最简单基础的刮刮乐

简易效果的刮刮乐

public class XferModeView extends View {
    private Paint mPaint;
    private Bitmap dstBitmap, srcBitmap;
    private Canvas mCanvas;
    private Path mPath;

    public XferModeView(Context context, AttributeSet attrs) {
        super(context, attrs);
        initPaint();
    }

    private void initPaint() {
        mPaint = new Paint(Paint.ANTI_ALIAS_FLAG);
        mPaint.setStrokeCap(Paint.Cap.ROUND);
        mPaint.setStrokeJoin(Paint.Join.ROUND);
        mPaint.setAlpha(0);
        mPaint.setStrokeWidth(50);
        mPaint.setStyle(Paint.Style.STROKE);
        dstBitmap = decodeBitmapFormRes(getResources(), R.drawable.text, getWidth(),600);
        srcBitmap = Bitmap.createBitmap(dstBitmap.getWidth(), dstBitmap.getHeight(), Bitmap.Config.ARGB_8888);//这里不能RGB565
        mCanvas = new Canvas(srcBitmap);
        mCanvas.drawColor(Color.GRAY);
        mPath = new Path();
    }

    @Override
    protected void onDraw(Canvas canvas) {
        super.onDraw(canvas);
        canvas.drawBitmap(dstBitmap, 0, 0, null);
        drawPath();
        canvas.drawBitmap(srcBitmap, 0, 0, null);

    }

    @Override
    public boolean onTouchEvent(MotionEvent event) {
        switch (event.getAction()) {
            case MotionEvent.ACTION_DOWN:
                mPath.reset();//路径复位空白
                mPath.moveTo(event.getX(), event.getY());
                break;
            case MotionEvent.ACTION_MOVE:
                mPath.lineTo(event.getX(), event.getY());
                break;
        }
        invalidate();
        return true;
    }

    private void drawPath() {
        mPaint.setXfermode(new PorterDuffXfermode(PorterDuff.Mode.DST_IN));
        mCanvas.drawPath(mPath, mPaint);
    }

    /**
     * 测量
     */
    @Override
    protected void onMeasure(int widthMeasureSpec, int heightMeasureSpec) {
        super.onMeasure(widthMeasureSpec, heightMeasureSpec);
        int wSpecMode = MeasureSpec.getMode(widthMeasureSpec);
        int wSpecSize = MeasureSpec.getSize(widthMeasureSpec);
        int hSpecMode = MeasureSpec.getMode(heightMeasureSpec);
        int hSpecSize = MeasureSpec.getSize(heightMeasureSpec);

        if (wSpecMode == MeasureSpec.AT_MOST && hSpecMode == MeasureSpec.AT_MOST) {
            setMeasuredDimension(300, 300);
        } else if (wSpecMode == MeasureSpec.AT_MOST) {
            setMeasuredDimension(300, hSpecSize);
        } else if (hSpecMode == MeasureSpec.AT_MOST) {
            setMeasuredDimension(wSpecSize, 300);
        }
    }

    /**
     * 图片的缩放
     */
    private Bitmap decodeBitmapFormRes(Resources resources, int resId, int targetWidth, int targetHeight) {
        final BitmapFactory.Options options = new BitmapFactory.Options();
        options.inPreferredConfig = Bitmap.Config.RGB_565;
        options.inJustDecodeBounds = false;
        BitmapFactory.decodeResource(resources, resId, options);
        int inSample = calculateInSample(options, targetWidth, targetHeight);
        options.inSampleSize = inSample;
        return BitmapFactory.decodeResource(resources, resId, options);
    }

    private int calculateInSample(BitmapFactory.Options options, int targetWidth, int targetHeight) {
        if (targetWidth <= 0 || targetHeight <= 0) {
            return 1;
        }
        int inSample = 1;
        final int rawWidth = options.outWidth;
        final int rawHeight = options.outHeight;
        if (rawWidth > targetWidth || rawHeight > targetHeight) {
            final int halfWidth = rawWidth / 2;
            final int halfHeight = rawHeight / 2;
            while ((halfWidth / inSample >= targetWidth) && (halfHeight / inSample >= targetHeight)) {
                inSample *= 2;
            }
        }
        return inSample;
    }
}

待解决问题:

1. 图片大时，滑动画笔会卡
2. 图片小时，不能全屏，屏幕边缘有空白

两个问题，暂时想到解决思路：

1. 继承SurfaceView，Android SurfaceView入门学习
   2.使用Matrix.setRectToRect()方法，View的测量方法onMeasure()学习有实际案例