Flutter 中渐变有三种：
LinearGradient：线性渐变 RadialGradient：放射状渐变 SweepGradient：扇形渐变看下原图，下面的渐变都是在此图基础上完成。
LinearGradient
给一张图片添加从上到下的线性渐变：
ShaderMask(
shaderCallback: (Rect bounds) {
return LinearGradient(
begin: Alignment.topCenter,
end: Alignment.bottomCenter,
colors: [Colors.red,Colors.blue,Colors.green],
).createShader(bounds);
},
blendMode: BlendMode.color,
child: Image.asset(
'assets/images/b.jpg',
fit: BoxFit.cover,
),
)
begin 和 end 表示渐变的方向，上面设置的方向是从顶部中间到底部中间。
color 表示渐变的颜色。
设置各个渐变色的结束点：
Color color = Colors.orange;
return ShaderMask(
shaderCallback: (Rect bounds) {
return LinearGradient(
begin: Alignment.topCenter,
end: Alignment.bottomCenter,
colors: [color,color,Colors.transparent,Colors.transparent,color,color],
stops: [0,.4,.41,.6,.61,1]
).createShader(bounds);
},
blendMode: BlendMode.color,
child: Image.asset(
'assets/images/b.jpg',
fit: BoxFit.cover,
),
);
stops 的个数要对应 color 。
由于中间设置的渐变色为透明，所以中间是原图。
RadialGradient
RadialGradient 是放射状渐变。
ShaderMask(
shaderCallback: (Rect bounds) {
return RadialGradient(
radius: .5,
colors: <Color>[Colors.red, Colors.blue],
).createShader(bounds);
},
blendMode: BlendMode.color,
child: Image.asset(
'assets/images/b.jpg',
fit: BoxFit.cover,
),
)
实现中间显示圆形原图，其他地方有灰色蒙板：
ShaderMask(
shaderCallback: (Rect bounds) {
return RadialGradient(
radius: .6,
colors: <Color>[
Colors.transparent,
Colors.transparent,
Colors.grey.withOpacity(.7),
Colors.grey.withOpacity(.7)
],
stops: [0, .5, .5, 1],
).createShader(bounds);
},
blendMode: BlendMode.srcATop,
child: Image.asset(
'assets/images/b.jpg',
fit: BoxFit.cover,
),
)
SweepGradient
SweepGradient 扇形渐变效果。
ShaderMask(
shaderCallback: (Rect bounds) {
return SweepGradient(
colors: <Color>[
Colors.red,
Colors.blue
],
).createShader(bounds);
},
child: Image.asset(
'assets/images/b.jpg',
fit: BoxFit.cover,
),
)
startAngle 和 endAngle 表示开始和结束角度。
绘制渐变圆环：
Container(
width: 200,
height: 200,
child: CustomPaint(
painter: _CircleProgressPaint(.5),
),
)
class _CircleProgressPaint extends CustomPainter {
final double progress;
_CircleProgressPaint(this.progress);
Paint _paint = Paint()
..style = PaintingStyle.stroke
..strokeWidth = 20;
@override
void paint(Canvas canvas, Size size) {
_paint.shader = ui.Gradient.sweep(
Offset(size.width / 2, size.height / 2), [Colors.red, Colors.yellow]);
canvas.drawArc(
Rect.fromLTWH(0, 0, size.width, size.height), 0, pi*2, false, _paint);
}
@override
bool shouldRepaint(CustomPainter oldDelegate) {
return true;
}
}
除了图片，可以给任何组件加入渐变效果，比如文字：
ShaderMask(
shaderCallback: (Rect bounds) {
return LinearGradient(
colors: <Color>[Colors.blue, Colors.red],
tileMode: TileMode.mirror,
).createShader(bounds);
},
blendMode: BlendMode.srcATop,
child: Center(
child: Text(
'老孟，一枚有态度的程序员',
style: TextStyle(fontSize: 24),
),
),
)
