[Impeller] Fix the source rectangle used when rendering an AtlasContents with the strict mode for nine-patch images (flutter#177860)

* Convert the source rectangle to texture coordinates and shrink it to
adjust for linear filtering
* Pass the coordinates of the rectangle in the order expected by the
Porter-Duff shader

Fixes flutter#176544

Author: jason-simmons

engine/src/flutter/impeller/display_list/dl_unittests.cc

@@ -809,6 +809,22 @@ TEST_P(DisplayListTest, NinePatchImagePrecision) {
   ASSERT_TRUE(OpenPlaygroundHere(builder.Build()));
 }
 
+TEST_P(DisplayListTest, NinePatchImageColorFilter) {
+  auto texture = CreateTextureForFixture("nine_patch2.png");
+
+  auto filter = flutter::DlColorFilter::MakeBlend(flutter::DlColor::kGreen(),
+                                                  flutter::DlBlendMode::kSrcIn);
+  flutter::DlPaint paint;
+  paint.setColorFilter(filter);
+
+  flutter::DisplayListBuilder builder;
+  builder.DrawImageNine(DlImageImpeller::Make(texture),
+                        DlIRect::MakeXYWH(10, 10, 1, 1),
+                        DlRect::MakeXYWH(0, 0, 200, 100),
+                        flutter::DlFilterMode::kNearest, &paint);
+  ASSERT_TRUE(OpenPlaygroundHere(builder.Build()));
+}
+
 TEST_P(DisplayListTest, CanDrawPoints) {
   flutter::DisplayListBuilder builder;
   DlPoint points[7] = {

engine/src/flutter/impeller/entity/contents/atlas_contents.cc

@@ -127,7 +127,10 @@ bool DrawImageRectAtlasGeometry::ShouldInvertBlendMode() const {
 
 std::optional<Rect> DrawImageRectAtlasGeometry::GetStrictSrcRect() const {
   if (use_strict_src_rect_) {
-    return source_;
+    // For a strict source rect, shrink the texture coordinate range by half a
+    // texel to ensure that linear filtering does not sample anything outside
+    // the source rect bounds.
+    return Rect::MakeSize(texture_->GetSize()).Project(source_.Expand(-0.5));
   }
   return std::nullopt;
 }
@@ -230,8 +233,8 @@ bool AtlasContents::Render(const ContentContext& renderer,
     if (auto rect = geometry_->GetStrictSrcRect(); rect.has_value()) {
       Rect src_rect = rect.value();
       frag_info.source_rect =
-          Vector4(src_rect.GetX(), src_rect.GetY(), src_rect.GetBottom(),
-                  src_rect.GetRight());
+          Vector4(src_rect.GetX(), src_rect.GetY(), src_rect.GetRight(),
+                  src_rect.GetBottom());
       frag_info.use_strict_source_rect = 1.0;
     } else {
       frag_info.use_strict_source_rect = 0.0;

engine/src/flutter/impeller/entity/contents/atlas_contents.h

@@ -40,8 +40,8 @@ class AtlasGeometry {
 
   virtual bool ShouldInvertBlendMode() const { return true; }
 
-  /// @brief The source rect of the draw if a strict source rect should
-  ///        be applied, or nullopt.
+  /// @brief The source rect of the draw in texture coordinates if a strict
+  ///        source rect should be applied, or nullopt.
   ///
   /// See also `Canvas::AttemptColorFilterOptimization`
   virtual std::optional<Rect> GetStrictSrcRect() const { return std::nullopt; }

engine/src/flutter/impeller/fixtures/BUILD.gn

@@ -130,6 +130,7 @@ test_fixtures("file_fixtures") {
     "monkey.png",
     "multiple_stages.hlsl",
     "nine_patch_corners.png",
+    "nine_patch2.png",
     "resources_limit.vert",
     "sample.comp",
     "sample.frag",