前言

Matrix 就是矩阵的意思，我们通常使用它进行一些图片的变化操作
平移、缩放、旋转、错切、水印等效果

矩阵

{
0,0,1
1,0,0
1,0,0
}

{
MSCALE_X MSKEW_X MTRANS_X
MSKEW_Y MSCALE_Y MTRANS_Y
MPERSP_0 MPERSP_1 MPERSP_2
}

常用api

Matrix 三种动作 pre 、post 、set

pre代表之前有操作，乖乖排队
post代表插队到第一个
set代表设置，替换之前所有

平移Translate

通过改变矩阵 MTRANS_X、MTRANS_Y

preTranslate(float dx,float dy) 
postTranslate(float dx,float dy)
setTranslate(float dx,float dy)

  private void translate() {
        mMatrix.reset();
        mMatrix.preTranslate(100, 100);
        invalidate();
    }

旋转 Rotate

通过 MSCALE_X、MSKEW_X、MSCALE_Y、MSKEW_Y

preRotate(float degrees) 
preRotate(float degrees, float dx,float dy) 
...

 private void rotate() {
        mMatrix.reset();
        mMatrix.preRotate(180, bitmap.getWidth() / 2f, bitmap.getHeight() / 2f);
        invalidate();
    }

缩放Scale

通过矩阵 MSCALE_X、MSCALE_Y

preRotate(float dx,float,dy) 
...

   private void scale() {
        mMatrix.reset();
        mMatrix.preScale(2, 2, bitmap.getWidth() / 2f, bitmap.getHeight() / 2f);
        invalidate();
    }

扭曲变幻 Skew

点(x,y)通过Skew(dx,dy,px,py)变幻之后的坐标 kx(y-py)+px , ky(x-px)+py

preSkew(float kx,float ky) 
preSkew(float kx,float ky,float px,float,py) 
...

 private void skew() {
        mMatrix.reset();
        mMatrix.preSkew(1, 0, bitmap.getWidth() / 2f, bitmap.getHeight() / 2f);
        invalidate();
    }

水印效果

   private Bitmap addStamp(Bitmap bottomBitmap) {
        Bitmap bitmap = Bitmap.createBitmap(bottomBitmap.getWidth(), bottomBitmap.getHeight(), Bitmap.Config.ARGB_8888);
        Canvas canvas = new Canvas(bitmap);
        canvas.drawBitmap(bottomBitmap, 0, 0, mPaint);
        //绘制矩形
        mPaint.setColor(Color.parseColor("#55CCCCCC"));
        RectF rectF = new RectF(0, bitmap.getHeight() - 80, bitmap.getWidth(), bitmap.getHeight());
        canvas.drawRect(rectF, mPaint);
        //绘制文字
        mPaint.setTextAlign(Paint.Align.CENTER);
        mPaint.setTextSize(20);
        mPaint.setColor(Color.parseColor("#666666"));
        canvas.drawText("多多最帅", bitmap.getWidth() / 2f, bitmap.getHeight() - 80 / 2f + 20/2f , mPaint);
        return bitmap;
    }