Reland: Update Color to do all calculations with floating point components

flutter_frontend_server/test/to_string_test.dart

@@ -60,7 +60,8 @@ void main() {
     ]));
     final runResult = io.Process.runSync(dart, <String>[regularDill]);
     checkProcessResult(runResult);
-    var paintString = '"Paint.toString":"Paint(Color(0xffffffff))"';
+    var paintString =
+      '"Paint.toString":"Paint(Color(alpha: 1.0000, red: 1.0000, green: 1.0000, blue: 1.0000, colorSpace: ColorSpace.sRGB))"';
     if (buildDir.contains('release')) {
       paintString = '"Paint.toString":"Instance of \'Paint\'"';
     }

lib/ui/lerp.dart

@@ -37,15 +37,3 @@ double _lerpDouble(double a, double b, double t) {
 double _lerpInt(int a, int b, double t) {
   return a + (b - a) * t;
 }
-
-/// Same as [num.clamp] but specialized for non-null [int].
-int _clampInt(int value, int min, int max) {
-  assert(min <= max);
-  if (value < min) {
-    return min;
-  } else if (value > max) {
-    return max;
-  } else {
-    return value;
-  }
-}

lib/ui/painting.dart

@@ -48,8 +48,8 @@ bool _radiusIsValid(Radius radius) {
   return true;
 }
 
-Color _scaleAlpha(Color a, double factor) {
-  return a.withAlpha((a.alpha * factor).round().clamp(0, 255));
+Color _scaleAlpha(Color x, double factor) {
+  return x.withValues(alpha: clampDouble(x.a * factor, 0, 1));
 }
 
 /// An immutable 32 bit color value in ARGB format.
@@ -310,10 +310,11 @@ class Color {
   ///
   /// See <https://en.wikipedia.org/wiki/Relative_luminance>.
   double computeLuminance() {
+    assert(colorSpace != ColorSpace.extendedSRGB);
     // See <https://www.w3.org/TR/WCAG20/#relativeluminancedef>
-    final double R = _linearizeColorComponent(red / 0xFF);
-    final double G = _linearizeColorComponent(green / 0xFF);
-    final double B = _linearizeColorComponent(blue / 0xFF);
+    final double R = _linearizeColorComponent(r);
+    final double G = _linearizeColorComponent(g);
+    final double B = _linearizeColorComponent(b);
     return 0.2126 * R + 0.7152 * G + 0.0722 * B;
   }
 
@@ -339,28 +340,26 @@ class Color {
   ///
   /// Values for `t` are usually obtained from an [Animation<double>], such as
   /// an [AnimationController].
-  static Color? lerp(Color? a, Color? b, double t) {
-    // TODO(gaaclarke): Update math to use floats. This was already attempted
-    //                  but it leads to subtle changes that change test results.
-    assert(a?.colorSpace != ColorSpace.extendedSRGB);
-    assert(b?.colorSpace != ColorSpace.extendedSRGB);
-    if (b == null) {
-      if (a == null) {
+  static Color? lerp(Color? x, Color? y, double t) {
+    assert(x?.colorSpace != ColorSpace.extendedSRGB);
+    assert(y?.colorSpace != ColorSpace.extendedSRGB);
+    if (y == null) {
+      if (x == null) {
         return null;
       } else {
-        return _scaleAlpha(a, 1.0 - t);
+        return _scaleAlpha(x, 1.0 - t);
       }
     } else {
-      if (a == null) {
-        return _scaleAlpha(b, t);
+      if (x == null) {
+        return _scaleAlpha(y, t);
       } else {
-        assert(a.colorSpace == b.colorSpace);
-        return Color._fromARGBC(
-          _clampInt(_lerpInt(a.alpha, b.alpha, t).toInt(), 0, 255),
-          _clampInt(_lerpInt(a.red, b.red, t).toInt(), 0, 255),
-          _clampInt(_lerpInt(a.green, b.green, t).toInt(), 0, 255),
-          _clampInt(_lerpInt(a.blue, b.blue, t).toInt(), 0, 255),
-          a.colorSpace,
+        assert(x.colorSpace == y.colorSpace);
+        return Color.from(
+          alpha: clampDouble(_lerpDouble(x.a, y.a, t), 0, 1),
+          red: clampDouble(_lerpDouble(x.r, y.r, t), 0, 1),
+          green: clampDouble(_lerpDouble(x.g, y.g, t), 0, 1),
+          blue: clampDouble(_lerpDouble(x.b, y.b, t), 0, 1),
+          colorSpace: x.colorSpace,
         );
       }
     }
@@ -377,32 +376,30 @@ class Color {
   static Color alphaBlend(Color foreground, Color background) {
     assert(foreground.colorSpace == background.colorSpace);
     assert(foreground.colorSpace != ColorSpace.extendedSRGB);
-    // TODO(gaaclarke): Update math to use floats. This was already attempted
-    //                  but it leads to subtle changes that change test results.
-    final int alpha = foreground.alpha;
-    if (alpha == 0x00) { // Foreground completely transparent.
+    final double alpha = foreground.a;
+    if (alpha == 0) { // Foreground completely transparent.
       return background;
     }
-    final int invAlpha = 0xff - alpha;
-    int backAlpha = background.alpha;
-    if (backAlpha == 0xff) { // Opaque background case
-      return Color._fromARGBC(
-        0xff,
-        (alpha * foreground.red + invAlpha * background.red) ~/ 0xff,
-        (alpha * foreground.green + invAlpha * background.green) ~/ 0xff,
-        (alpha * foreground.blue + invAlpha * background.blue) ~/ 0xff,
-        foreground.colorSpace,
+    final double invAlpha = 1 - alpha;
+    double backAlpha = background.a;
+    if (backAlpha == 1) { // Opaque background case
+      return Color.from(
+        alpha: 1,
+        red: alpha * foreground.r + invAlpha * background.r,
+        green: alpha * foreground.g + invAlpha * background.g,
+        blue: alpha * foreground.b + invAlpha * background.b,
+        colorSpace: foreground.colorSpace,
       );
     } else { // General case
-      backAlpha = (backAlpha * invAlpha) ~/ 0xff;
-      final int outAlpha = alpha + backAlpha;
-      assert(outAlpha != 0x00);
-      return Color._fromARGBC(
-        outAlpha,
-        (foreground.red * alpha + background.red * backAlpha) ~/ outAlpha,
-        (foreground.green * alpha + background.green * backAlpha) ~/ outAlpha,
-        (foreground.blue * alpha + background.blue * backAlpha) ~/ outAlpha,
-        foreground.colorSpace,
+      backAlpha = backAlpha * invAlpha;
+      final double outAlpha = alpha + backAlpha;
+      assert(outAlpha != 0);
+      return Color.from(
+        alpha: outAlpha,
+        red: (foreground.r * alpha + background.r * backAlpha) / outAlpha,
+        green: (foreground.g * alpha + background.g * backAlpha) / outAlpha,
+        blue: (foreground.b * alpha + background.b * backAlpha) / outAlpha,
+        colorSpace: foreground.colorSpace,
       );
     }
   }
@@ -423,16 +420,19 @@ class Color {
       return false;
     }
     return other is Color &&
-        other.value == value &&
+        other.a == a &&
+        other.r == r &&
+        other.g == g &&
+        other.b == b &&
         other.colorSpace == colorSpace;
   }
 
   @override
-  int get hashCode => Object.hash(value, colorSpace);
+  int get hashCode => Object.hash(a, r, g, b, colorSpace);
 
-  // TODO(gaaclarke): Make toString() print out float values.
   @override
-  String toString() => 'Color(0x${value.toRadixString(16).padLeft(8, '0')})';
+  String toString() =>
+      'Color(alpha: ${a.toStringAsFixed(4)}, red: ${r.toStringAsFixed(4)}, green: ${g.toStringAsFixed(4)}, blue: ${b.toStringAsFixed(4)}, colorSpace: $colorSpace)';
 }
 
 /// Algorithms to use when painting on the canvas.

lib/web_ui/lib/lerp.dart

@@ -28,10 +28,3 @@ double? lerpDouble(num? a, num? b, double t) {
 double _lerpDouble(double a, double b, double t) {
   return a * (1.0 - t) + b * t;
 }
-
-/// Linearly interpolate between two integers.
-///
-/// Same as [lerpDouble] but specialized for non-null `int` type.
-double _lerpInt(int a, int b, double t) {
-  return a * (1.0 - t) + b * t;
-}

lib/web_ui/lib/painting.dart

@@ -17,8 +17,8 @@ void _validateColorStops(List<Color> colors, List<double>? colorStops) {
   }
 }
 
-Color _scaleAlpha(Color a, double factor) {
-  return a.withAlpha(engine.clampInt((a.alpha * factor).round(), 0, 255));
+Color _scaleAlpha(Color x, double factor) {
+  return x.withValues(alpha: (x.a * factor).clamp(0, 1));
 }
 
 class Color {
@@ -141,32 +141,32 @@ class Color {
 
   double computeLuminance() {
     // See <https://www.w3.org/TR/WCAG20/#relativeluminancedef>
-    final double R = _linearizeColorComponent(red / 0xFF);
-    final double G = _linearizeColorComponent(green / 0xFF);
-    final double B = _linearizeColorComponent(blue / 0xFF);
+    final double R = _linearizeColorComponent(r);
+    final double G = _linearizeColorComponent(g);
+    final double B = _linearizeColorComponent(b);
     return 0.2126 * R + 0.7152 * G + 0.0722 * B;
   }
 
-  static Color? lerp(Color? a, Color? b, double t) {
-    assert(a?.colorSpace != ColorSpace.extendedSRGB);
-    assert(b?.colorSpace != ColorSpace.extendedSRGB);
-    if (b == null) {
-      if (a == null) {
+  static Color? lerp(Color? x, Color? y, double t) {
+    assert(x?.colorSpace != ColorSpace.extendedSRGB);
+    assert(y?.colorSpace != ColorSpace.extendedSRGB);
+    if (y == null) {
+      if (x == null) {
         return null;
       } else {
-        return _scaleAlpha(a, 1.0 - t);
+        return _scaleAlpha(x, 1.0 - t);
       }
     } else {
-      if (a == null) {
-        return _scaleAlpha(b, t);
+      if (x == null) {
+        return _scaleAlpha(y, t);
       } else {
-        assert(a.colorSpace == b.colorSpace);
-        return Color._fromARGBC(
-          engine.clampInt(_lerpInt(a.alpha, b.alpha, t).toInt(), 0, 255),
-          engine.clampInt(_lerpInt(a.red, b.red, t).toInt(), 0, 255),
-          engine.clampInt(_lerpInt(a.green, b.green, t).toInt(), 0, 255),
-          engine.clampInt(_lerpInt(a.blue, b.blue, t).toInt(), 0, 255),
-          a.colorSpace,
+        assert(x.colorSpace == y.colorSpace);
+        return Color.from(
+          alpha: _lerpDouble(x.a, y.a, t).clamp(0, 1),
+          red: _lerpDouble(x.r, y.r, t).clamp(0, 1),
+          green: _lerpDouble(x.g, y.g, t).clamp(0, 1),
+          blue: _lerpDouble(x.b, y.b, t).clamp(0, 1),
+          colorSpace: x.colorSpace,
         );
       }
     }
@@ -175,30 +175,30 @@ class Color {
   static Color alphaBlend(Color foreground, Color background) {
     assert(foreground.colorSpace == background.colorSpace);
     assert(foreground.colorSpace != ColorSpace.extendedSRGB);
-    final int alpha = foreground.alpha;
-    if (alpha == 0x00) {
+    final double alpha = foreground.a;
+    if (alpha == 0) { // Foreground completely transparent.
       return background;
     }
-    final int invAlpha = 0xff - alpha;
-    int backAlpha = background.alpha;
-    if (backAlpha == 0xff) {
-      return Color._fromARGBC(
-        0xff,
-        (alpha * foreground.red + invAlpha * background.red) ~/ 0xff,
-        (alpha * foreground.green + invAlpha * background.green) ~/ 0xff,
-        (alpha * foreground.blue + invAlpha * background.blue) ~/ 0xff,
-        foreground.colorSpace,
+    final double invAlpha = 1 - alpha;
+    double backAlpha = background.a;
+    if (backAlpha == 1) { // Opaque background case
+      return Color.from(
+        alpha: 1,
+        red: alpha * foreground.r + invAlpha * background.r,
+        green: alpha * foreground.g + invAlpha * background.g,
+        blue: alpha * foreground.b + invAlpha * background.b,
+        colorSpace: foreground.colorSpace,
       );
-    } else {
-      backAlpha = (backAlpha * invAlpha) ~/ 0xff;
-      final int outAlpha = alpha + backAlpha;
-      assert(outAlpha != 0x00);
-      return Color._fromARGBC(
-        outAlpha,
-        (foreground.red * alpha + background.red * backAlpha) ~/ outAlpha,
-        (foreground.green * alpha + background.green * backAlpha) ~/ outAlpha,
-        (foreground.blue * alpha + background.blue * backAlpha) ~/ outAlpha,
-        foreground.colorSpace,
+    } else { // General case
+      backAlpha = backAlpha * invAlpha;
+      final double outAlpha = alpha + backAlpha;
+      assert(outAlpha != 0);
+      return Color.from(
+        alpha: outAlpha,
+        red: (foreground.r * alpha + background.r * backAlpha) / outAlpha,
+        green: (foreground.g * alpha + background.g * backAlpha) / outAlpha,
+        blue: (foreground.b * alpha + background.b * backAlpha) / outAlpha,
+        colorSpace: foreground.colorSpace,
       );
     }
   }
@@ -216,15 +216,19 @@ class Color {
       return false;
     }
     return other is Color &&
-        other.value == value &&
+        other.a == a &&
+        other.r == r &&
+        other.g == g &&
+        other.b == b &&
         other.colorSpace == colorSpace;
   }
 
   @override
-  int get hashCode => Object.hash(value, colorSpace);
+  int get hashCode => Object.hash(a, r, g, b, colorSpace);
 
   @override
-  String toString() => 'Color(0x${value.toRadixString(16).padLeft(8, '0')})';
+  String toString() =>
+      'Color(alpha: ${a.toStringAsFixed(4)}, red: ${r.toStringAsFixed(4)}, green: ${g.toStringAsFixed(4)}, blue: ${b.toStringAsFixed(4)}, colorSpace: $colorSpace)';
 }
 
 enum StrokeCap {