Add explicit scaling methods for Point/Vector2 (flutter#119)

Author: bdero

impeller/aiks/canvas.cc

@@ -80,6 +80,10 @@ void Canvas::Translate(const Vector3& offset) {
   Concat(Matrix::MakeTranslation(offset));
 }
 
+void Canvas::Scale(const Vector2& scale) {
+  Concat(Matrix::MakeScale(scale));
+}
+
 void Canvas::Scale(const Vector3& scale) {
   Concat(Matrix::MakeScale(scale));
 }
@@ -283,7 +287,7 @@ void Canvas::DrawTextFrame(TextFrame text_frame, Point position, Paint paint) {
   auto text_contents = std::make_shared<TextContents>();
   text_contents->SetTextFrame(std::move(text_frame));
   text_contents->SetGlyphAtlas(std::move(lazy_glyph_atlas));
-  text_contents->SetColor(paint.color.Premultiply());
+  text_contents->SetColor(paint.color);
 
   Entity entity;
   entity.SetTransformation(GetCurrentTransformation() *

impeller/aiks/canvas.h

@@ -52,6 +52,8 @@ class Canvas {
 
   void Translate(const Vector3& offset);
 
+  void Scale(const Vector2& scale);
+
   void Scale(const Vector3& scale);
 
   void Skew(Scalar sx, Scalar sy);

impeller/entity/contents/text_contents.cc

@@ -80,7 +80,7 @@ bool TextContents::Render(const ContentContext& renderer,
   frame_info.atlas_size =
       Point{static_cast<Scalar>(atlas->GetTexture()->GetSize().width),
             static_cast<Scalar>(atlas->GetTexture()->GetSize().height)};
-  frame_info.text_color = ToVector(color_);
+  frame_info.text_color = ToVector(color_.Premultiply());
   VS::BindFrameInfo(cmd, pass.GetTransientsBuffer().EmplaceUniform(frame_info));
 
   // Common fragment uniforms for all glyphs.

impeller/geometry/geometry_unittests.cc

@@ -37,13 +37,24 @@ TEST(GeometryTest, RotationMatrix) {
 }
 
 TEST(GeometryTest, InvertMultMatrix) {
-  auto rotation = Matrix::MakeRotationZ(Radians{M_PI_4});
-  auto invert = rotation.Invert();
-  auto expect = Matrix{0.707, -0.707, 0, 0,  //
-                       0.707, 0.707,  0, 0,  //
-                       0,     0,      1, 0,  //
-                       0,     0,      0, 1};
-  ASSERT_MATRIX_NEAR(invert, expect);
+  {
+    auto rotation = Matrix::MakeRotationZ(Radians{M_PI_4});
+    auto invert = rotation.Invert();
+    auto expect = Matrix{0.707, -0.707, 0, 0,  //
+                         0.707, 0.707,  0, 0,  //
+                         0,     0,      1, 0,  //
+                         0,     0,      0, 1};
+    ASSERT_MATRIX_NEAR(invert, expect);
+  }
+  {
+    auto scale = Matrix::MakeScale(Vector2{2, 4});
+    auto invert = scale.Invert();
+    auto expect = Matrix{0.5, 0,    0, 0,  //
+                         0,   0.25, 0, 0,  //
+                         0,   0,    1, 0,  //
+                         0,   0,    0, 1};
+    ASSERT_MATRIX_NEAR(invert, expect);
+  }
 }
 
 TEST(GeometryTest, MutliplicationMatrix) {

impeller/geometry/matrix.h

@@ -80,6 +80,10 @@ struct Matrix {
     // clang-format on
   }
 
+  static constexpr Matrix MakeScale(const Vector2& s) {
+    return MakeScale(Vector3(s.x, s.y, 1.0));
+  }
+
   static constexpr Matrix MakeSkew(Scalar sx, Scalar sy) {
     // clang-format off
     return Matrix(1.0, sy , 0.0, 0.0,