android - SweepGradient 改变开始和结束颜色的位置

Question

我想创建一个从底部 -> 左侧 -> 顶部 -> 右侧 渐变的 CircleView。
所以我像这样使用带有 SweepGradient 的 Canvas

protected void onDraw(Canvas canvas) {
    super.onDraw(canvas);
    Paint paint = new Paint();

    int[] colors = {Color.GREEN, Color.RED};
    float[] positions = {0, 1};

    SweepGradient gradient = new SweepGradient(100, 100, colors, positions);
    paint.setShader(gradient);
    canvas.drawCircle(100, 100, 100, paint);
}

但默认顺序是 right -> bottom -> left -> top 但我想要 bottom -> left -> top -> right我试过将位置更改为

float[] positions = {0.25f, 1.25f};

但它只适用于 AndroidStudio 的 Preview，当我在真实设备上运行时，它显示的结果与 positions = {0, 1} 相同

如何从 bottom -> left -> top -> right 像这样制作 SweepGradient 渐变

---更新---我们可以为 SweepGradient 使用 setLocalMatrix 像这样旋转渐变

Matrix matrix = new Matrix();
matrix.setRotate(90, 100, 100);
gradient.setLocalMatrix(matrix);

Answer 1

画圆之前旋转 Canvas 。

public class CircleView extends View {
    private Paint paint;

    public CircleView(Context context) {
        super(context);
        init();
    }

    public CircleView(Context context, AttributeSet attrs) {
        super(context, attrs);
        init();
    }

    public CircleView(Context context, AttributeSet attrs, int defStyleAttr) {
        super(context, attrs, defStyleAttr);
        init();
    }

    public void init() {
        paint = new Paint();

        int[] colors = {Color.GREEN, Color.RED};
        float[] positions = {0, 1};
        SweepGradient gradient = new SweepGradient(100, 100, colors, positions);
        paint.setShader(gradient);
    }

    @Override
    protected void onDraw(Canvas canvas) {
        super.onDraw(canvas);
        canvas.save();
        canvas.rotate(90, 100, 100);
        canvas.drawCircle(100, 100, 100, paint);
        canvas.restore();
    }
}

编辑-1:
@pkskink 建议的替代方法就是用setLocalMatrix如下所示:

public void init() {      
    int[] colors = {Color.GREEN, Color.RED};
    float[] positions = {0, 1};

    Matrix matrix = new Matrix();
    matrix.postRotate(90, 100, 100);

    Shader gradient = new SweepGradient(100, 100, colors, positions);
    gradient.setLocalMatrix(matrix);

    paint = new Paint();
    paint.setShader(gradient);
}

@Override
protected void onDraw(Canvas canvas) {
    super.onDraw(canvas);
    canvas.drawCircle(100, 100, 100, paint);
}