #include "impeller/renderer/backend/gles/capabilities_gles.h"
 
+#include "impeller/core/formats.h"
 #include "impeller/renderer/backend/gles/proc_table_gles.h"
 
 namespace impeller {
@@ -102,6 +103,12 @@ CapabilitiesGLES::CapabilitiesGLES(const ProcTableGLES& gl) {
     num_shader_binary_formats = value;
   }
 
+  if (desc->IsES()) {
+    default_glyph_atlas_format_ = PixelFormat::kA8UNormInt;
+  } else {
+    default_glyph_atlas_format_ = PixelFormat::kR8UNormInt;
+  }
+
   supports_framebuffer_fetch_ = desc->HasExtension(kFramebufferFetchExt);
 
   if (desc->HasExtension(kTextureBorderClampExt) ||
@@ -188,4 +195,8 @@ PixelFormat CapabilitiesGLES::GetDefaultDepthStencilFormat() const {
   return PixelFormat::kD24UnormS8Uint;
 }
 
+PixelFormat CapabilitiesGLES::GetDefaultGlyphAtlasFormat() const {
+  return default_glyph_atlas_format_;
+}
+
 }  // namespace impeller

impeller/renderer/backend/gles/capabilities_gles.h

@@ -8,6 +8,7 @@
 #include <cstddef>
 
 #include "impeller/base/backend_cast.h"
+#include "impeller/core/formats.h"
 #include "impeller/core/shader_types.h"
 #include "impeller/geometry/size.h"
 #include "impeller/renderer/capabilities.h"
@@ -116,11 +117,16 @@ class CapabilitiesGLES final
   // |Capabilities|
   PixelFormat GetDefaultDepthStencilFormat() const override;
 
+  // |Capabilities|
+  PixelFormat GetDefaultGlyphAtlasFormat() const override;
+
  private:
   bool supports_framebuffer_fetch_ = false;
   bool supports_decal_sampler_address_mode_ = false;
   bool supports_offscreen_msaa_ = false;
   bool supports_implicit_msaa_ = false;
+
+  PixelFormat default_glyph_atlas_format_ = PixelFormat::kUnknown;
 };
 
 }  // namespace impeller

impeller/renderer/backend/metal/context_mtl.mm

@@ -67,6 +67,7 @@ static bool DeviceSupportsComputeSubgroups(id<MTLDevice> device) {
       .SetSupportsComputeSubgroups(DeviceSupportsComputeSubgroups(device))
       .SetSupportsReadFromResolve(true)
       .SetSupportsDeviceTransientTextures(true)
+      .SetDefaultGlyphAtlasFormat(PixelFormat::kA8UNormInt)
       .Build();
 }
 

impeller/renderer/backend/vulkan/capabilities_vk.cc

@@ -484,4 +484,8 @@ bool CapabilitiesVK::HasOptionalDeviceExtension(
          optional_device_extensions_.end();
 }
 
+PixelFormat CapabilitiesVK::GetDefaultGlyphAtlasFormat() const {
+  return PixelFormat::kR8UNormInt;
+}
+
 }  // namespace impeller

impeller/renderer/backend/vulkan/capabilities_vk.h

@@ -100,6 +100,9 @@ class CapabilitiesVK final : public Capabilities,
   // |Capabilities|
   PixelFormat GetDefaultDepthStencilFormat() const override;
 
+  // |Capabilities|
+  PixelFormat GetDefaultGlyphAtlasFormat() const override;
+
  private:
   bool validations_enabled_ = false;
   std::map<std::string, std::set<std::string>> exts_;

impeller/renderer/capabilities_unittests.cc

@@ -31,31 +31,40 @@ CAPABILITY_TEST(SupportsDeviceTransientTextures, false);
 
 TEST(CapabilitiesTest, DefaultColorFormat) {
   auto defaults = CapabilitiesBuilder().Build();
-  ASSERT_EQ(defaults->GetDefaultColorFormat(), PixelFormat::kUnknown);
+  EXPECT_EQ(defaults->GetDefaultColorFormat(), PixelFormat::kUnknown);
   auto mutated = CapabilitiesBuilder()
                      .SetDefaultColorFormat(PixelFormat::kB10G10R10A10XR)
                      .Build();
-  ASSERT_EQ(mutated->GetDefaultColorFormat(), PixelFormat::kB10G10R10A10XR);
+  EXPECT_EQ(mutated->GetDefaultColorFormat(), PixelFormat::kB10G10R10A10XR);
 }
 
 TEST(CapabilitiesTest, DefaultStencilFormat) {
   auto defaults = CapabilitiesBuilder().Build();
-  ASSERT_EQ(defaults->GetDefaultStencilFormat(), PixelFormat::kUnknown);
+  EXPECT_EQ(defaults->GetDefaultStencilFormat(), PixelFormat::kUnknown);
   auto mutated = CapabilitiesBuilder()
                      .SetDefaultStencilFormat(PixelFormat::kS8UInt)
                      .Build();
-  ASSERT_EQ(mutated->GetDefaultStencilFormat(), PixelFormat::kS8UInt);
+  EXPECT_EQ(mutated->GetDefaultStencilFormat(), PixelFormat::kS8UInt);
 }
 
 TEST(CapabilitiesTest, DefaultDepthStencilFormat) {
   auto defaults = CapabilitiesBuilder().Build();
-  ASSERT_EQ(defaults->GetDefaultDepthStencilFormat(), PixelFormat::kUnknown);
+  EXPECT_EQ(defaults->GetDefaultDepthStencilFormat(), PixelFormat::kUnknown);
   auto mutated = CapabilitiesBuilder()
                      .SetDefaultDepthStencilFormat(PixelFormat::kD32FloatS8UInt)
                      .Build();
-  ASSERT_EQ(mutated->GetDefaultDepthStencilFormat(),
+  EXPECT_EQ(mutated->GetDefaultDepthStencilFormat(),
             PixelFormat::kD32FloatS8UInt);
 }
 
+TEST(CapabilitiesTest, DefaultGlyphAtlasFormat) {
+  auto defaults = CapabilitiesBuilder().Build();
+  EXPECT_EQ(defaults->GetDefaultGlyphAtlasFormat(), PixelFormat::kUnknown);
+  auto mutated = CapabilitiesBuilder()
+                     .SetDefaultGlyphAtlasFormat(PixelFormat::kA8UNormInt)
+                     .Build();
+  EXPECT_EQ(mutated->GetDefaultGlyphAtlasFormat(), PixelFormat::kA8UNormInt);
+}
+
 }  // namespace testing
 }  // namespace impeller