Android App中实现简单的刮刮卡抽奖效果的实例详解
程序员文章站
2022-05-08 12:07:03
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主要思想:
将一个view设计成多层:背景层,含中奖信息等;
遮盖层,用于刮奖,使用关联一个Bitmap的Canvas
在该Bitmap上,使用它的canvas.drawPath的api来处理 手势滑动(类似刮奖的动作)
使用paint.setXfermode 来进行消除手势滑动区域
将一个view设计成多层:背景层,含中奖信息等;
遮盖层,用于刮奖,使用关联一个Bitmap的Canvas
在该Bitmap上,使用它的canvas.drawPath的api来处理 手势滑动(类似刮奖的动作)
使用paint.setXfermode 来进行消除手势滑动区域
public class GuaView extends View { private Bitmap mBitmap; //遮盖的图层 private Canvas mCanvas; //绘制遮盖图层 private Paint mOuterPaint; private Path mPath; private float mLastX; private float mLastY; private Bitmap mCoverBitmap; //遮盖图 private int mWidth, mHeight; private Paint mInnerPaint; private String mInfo; public GuaView(Context context) { this(context, null); } public GuaView(Context context, AttributeSet attrs) { super(context, attrs); init(); } private void init() { mPath = new Path(); mOuterPaint = new Paint(); mInnerPaint = new Paint(); mCoverBitmap = BitmapFactory.decodeResource(getResources(), R.drawable.fg_guaguaka); mInfo = "¥ 5 0 0"; } @Override protected void onMeasure(int widthMeasureSpec, int heightMeasureSpec) { super.onMeasure(widthMeasureSpec, heightMeasureSpec); mWidth = mCoverBitmap.getWidth(); mHeight = mCoverBitmap.getHeight(); setMeasuredDimension(mWidth, mHeight); mBitmap = Bitmap.createBitmap(mWidth, mHeight, Bitmap.Config.ARGB_8888); mCanvas = new Canvas(mBitmap); mCanvas.drawBitmap(mCoverBitmap, 0, 0, null); setOuterPaint(); setInnerPaint(); } private void setInnerPaint() { mInnerPaint.setColor(Color.RED); mInnerPaint.setStyle(Paint.Style.STROKE); mInnerPaint.setStrokeCap(Paint.Cap.ROUND); mInnerPaint.setStrokeJoin(Paint.Join.ROUND); mInnerPaint.setAntiAlias(true); mInnerPaint.setDither(true); //防抖 mInnerPaint.setStrokeWidth(5); mInnerPaint.setTextSize(100); mInnerPaint.setTextAlign(Paint.Align.CENTER); } private void setOuterPaint() { mOuterPaint.setColor(Color.GREEN); mOuterPaint.setStyle(Paint.Style.STROKE); mOuterPaint.setStrokeCap(Paint.Cap.ROUND); mOuterPaint.setStrokeJoin(Paint.Join.ROUND); mOuterPaint.setAntiAlias(true); mOuterPaint.setDither(true); //防抖 mOuterPaint.setStrokeWidth(20); } @Override //Path public boolean onTouchEvent(MotionEvent event) { float x = event.getX(); float y = event.getY(); switch (event.getAction()) { case MotionEvent.ACTION_DOWN: mLastX = x; mLastY = y; mPath.moveTo(x, y); break; case MotionEvent.ACTION_MOVE: float deltaX = Math.abs(x - mLastX); float deltaY = Math.abs(y - mLastY); if (deltaX > 5 || deltaY > 5) { mPath.lineTo(x, y); } mLastX = x; mLastY = y; break; case MotionEvent.ACTION_UP: break; } invalidate();//调用onDraw return true; } @Override protected void onDraw(Canvas canvas) { super.onDraw(canvas); canvas.drawColor(Color.parseColor("#bbbbbb")); //背景底色 灰色 canvas.drawText(mInfo, mWidth / 2, mHeight / 4 * 3, mInnerPaint); //绘制文本 canvas.drawBitmap(mBitmap, 0, 0, null); //绘制mBitmap 这是一个可变的bitmap,通过mCanvas绘制,首先绘制了mCoverBitmap drawPath(); } private void drawPath() { //使用该mode:dst和src相交后, 只保留dst,且除去相交的部份 mOuterPaint.setXfermode(new PorterDuffXfermode(PorterDuff.Mode.DST_OUT)); mCanvas.drawPath(mPath, mOuterPaint); } }
Paint.Join 连续画笔衔接时:
MITER 在外边缘以一个锐角连接
ROUND 以圆弧
BEVEL 以直线
Paint.Cap 指定对于 线和路径(lines and paths) 的开始和结束点的处理方式:
BUTT ends with the path 不超越它
ROUND with the center at the end of the path 半圆
SQUARE with the center at the end of the path 方形
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