【Android零散知识】Xfermode

官网例子如下:

public class TestXfermodeView extends View {
    private final Paint paint;
    // create a bitmap with a circle, used for the "dst" image
    static Bitmap makeDst(int w, int h) {
        Bitmap bm = Bitmap.createBitmap(w, h, Bitmap.Config.ARGB_8888);
        Canvas c = new Canvas(bm);
        Paint p = new Paint(Paint.ANTI_ALIAS_FLAG);

        p.setColor(0xFFFFCC44);
        c.drawOval(new RectF(0, 0, w*3/4, h*3/4), p);
        return bm;
    }

    // create a bitmap with a rect, used for the "src" image
    static Bitmap makeSrc(int w, int h) {
        Bitmap bm = Bitmap.createBitmap(w, h, Bitmap.Config.ARGB_8888);
        Canvas c = new Canvas(bm);
        Paint p = new Paint(Paint.ANTI_ALIAS_FLAG);

        p.setColor(0xFF66AAFF);
        c.drawRect(w/3, h/3, w*19/20, h*19/20, p);
        return bm;
    }

        private static final int W = 64;
        private static final int H = 64;
        private static final int ROW_MAX = 4;   // number of samples per row

        private Bitmap mSrcB;
        private Bitmap mDstB;
        private Shader mBG;     // background checker-board pattern

        public static final Xfermode[] sModes = {
                new PorterDuffXfermode(PorterDuff.Mode.CLEAR),
                new PorterDuffXfermode(PorterDuff.Mode.SRC),
                new PorterDuffXfermode(PorterDuff.Mode.DST),
                new PorterDuffXfermode(PorterDuff.Mode.SRC_OVER),
                new PorterDuffXfermode(PorterDuff.Mode.DST_OVER),
                new PorterDuffXfermode(PorterDuff.Mode.SRC_IN),
                new PorterDuffXfermode(PorterDuff.Mode.DST_IN),
                new PorterDuffXfermode(PorterDuff.Mode.SRC_OUT),
                new PorterDuffXfermode(PorterDuff.Mode.DST_OUT),
                new PorterDuffXfermode(PorterDuff.Mode.SRC_ATOP),
                new PorterDuffXfermode(PorterDuff.Mode.DST_ATOP),
                new PorterDuffXfermode(PorterDuff.Mode.XOR),
                new PorterDuffXfermode(PorterDuff.Mode.DARKEN),
                new PorterDuffXfermode(PorterDuff.Mode.LIGHTEN),
                new PorterDuffXfermode(PorterDuff.Mode.MULTIPLY),
                new PorterDuffXfermode(PorterDuff.Mode.SCREEN)
        };

        public static final String[] sLabels = {
                "Clear", "Src", "Dst", "SrcOver",
                "DstOver", "SrcIn", "DstIn", "SrcOut",
                "DstOut", "SrcATop", "DstATop", "Xor",
                "Darken", "Lighten", "Multiply", "Screen"
        };
    PorterDuff.Mode mode = PorterDuff.Mode.CLEAR;

    public TestXfermodeView(Context context) {
        this(context, null);
    }

    public TestXfermodeView(Context context, AttributeSet attrs) {
        this(context, attrs, 0);
    }

    public TestXfermodeView(Context context, AttributeSet attrs, int defStyleAttr) {
        super(context, attrs, defStyleAttr);
        mSrcB = makeSrc(W, H);
        mDstB = makeDst(W, H);
        paint = new Paint();
        // make a ckeckerboard pattern
        Bitmap bm = Bitmap.createBitmap(new int[] { 0xFFFFFFFF, 0xFFCCCCCC,
                        0xFFCCCCCC, 0xFFFFFFFF }, 2, 2,
                Bitmap.Config.RGB_565);
        mBG = new BitmapShader(bm,
                Shader.TileMode.REPEAT,
                Shader.TileMode.REPEAT);
        Matrix m = new Matrix();
        m.setScale(6, 6);
        mBG.setLocalMatrix(m);
    }
        @Override protected void onDraw(Canvas canvas) {
            canvas.drawColor(Color.WHITE);

            Paint labelP = new Paint(Paint.ANTI_ALIAS_FLAG);
            labelP.setTextAlign(Paint.Align.CENTER);

            Paint paint = new Paint();
            paint.setFilterBitmap(false);

            canvas.translate(15, 35);

            int x = 0;
            int y = 0;
            for (int i = 0; i < sModes.length; i++) {
                // draw the border
                paint.setStyle(Paint.Style.STROKE);
                paint.setShader(null);
                canvas.drawRect(x - 0.5f, y - 0.5f,
                        x + W + 0.5f, y + H + 0.5f, paint);

                // draw the checker-board pattern
                paint.setStyle(Paint.Style.FILL);
                paint.setShader(mBG);
                canvas.drawRect(x, y, x + W, y + H, paint);

                // draw the src/dst example into our offscreen bitmap
                int sc = canvas.saveLayer(x, y, x + W, y + H, null,
                        Canvas.MATRIX_SAVE_FLAG |
                                Canvas.CLIP_SAVE_FLAG |
                                Canvas.HAS_ALPHA_LAYER_SAVE_FLAG |
                                Canvas.FULL_COLOR_LAYER_SAVE_FLAG |
                                Canvas.CLIP_TO_LAYER_SAVE_FLAG);
                canvas.translate(x, y);
                canvas.drawBitmap(mDstB, 0, 0, paint);
                paint.setXfermode(sModes[i]);
                canvas.drawBitmap(mSrcB, 0, 0, paint);
                paint.setXfermode(null);
                canvas.restoreToCount(sc);

                // draw the label
                canvas.drawText(sLabels[i],
                        x + W/2, y - labelP.getTextSize()/2, labelP);

                x += W + 10;

                // wrap around when we've drawn enough for one row
                if ((i % ROW_MAX) == ROW_MAX - 1) {
                    x = 0;
                    y += H + 30;
                }
            }
        }

}

主要核心代码如下:

                int sc = canvas.saveLayer(x, y, x + W, y + H, null,
                        Canvas.MATRIX_SAVE_FLAG |
                                Canvas.CLIP_SAVE_FLAG |
                                Canvas.HAS_ALPHA_LAYER_SAVE_FLAG |
                                Canvas.FULL_COLOR_LAYER_SAVE_FLAG |
                                Canvas.CLIP_TO_LAYER_SAVE_FLAG);
                canvas.translate(x, y);
                canvas.drawBitmap(mDstB, 0, 0, paint);
                paint.setXfermode(sModes[i]);
                canvas.drawBitmap(mSrcB, 0, 0, paint);
                paint.setXfermode(null);
                canvas.restoreToCount(sc);

1、必须是BitMap之间的重叠
2、bitmap大小一致且刚刚好重叠在一块(不重叠在一块效果如下 1-2)。


1-1
1-2 bitmap偏差

3、设置离屏缓冲,canvas.saveLayer 在两张图片重叠完后释放离屏缓冲 canvas.restoreToCount(sc);(离屏缓冲,)


拿抛物线的图,离屏缓冲

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