wip texture format.

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 = value.rrrr * v_text_color;
+  frag_color = max(value.rrrr, value.aaaa) * v_text_color;
 }

impeller/renderer/capabilities.cc

@@ -3,6 +3,7 @@
 // found in the LICENSE file.
 
 #include "impeller/renderer/capabilities.h"
+#include "impeller/core/formats.h"
 
 namespace impeller {
 
@@ -74,10 +75,16 @@ class StandardCapabilities final : public Capabilities {
     return default_depth_stencil_format_;
   }
 
+  // |Capabilities|
   bool SupportsDeviceTransientTextures() const override {
     return supports_device_transient_textures_;
   }
 
+  // |Capabilities|
+  PixelFormat GetDefaultGlyphAtlasFormat() const override {
+    return default_glyph_atlas_format_;
+  }
+
  private:
   StandardCapabilities(bool supports_offscreen_msaa,
                        bool supports_ssbo,
@@ -91,7 +98,8 @@ class StandardCapabilities final : public Capabilities {
                        bool supports_device_transient_textures,
                        PixelFormat default_color_format,
                        PixelFormat default_stencil_format,
-                       PixelFormat default_depth_stencil_format)
+                       PixelFormat default_depth_stencil_format,
+                       PixelFormat default_glyph_atlas_format)
       : supports_offscreen_msaa_(supports_offscreen_msaa),
         supports_ssbo_(supports_ssbo),
         supports_buffer_to_texture_blits_(supports_buffer_to_texture_blits),
@@ -122,6 +130,7 @@ class StandardCapabilities final : public Capabilities {
   PixelFormat default_color_format_ = PixelFormat::kUnknown;
   PixelFormat default_stencil_format_ = PixelFormat::kUnknown;
   PixelFormat default_depth_stencil_format_ = PixelFormat::kUnknown;
+  PixelFormat default_glyph_atlas_format_ = PixelFormat::kUnknown;
 
   StandardCapabilities(const StandardCapabilities&) = delete;
 
@@ -207,6 +216,12 @@ CapabilitiesBuilder& CapabilitiesBuilder::SetSupportsDeviceTransientTextures(
   return *this;
 }
 
+CapabilitiesBuilder& CapabilitiesBuilder::SetDefaultGlyphAtlasFormat(
+    PixelFormat value) {
+  default_glyph_atlas_format_ = value;
+  return *this;
+}
+
 std::unique_ptr<Capabilities> CapabilitiesBuilder::Build() {
   return std::unique_ptr<StandardCapabilities>(new StandardCapabilities(  //
       supports_offscreen_msaa_,                                           //
@@ -221,7 +236,8 @@ std::unique_ptr<Capabilities> CapabilitiesBuilder::Build() {
       supports_device_transient_textures_,                                //
       default_color_format_.value_or(PixelFormat::kUnknown),              //
       default_stencil_format_.value_or(PixelFormat::kUnknown),            //
-      default_depth_stencil_format_.value_or(PixelFormat::kUnknown)       //
+      default_depth_stencil_format_.value_or(PixelFormat::kUnknown),      //
+      default_glyph_atlas_format_.value_or(PixelFormat::kUnknown)         //
       ));
 }
 

impeller/renderer/capabilities.h

@@ -105,6 +105,12 @@ class Capabilities {
   ///         format was found.
   virtual PixelFormat GetDefaultDepthStencilFormat() const = 0;
 
+  /// @brief Returns the default pixel format for the alpha bitmap glyph atlas.
+  ///
+  ///        Some backends may use Red channel while others use grey. This
+  ///        should not have any impact
+  virtual PixelFormat GetDefaultGlyphAtlasFormat() const = 0;
+
  protected:
   Capabilities();
 
@@ -145,6 +151,8 @@ class CapabilitiesBuilder {
 
   CapabilitiesBuilder& SetSupportsDeviceTransientTextures(bool value);
 
+  CapabilitiesBuilder& SetDefaultGlyphAtlasFormat(PixelFormat value);
+
   std::unique_ptr<Capabilities> Build();
 
  private:
@@ -161,6 +169,7 @@ class CapabilitiesBuilder {
   std::optional<PixelFormat> default_color_format_ = std::nullopt;
   std::optional<PixelFormat> default_stencil_format_ = std::nullopt;
   std::optional<PixelFormat> default_depth_stencil_format_ = std::nullopt;
+  std::optional<PixelFormat> default_glyph_atlas_format_ = std::nullopt;
 
   CapabilitiesBuilder(const CapabilitiesBuilder&) = delete;
 

impeller/typographer/backends/skia/typographer_context_skia.cc

@@ -122,12 +122,12 @@ static ISize OptimumAtlasSizeForFontGlyphPairs(
     GlyphAtlas::Type type,
     const ISize& max_texture_size) {
   static constexpr auto kMinAtlasSize = 8u;
-  static constexpr auto kMinRedBitmapSize = 1024u;
+  static constexpr auto kMinAlphaBitmapSize = 1024u;
 
   TRACE_EVENT0("impeller", __FUNCTION__);
 
-  ISize current_size = type == GlyphAtlas::Type::kRedBitmap
-                           ? ISize(kMinRedBitmapSize, kMinRedBitmapSize)
+  ISize current_size = type == GlyphAtlas::Type::kAlphaBitmap
+                           ? ISize(kMinAlphaBitmapSize, kMinAlphaBitmapSize)
                            : ISize(kMinAtlasSize, kMinAtlasSize);
   size_t total_pairs = pairs.size() + 1;
   do {
@@ -171,7 +171,7 @@ static void DrawGlyph(SkCanvas* canvas,
   sk_font.setHinting(SkFontHinting::kSlight);
   sk_font.setEmbolden(metrics.embolden);
 
-  auto glyph_color = has_color ? SK_ColorWHITE : SK_ColorRED;
+  auto glyph_color = has_color ? SK_ColorWHITE : SK_ColorBLACK;
 
   SkPaint glyph_paint;
   glyph_paint.setColor(glyph_color);
@@ -221,11 +221,10 @@ static std::shared_ptr<SkBitmap> CreateAtlasBitmap(const GlyphAtlas& atlas,
   SkImageInfo image_info;
 
   switch (atlas.GetType()) {
-    case GlyphAtlas::Type::kRedBitmap:
+    case GlyphAtlas::Type::kAlphaBitmap:
       image_info =
-          SkImageInfo::Make(SkISize{static_cast<int32_t>(atlas_size.width),
-                                    static_cast<int32_t>(atlas_size.height)},
-                            kR8_unorm_SkColorType, kPremul_SkAlphaType);
+          SkImageInfo::MakeA8(SkISize{static_cast<int32_t>(atlas_size.width),
+                                      static_cast<int32_t>(atlas_size.height)});
       break;
     case GlyphAtlas::Type::kColorBitmap:
       image_info =
@@ -470,7 +469,7 @@ std::shared_ptr<GlyphAtlas> TypographerContextSkia::CreateGlyphAtlas(
   // ---------------------------------------------------------------------------
   PixelFormat format;
   switch (type) {
-    case GlyphAtlas::Type::kRedBitmap:
+    case GlyphAtlas::Type::kAlphaBitmap:
       format = PixelFormat::kR8UNormInt;
       break;
     case GlyphAtlas::Type::kColorBitmap:

impeller/typographer/backends/stb/typographer_context_stb.cc

@@ -163,12 +163,12 @@ static ISize OptimumAtlasSizeForFontGlyphPairs(
     GlyphAtlas::Type type,
     const ISize& max_texture_size) {
   static constexpr auto kMinAtlasSize = 8u;
-  static constexpr auto kMinRedBitmapSize = 1024u;
+  static constexpr auto kMinAlphaBitmapSize = 1024u;
 
   TRACE_EVENT0("impeller", __FUNCTION__);
 
-  ISize current_size = type == GlyphAtlas::Type::kRedBitmap
-                           ? ISize(kMinRedBitmapSize, kMinRedBitmapSize)
+  ISize current_size = type == GlyphAtlas::Type::kAlphaBitmap
+                           ? ISize(kMinAlphaBitmapSize, kMinAlphaBitmapSize)
                            : ISize(kMinAtlasSize, kMinAtlasSize);
   size_t total_pairs = pairs.size() + 1;
   do {
@@ -515,7 +515,7 @@ std::shared_ptr<GlyphAtlas> TypographerContextSTB::CreateGlyphAtlas(
   // ---------------------------------------------------------------------------
   PixelFormat format;
   switch (type) {
-    case GlyphAtlas::Type::kRedBitmap:
+    case GlyphAtlas::Type::kAlphaBitmap:
       format = PixelFormat::kR8UNormInt;
       break;
     case GlyphAtlas::Type::kColorBitmap:

impeller/typographer/glyph_atlas.h

@@ -10,7 +10,6 @@
 #include <optional>
 #include <unordered_map>
 
-#include "flutter/fml/macros.h"
 #include "impeller/core/texture.h"
 #include "impeller/geometry/rect.h"
 #include "impeller/renderer/pipeline.h"
@@ -33,9 +32,9 @@ class GlyphAtlas {
   enum class Type {
     //--------------------------------------------------------------------------
     /// The glyphs are reprsented at their requested size using only an 8-bit
-    /// red channel.
+    /// alpha or red channel.
     ///
-    kRedBitmap,
+    kAlphaBitmap,
 
     //--------------------------------------------------------------------------
     /// The glyphs are reprsented at their requested size using N32 premul