用自定义view实现刮刮乐

今天闲来无事，想实现一个刮刮乐

开始觉得很简单，做的时候发现好乱，做完回头看看发现又是好简单。。。

实现思路：利用view的ondraw方法， 不断重新绘制bitmap(我们刮刮乐的涂层图片)，然后在重写onTouchEvent的方法里面对bitmap(刮刮乐涂层图片)进行局部透明度处理。

不多说，直接贴代码，实现效果很简单，如果有不了解的地方可以评论或者870135993私聊我

public class CanvasView extends View {
    private Paint paint;
    int width;
    int height;
    int y = 0;
    int x = 0;
    Bitmap bitmap;//要被改动的图
    int marginTop = 300;//图片与屏幕顶部距离
    int widthScale = 1;//图宽的缩放比
    int heightScale = 3;//图高的缩放比

    int size = 10;//长方条的长宽,用于画长方条
    int r = 30;//画圆的半径,用于画圆

    public CanvasView(Context context) {
        super(context, null);
    }


    public CanvasView(Context context, AttributeSet attrs) {
        super(context, attrs, 0);
        paint = new Paint();
        height = ((Activity) context).getWindowManager().getDefaultDisplay().getHeight();
        width = ((Activity) context).getWindowManager().getDefaultDisplay().getWidth();
        bitmap = BitmapFactory.decodeResource(context.getResources(),
                R.mipmap.gray_back);
        float scaleWidth = ((float) width / widthScale) / bitmap.getWidth();
        float scaleHeight = ((float) height / heightScale) / bitmap.getHeight();
        Matrix matrix = new Matrix();
        matrix.postScale(scaleWidth, scaleHeight);
        bitmap = Bitmap.createBitmap(bitmap, 0, 0, bitmap.getWidth(), bitmap.getHeight(), matrix, true);
    }


    @Override
    protected void onDraw(Canvas canvas) {
        super.onDraw(canvas);
        canvas.drawBitmap(bitmap, 0, marginTop, paint);
    }

    @Override
    public boolean onTouchEvent(MotionEvent event) {
        switch (event.getAction()) {
            case MotionEvent.ACTION_DOWN:
                y = (int) event.getY();
                x = (int) event.getX();
                break;
            case MotionEvent.ACTION_MOVE:
                y = (int) event.getY();
                x = (int) event.getX();
                break;
            default:
                break;
        }

//        drawRect();//画长条
        drawCircle();//画圆
        return true;
    }

    //画长方条
    private void drawRect() {
        if (x >= size && x < (bitmap.getWidth() - size) && (y >= (marginTop + size)) && y < (bitmap.getHeight() + (marginTop - size))) {
            bitmap = bitmap.copy(Bitmap.Config.ARGB_8888, true);
            //画一长方条
            for (int i = -size; i < size; i++) {
                for (int j = -size; j < size; j++) {
                    bitmap.setPixel(x + i, y - marginTop + j, Color.TRANSPARENT);  //替换成透明色
                }
            }
            invalidate();
        }
    }

    //画圆
    private void drawCircle() {
        if (x >= 0 && x < bitmap.getWidth() && y >= marginTop && y < bitmap.getHeight() + marginTop) {
            bitmap = bitmap.copy(Bitmap.Config.ARGB_8888, true);
            for (int i = 0; i < 360; i++) {
                double rad = i * Math.PI / 180; //计算弧度
                int y1 = (int) (r * Math.sin(rad) + y) - marginTop;
                int x1 = (int) (r * Math.cos(rad) + x);
                int length = y1 - (y - marginTop);
                for (int j = 0; j < Math.abs(length); j++) {
                    if (length >= 0) {
                        if (x1 >= 0 && x1 < bitmap.getWidth() && (y1 - j) >= 0 && (y1 - j) < bitmap.getHeight()) {
                            bitmap.setPixel(x1, y1 - j, Color.TRANSPARENT);  //上半圆替换成透明色
                        }
                    } else {
                        if (x1 >= 0 && x1 < bitmap.getWidth() && (y1 + j) >= 0 && (y1 + j) < bitmap.getHeight()) {
                            bitmap.setPixel(x1, y1 + j, Color.TRANSPARENT);  //下半圆替换成透明色
                        }
                    }
                }
            }
            for (int i = x - r; i < x + r; i++) {
                if (i >= 0 && i < bitmap.getWidth()) {
                    bitmap.setPixel(i, y - marginTop, Color.TRANSPARENT);  //圆中间那条线变透明
                }
            }
        }
        invalidate();
    }

}