Fixes rendering text rotated 180 degrees (#165008)

fixes flutter/flutter#164958

## Pre-launch Checklist

- [x] I read the [Contributor Guide] and followed the process outlined
there for submitting PRs.
- [x] I read the [Tree Hygiene] wiki page, which explains my
responsibilities.
- [x] I read and followed the [Flutter Style Guide], including [Features
we expect every widget to implement].
- [x] I signed the [CLA].
- [x] I listed at least one issue that this PR fixes in the description
above.
- [x] I updated/added relevant documentation (doc comments with `///`).
- [x] I added new tests to check the change I am making, or this PR is
[test-exempt].
- [x] I followed the [breaking change policy] and added [Data Driven
Fixes] where supported.
- [x] All existing and new tests are passing.

If you need help, consider asking for advice on the #hackers-new channel
on [Discord].

<!-- Links -->
[Contributor Guide]:
https://github.com/flutter/flutter/blob/main/docs/contributing/Tree-hygiene.md#overview
[Tree Hygiene]:
https://github.com/flutter/flutter/blob/main/docs/contributing/Tree-hygiene.md
[test-exempt]:
https://github.com/flutter/flutter/blob/main/docs/contributing/Tree-hygiene.md#tests
[Flutter Style Guide]:
https://github.com/flutter/flutter/blob/main/docs/contributing/Style-guide-for-Flutter-repo.md
[Features we expect every widget to implement]:
https://github.com/flutter/flutter/blob/main/docs/contributing/Style-guide-for-Flutter-repo.md#features-we-expect-every-widget-to-implement
[CLA]: https://cla.developers.google.com/
[flutter/tests]: https://github.com/flutter/tests
[breaking change policy]:
https://github.com/flutter/flutter/blob/main/docs/contributing/Tree-hygiene.md#handling-breaking-changes
[Discord]:
https://github.com/flutter/flutter/blob/main/docs/contributing/Chat.md
[Data Driven Fixes]:
https://github.com/flutter/flutter/blob/main/docs/contributing/Data-driven-Fixes.md

Author: gaaclarke

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

@@ -207,6 +207,44 @@ TEST_P(AiksTest, CanRenderTextFrameWithFractionScaling) {
   ASSERT_TRUE(OpenPlaygroundHere(callback));
 }
 
+// https://github.com/flutter/flutter/issues/164958
+TEST_P(AiksTest, TextRotated180Degrees) {
+  float fpivot[2] = {200 + 30, 200 - 20};
+  float rotation = 180;
+  float foffset[2] = {200, 200};
+
+  auto callback = [&]() -> sk_sp<DisplayList> {
+    if (AiksTest::ImGuiBegin("Controls", nullptr,
+                             ImGuiWindowFlags_AlwaysAutoResize)) {
+      ImGui::SliderFloat("pivotx", &fpivot[0], 0, 300);
+      ImGui::SliderFloat("pivoty", &fpivot[1], 0, 300);
+      ImGui::SliderFloat("rotation", &rotation, 0, 360);
+      ImGui::SliderFloat("foffsetx", &foffset[0], 0, 300);
+      ImGui::SliderFloat("foffsety", &foffset[1], 0, 300);
+      ImGui::End();
+    }
+    DisplayListBuilder builder;
+    builder.Scale(GetContentScale().x, GetContentScale().y);
+    builder.DrawPaint(DlPaint().setColor(DlColor(0xffffeeff)));
+
+    builder.Save();
+    DlPoint pivot = Point(fpivot[0], fpivot[1]);
+    builder.Translate(pivot.x, pivot.y);
+    builder.Rotate(rotation);
+    builder.Translate(-pivot.x, -pivot.y);
+
+    RenderTextInCanvasSkia(GetContext(), builder, "test", "Roboto-Regular.ttf",
+                           TextRenderOptions{
+                               .color = DlColor::kBlack(),
+                               .position = DlPoint(foffset[0], foffset[1]),
+                           });
+
+    builder.Restore();
+    return builder.Build();
+  };
+  ASSERT_TRUE(OpenPlaygroundHere(callback));
+}
+
 TEST_P(AiksTest, TextFrameSubpixelAlignment) {
   // "Random" numbers between 0 and 1. Hardcoded to avoid flakiness in goldens.
   std::array<Scalar, 20> phase_offsets = {

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

@@ -175,11 +175,12 @@ void TextContents::ComputeVertexData(
       Point uv_origin = (atlas_glyph_bounds.GetLeftTop()) / atlas_size;
       Point uv_size = SizeToPoint(atlas_glyph_bounds.GetSize()) / atlas_size;
 
+      Matrix unscaled_basis =
+          Matrix::MakeScale({basis_transform.m[0] > 0 ? 1.f : -1.f,
+                             basis_transform.m[5] > 0 ? 1.f : -1.f, 1.f});
       Point unrounded_glyph_position =
           // This is for RTL text.
-          (basis_transform.m[0] < 0 ? Matrix::MakeScale({-1, 1, 1})
-                                    : Matrix()) *
-              glyph_bounds.GetLeftTop() +
+          unscaled_basis * glyph_bounds.GetLeftTop() +
           (basis_transform * glyph_position.position);
 
       Point screen_glyph_position =
@@ -189,9 +190,7 @@ void TextContents::ComputeVertexData(
         Point position;
         if (is_translation_scale) {
           position = (screen_glyph_position +
-                      ((basis_transform.m[0] < 0 ? Matrix::MakeScale({-1, 1, 1})
-                                                 : Matrix()) *
-                       point * glyph_bounds.GetSize()))
+                      (unscaled_basis * point * glyph_bounds.GetSize()))
                          .Round();
         } else {
           position = entity_transform *

engine/src/flutter/testing/impeller_golden_tests_output.txt

@@ -919,6 +919,9 @@ impeller_Play_AiksTest_TextForegroundShaderWithTransform_Vulkan.png
 impeller_Play_AiksTest_TextFrameSubpixelAlignment_Metal.png
 impeller_Play_AiksTest_TextFrameSubpixelAlignment_OpenGLES.png
 impeller_Play_AiksTest_TextFrameSubpixelAlignment_Vulkan.png
+impeller_Play_AiksTest_TextRotated180Degrees_Metal.png
+impeller_Play_AiksTest_TextRotated180Degrees_OpenGLES.png
+impeller_Play_AiksTest_TextRotated180Degrees_Vulkan.png
 impeller_Play_AiksTest_ToImageFromImage_Metal.png
 impeller_Play_AiksTest_ToImageFromImage_OpenGLES.png
 impeller_Play_AiksTest_ToImageFromImage_Vulkan.png