colormatrix is now 0...1 (#8772)

* colormatrix is now 0...1

* reformat

lib/ui/painting/paint.cc

@@ -52,7 +52,7 @@ constexpr double kStrokeMiterLimitDefault = 4.0;
 
 // A color matrix which inverts colors.
 // clang-format off
-constexpr SkScalar invert_colors[20] = {
+constexpr float invert_colors[20] = {
   -1.0,    0,    0, 1.0, 0,
      0, -1.0,    0, 1.0, 0,
      0,    0, -1.0, 1.0, 0,
@@ -72,6 +72,19 @@ enum ColorFilterType {
   SRGBToLinearGamma
 };
 
+// Flutter still defines the matrix to be biased by 255 in the last column
+// (translate). skia is normalized, treating the last column as 0...1, so we
+// post-scale here before calling the skia factory.
+static sk_sp<SkColorFilter> MakeColorMatrixFilter255(const float array[20]) {
+  float tmp[20];
+  memcpy(tmp, array, sizeof(tmp));
+  tmp[4] *= 1.0f / 255;
+  tmp[9] *= 1.0f / 255;
+  tmp[14] *= 1.0f / 255;
+  tmp[19] *= 1.0f / 255;
+  return SkColorFilters::Matrix(tmp);
+}
+
 sk_sp<SkColorFilter> ExtractColorFilter(const uint32_t* uint_data,
                                         Dart_Handle* values) {
   switch (uint_data[kColorFilterIndex]) {
@@ -92,7 +105,7 @@ sk_sp<SkColorFilter> ExtractColorFilter(const uint32_t* uint_data,
         FML_CHECK(length == 20);
 
         tonic::Float32List decoded(matrixHandle);
-        return SkColorFilters::MatrixRowMajor255(decoded.data());
+        return MakeColorMatrixFilter255(decoded.data());
       }
       return nullptr;
     }
@@ -178,11 +191,11 @@ Paint::Paint(Dart_Handle paint_objects, Dart_Handle paint_data) {
     sk_sp<SkColorFilter> color_filter = ExtractColorFilter(uint_data, values);
     if (color_filter) {
       sk_sp<SkColorFilter> invert_filter =
-          SkColorFilters::MatrixRowMajor255(invert_colors);
+          MakeColorMatrixFilter255(invert_colors);
       paint_.setColorFilter(invert_filter->makeComposed(color_filter));
     }
   } else if (uint_data[kInvertColorIndex]) {
-    paint_.setColorFilter(SkColorFilters::MatrixRowMajor255(invert_colors));
+    paint_.setColorFilter(MakeColorMatrixFilter255(invert_colors));
   } else if (uint_data[kColorFilterIndex]) {
     sk_sp<SkColorFilter> color_filter = ExtractColorFilter(uint_data, values);
     if (color_filter) {