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Color.opacity

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Sometimes you want the alpha channel as a double rather than an int.
For convenience, provide an accessor on Color that returns this.
This commit is contained in:
Ian Hickson 2016-01-15 23:28:13 -08:00
parent 7cd13f1d27
commit e423d48ebf
1 changed files with 10 additions and 7 deletions
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17
sky/engine/core/painting/Color.dart
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@ -10,7 +10,7 @@ Color _scaleAlpha(Color a, double factor) {
/// An immutable 32 bit color value in ARGB
class Color {
/// Construct a color from the lower 32 bits of an int
/// Construct a color from the lower 32 bits of an int.
///
/// Bits 24-31 are the alpha value.
/// Bits 16-23 are the red value.
@ -25,25 +25,28 @@ class Color {
((g & 0xff) << 8) |
((b & 0xff) << 0)) & 0xFFFFFFFF);
final int _value;
/// A 32 bit value representing this color
/// A 32 bit value representing this color.
///
/// Bits 24-31 are the alpha value.
/// Bits 16-23 are the red value.
/// Bits 8-15 are the green value.
/// Bits 0-7 are the blue value.
int get value => _value;
final int _value;
/// The alpha channel of this color in an 8 bit value
/// The alpha channel of this color in an 8 bit value.
int get alpha => (0xff000000 & _value) >> 24;
/// The red channel of this color in an 8 bit value
/// The alpha channel of this color as a double.
double get opacity => alpha / 0xFF;
/// The red channel of this color in an 8 bit value.
int get red => (0x00ff0000 & _value) >> 16;
/// The green channel of this color in an 8 bit value
/// The green channel of this color in an 8 bit value.
int get green => (0x0000ff00 & _value) >> 8;
/// The blue channel of this color in an 8 bit value
/// The blue channel of this color in an 8 bit value.
int get blue => (0x000000ff & _value) >> 0;
/// Returns a new color that matches this color with the alpha channel replaced with a.