SweepGradient更改開始和結束顏色的位置

Question

我想創建一個CircleView，梯度從底部 - >左側 - >頂部 - >右側。
所以我用帆布SweepGradient這樣

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); 
} 

但這個默認順序是右鍵 - >下 - >左轉 - >頂但我想底部 - >左轉 - >頂 - >右鍵 我曾嘗試改變位置以

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

，但它只是在AndroidStudio的Preview的作品，當我在真實的設備上運行時，它顯示的結果一樣positions = {0, 1}

我怎樣才能讓SweepGradient梯度bottom -> left -> top -> right這樣

- - 更新--- 我們可以使用setLocalMatrix爲SweepGradient像這樣旋轉漸變

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

Answer 1

在繪製圓之前旋轉畫布。

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(); 
    } 
} 

編輯-1：
由@pkskink建議的替代方法是使用setLocalMatrix象下面這樣：

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); 
}