Matrix原理

Matrix详解

-Matrix常用方法

setPolyToPoly
最多可以支持4个点，这4个点通常为图片的四个角，通过这四个角可将矩形变为任何形状

boolean setPolyToPoly (
        float[] src,    // 原始数组 src [x,y]，存储内容为一组点
        int srcIndex,   // 原始数组开始位置
        float[] dst,    // 目标数组 dst [x,y]，存储内容为一组点
        int dstIndex,   // 目标数组开始位置
        int pointCount) // 测控点的数量 取值范围是: 0到4

pointCount

代码：

public class PolyView extends View {
    private static final String TAG = "PolyView";
    private Bitmap bitmap;
    private Matrix matrix;
    private int pointCount = 2; //setPolyToPoly最后一个参数 作为配置项 查看效果 0 1 2 3 4
    private int triggerRadius = 100; //手指触摸半径
    private float[] src = new float[8];
    private float[] dst = new float[8];
    private Paint pointPaint = new Paint();
    public PolyView(Context context, AttributeSet attrs) {
        super(context, attrs);
        pointPaint.setAntiAlias(true);
        pointPaint.setColor(Color.GRAY);
        pointPaint.setStrokeWidth(20);
        pointPaint.setStrokeCap(Paint.Cap.ROUND);
        initBitmapAndMatrix();
    }

    private void initBitmapAndMatrix(){
        bitmap = BitmapFactory.decodeResource(getResources(), R.drawable.def);
        matrix = new Matrix();
        float[] temp = new float[]{0,0, bitmap.getWidth()+0,0, bitmap.getWidth()+0,bitmap.getHeight()+0, 0,bitmap.getHeight()+0};
        src = temp.clone();
        dst = temp.clone();
        matrix.setPolyToPoly(src,0,dst,0,pointCount);
    }

    @Override
    public boolean onTouchEvent(MotionEvent event) {
        float x = event.getX();
        float y = event.getY();
        switch (event.getAction()){
            case MotionEvent.ACTION_MOVE:
                for (int i=0; i<pointCount*2; i+=2){
                    if (Math.abs(dst[i]-x) <= triggerRadius && Math.abs(dst[i+1] - y) <= triggerRadius){
                        dst[i] = event.getX();
                        dst[i+1] = event.getY();
                        resetMatrix();
                    }
                }
                break;
        }
        return true;
    }

    private void resetMatrix(){
        matrix.reset();
        matrix.setPolyToPoly(src,0,dst,0,pointCount);
        invalidate();
    }

    @Override
    protected void onDraw(Canvas canvas) {
        super.onDraw(canvas);
        canvas.drawBitmap(bitmap,matrix,null);
        for (int i=0 ;i<pointCount*2; i+=2){
            canvas.drawPoint(dst[i],dst[i+1],pointPaint);
        }
    }
}

结果:

pointCount=0

pointCount=1

pointCount=2

pointCount=3

pointCount=4

setRectToRect

boolean setRectToRect (RectF src,           // 源区域
                RectF dst,                  // 目标区域
                Matrix.ScaleToFit stf)      // 缩放适配模式

代码：

RectF src= new RectF(0, 0, mBitmap.getWidth(), mBitmap.getHeight() );
RectF dst = new RectF(0, 0, getWidth(), getHeight());
// 核心要点
 mRectMatrix.setRectToRect(src,dst, Matrix.ScaleToFit.CENTER);
// 根据Matrix绘制一个变换后的图片
canvas.drawBitmap(mBitmap, mRectMatrix, new Paint());

Matrix.ScaleToFit.CENTER