qt qml 刮刮卡效果

 1     Canvas {
 2         id: canvas
 3         anchors.fill: parent
 4 
 5         //
 6         property bool isFirstPaint : true;
 7         property point lastPt;
 8 
 9         //
10         onPaint: {
11             var ctx = getContext(‘2d‘);
12             if (isFirstPaint){
13                 // 首次绘制刮刮层图案
14                 ctx.fillStyle = root.maskColor;
15                 ctx.fillRect(0, 0, width, height);
16                 isFirstPaint = false;
17             }
18             else{
19                 // 去除鼠标位置的图案
20                 clearRound(ctx, lastPt, 20);
21                 lastPt = Qt.point(area.mouseX, area.mouseY);
22             }
23         }
24 
25         // 清除圆形区域
26         function clearRound(ctx, p, r)
27         {
28             ctx.save();
29             ctx.globalCompositeOperation = ‘destination-out‘;
30             ctx.beginPath();
31             ctx.arc(p.x, p.y, r, 0, 2*Math.PI, false);
32             ctx.fill();
33             ctx.restore();
34         }
35 
36         // 记录下最后的鼠标点，并请求canvas重绘
37         MouseArea {
38             id: area
39             anchors.fill: parent
40             onPressed: {canvas.lastPt = Qt.point(mouseX, mouseY);}
41             onPositionChanged: {canvas.requestPaint();}
42         }
43     }