Draw all glyphs in a text run using a single draw call. (flutter#97)

Author: chinmaygarde

impeller/entity/contents/text_contents.cc

@@ -67,7 +67,7 @@ bool TextContents::Render(const ContentContext& renderer,
 
   // Information shared by all glyph draw calls.
   Command cmd;
-  cmd.label = "Glyph";
+  cmd.label = "TextRun";
   cmd.primitive_type = PrimitiveType::kTriangle;
   cmd.pipeline =
       renderer.GetGlyphAtlasPipeline(OptionsFromPassAndEntity(pass, entity));
@@ -121,8 +121,20 @@ bool TextContents::Render(const ContentContext& renderer,
     cmd.BindVertices(std::move(vertex_buffer));
   }
 
+  size_t instance_count = 0u;
+  std::vector<Matrix> glyph_positions;
+  std::vector<Point> glyph_sizes;
+  std::vector<Point> atlas_positions;
+  std::vector<Point> atlas_glyph_sizes;
+
   // Iterate through all the runs in the blob.
   for (const auto& run : frame_.GetRuns()) {
+    instance_count = 0u;
+    glyph_positions.clear();
+    glyph_sizes.clear();
+    atlas_positions.clear();
+    atlas_glyph_sizes.clear();
+
     auto font = run.GetFont();
     auto glyph_size = ISize::Ceil(font.GetMetrics().GetBoundingBox().size);
     // Draw each glyph individually. This should probably be batched.
@@ -133,21 +145,29 @@ bool TextContents::Render(const ContentContext& renderer,
         VALIDATION_LOG << "Could not find glyph position in the atlas.";
         return false;
       }
+      instance_count++;
+      glyph_positions.emplace_back(glyph_position.position.Translate(
+          {font.GetMetrics().min_extent.x, font.GetMetrics().ascent, 0.0}));
+      glyph_sizes.emplace_back(Point{static_cast<Scalar>(glyph_size.width),
+                                     static_cast<Scalar>(glyph_size.height)});
+      atlas_positions.emplace_back(atlas_glyph_pos->origin);
+      atlas_glyph_sizes.emplace_back(
+          Point{atlas_glyph_pos->size.width, atlas_glyph_pos->size.height});
+    }
 
-      VS::GlyphInfo glyph_info;
-      glyph_info.position = glyph_position.position.Translate(
-          {font.GetMetrics().min_extent.x, font.GetMetrics().ascent, 0.0});
-      glyph_info.glyph_size = {static_cast<Scalar>(glyph_size.width),
-                               static_cast<Scalar>(glyph_size.height)};
-      glyph_info.atlas_position = atlas_glyph_pos->origin;
-      glyph_info.atlas_glyph_size = {atlas_glyph_pos->size.width,
-                                     atlas_glyph_pos->size.height};
-      VS::BindGlyphInfo(cmd,
-                        pass.GetTransientsBuffer().EmplaceUniform(glyph_info));
-
-      if (!pass.AddCommand(cmd)) {
-        return false;
-      }
+    cmd.instance_count = instance_count;
+    VS::BindGlyphPositions(
+        cmd, pass.GetTransientsBuffer().EmplaceStorageBuffer(glyph_positions));
+    VS::BindGlyphSizes(
+        cmd, pass.GetTransientsBuffer().EmplaceStorageBuffer(glyph_sizes));
+    VS::BindAtlasPositions(
+        cmd, pass.GetTransientsBuffer().EmplaceStorageBuffer(atlas_positions));
+    VS::BindAtlasGlyphSizes(
+        cmd,
+        pass.GetTransientsBuffer().EmplaceStorageBuffer(atlas_glyph_sizes));
+
+    if (!pass.AddCommand(cmd)) {
+      return false;
     }
   }
 

impeller/entity/shaders/glyph_atlas.vert

@@ -8,12 +8,21 @@ uniform FrameInfo {
   vec4 text_color;
 } frame_info;
 
-uniform GlyphInfo {
-  mat4 position;
-  vec2 glyph_size;
-  vec2 atlas_position;
-  vec2 atlas_glyph_size;
-} glyph_info;
+readonly buffer GlyphPositions {
+  mat4 position[];
+} glyph_positions;
+
+readonly buffer GlyphSizes {
+  vec2 size[];
+} glyph_sizes;
+
+readonly buffer AtlasPositions {
+  vec2 position[];
+} atlas_positions;
+
+readonly buffer AtlasGlyphSizes {
+  vec2 size[];
+} atlas_glyph_sizes;
 
 in vec2 unit_vertex;
 
@@ -24,20 +33,23 @@ out vec2 v_atlas_size;
 out vec4 v_text_color;
 
 void main() {
-  mat4 scale = mat4(
-    glyph_info.glyph_size.x, 0.0, 0.0, 0.0,
-    0.0, glyph_info.glyph_size.y, 0.0, 0.0,
-    0.0, 0.0, 1.0 , 0.0,
-    0.0, 0.0, 0.0 , 1.0
-  );
+  // The position to place the glyph.
+  mat4 glyph_position = glyph_positions.position[gl_InstanceIndex];
+  // The size of the glyph.
+  vec2 glyph_size = glyph_sizes.size[gl_InstanceIndex];
+  // The location of the glyph in the atlas.
+  vec2 glyph_atlas_position = atlas_positions.position[gl_InstanceIndex];
+  // The size of the glyph within the atlas.
+  vec2 glyph_atlas_size = atlas_glyph_sizes.size[gl_InstanceIndex];
+
   gl_Position = frame_info.mvp
-              * glyph_info.position
-              * scale
-              * vec4(unit_vertex, 0.0, 1.0);
+              * glyph_position
+              * vec4(unit_vertex.x * glyph_size.x,
+                     unit_vertex.y * glyph_size.y, 0.0, 1.0);
 
   v_unit_vertex = unit_vertex;
-  v_atlas_position = glyph_info.atlas_position;
-  v_atlas_glyph_size = glyph_info.atlas_glyph_size;
+  v_atlas_position = glyph_atlas_position;
+  v_atlas_glyph_size = glyph_atlas_size;
   v_atlas_size = frame_info.atlas_size;
   v_text_color = frame_info.text_color;
 }

impeller/renderer/backend/metal/render_pass_mtl.mm

@@ -399,6 +399,9 @@ static bool Bind(PassBindingsCache& pass,
     if (command.index_count == 0u) {
       continue;
     }
+    if (command.instance_count == 0u) {
+      continue;
+    }
 
     fml::ScopedCleanupClosure auto_pop_debug_marker(pop_debug_marker);
     if (!command.label.empty()) {
@@ -510,6 +513,12 @@ static bool Bind(PassBindingsCache& pass,
     return true;
   }
 
+  if (command.instance_count == 0u) {
+    // Essentially a no-op. Don't record the command but this is not necessary
+    // an error either.
+    return true;
+  }
+
   commands_.emplace_back(std::move(command));
   return true;
 }