以前写as3的时候,遮罩效果一个mask属性就搞定了,真是方便。
转到android上以后,发现要实现类似的效果,可以使用Xfermode,android一共提供了三种:
AvoidXfermode;
PixelXorXfermode;
PorterDuffXfermode;
前两种已经不被推荐使用了(据说是因为不支持硬件加速,要生效得强制关闭硬件加速),就不细说了,主要说说第三种,一共提供了十六种效果(as3里也提供了类似,但是更加复杂的方法,所以对我而言还是比较熟悉的),如图所示:
但是要正确的在canvas上实现这些效果,还真是没那么容易,我也是研究了半天,终于实现了自己想要的效果,下面用一个例子说明下我的操作流程。
想要实现的效果是这样的:
简单分析一下,绘制一个圆形和一个矩形,计算好相应的坐标位置,然后使用SRC_IN进行混合就可以了,类似这样:
下面说一下我的操作流程:
1. 绘制border
2. 保存为单独层(canvas.saveLayer),特别注意这一步必须要有,否则无论如何出不来正常效果,起码我试了很久没有成功
3. 绘制填充的圆形,同时也是遮罩
4. 设置笔触的Xfermode为new PorterDuffXfermode(PorterDuff.Mode.SRC_IN)
5. 使用该笔触绘制矩形,进行混合
6. 恢复到canvas上
上代码,大家可以对照看一下各个步骤的具体代码
@Override protected void onDraw(Canvas canvas) { float strokeWidth = getResources().getDimension(R.dimen.stroke_width); int borderColor = getResources().getColor(R.color.carnation); int fillColor = getResources().getColor(R.color.carnation_lighter); int percentColor = getResources().getColor(R.color.carnation_light); int width = getWidth(); int height = getHeight(); //border Paint stroke = new Paint(Paint.ANTI_ALIAS_FLAG); stroke.setStrokeWidth(strokeWidth); stroke.setStyle(Paint.Style.STROKE); stroke.setColor(borderColor); canvas.drawOval(new RectF(strokeWidth/2,strokeWidth/2,width-strokeWidth/2,height-strokeWidth/2),stroke); //save as new layer int save = canvas.saveLayer(0,0,width,height,null,Canvas.ALL_SAVE_FLAG); //fill background Paint fill = new Paint(Paint.ANTI_ALIAS_FLAG); fill.setStyle(Paint.Style.FILL); fill.setColor(fillColor); canvas.drawOval(new RectF(strokeWidth - 1, strokeWidth - 1, width - strokeWidth + 1, height - strokeWidth + 1), fill); //mix rect fill.setColor(percentColor); fill.setXfermode(new PorterDuffXfermode(PorterDuff.Mode.SRC_IN)); canvas.drawRect(0,(1-mPercent)*height,width,height,fill); //restore to canvas canvas.restoreToCount(save); super.onDraw(canvas); }
之前也查了不少文章,貌似没有看到多少着重说saveLayer的,还是我对照官方apidemos源码试出来的,希望对遇到同样疑问的朋友有所帮助!
2015/7/9 更新:
1. 要实现混合的两个图形,必须位于同一个layer上,经测试位于不同layer上是无法混合的,即使最后都绘制到了canvas上。
2. 不同的绘制顺序,可能有不同的效果,注意一下逻辑即可。
更新一段复杂点的例子
使用了两种混合方式SRC_IN和CLEAR,主要代码如下:
1 @Override 2 protected void onDraw(Canvas canvas) { 3 int width = getWidth(); 4 int height = getHeight(); 5 6 float strokeWidth = DimenUtils.dp2px(4); 7 float pointRadius = DimenUtils.dp2px(4); 8 float gap = DimenUtils.dp2px(4); 9 float monthRadius = height * 0.2f; 10 float textSize = DimenUtils.dp2px(14); 11 12 int color = getResources().getColor(R.color.carnation); 13 int lightColor = getResources().getColor(R.color.carnation_light); 14 int lighterColor = getResources().getColor(R.color.carnation_lighter); 15 16 float degree = 360*mRate; 17 18 Paint paint = new Paint(Paint.ANTI_ALIAS_FLAG); 19 20 //new layer 21 int save = canvas.saveLayer(0, 0, width, height, null, Canvas.ALL_SAVE_FLAG); 22 23 //draw percent 24 canvas.save(); 25 float fillDistance = pointRadius+gap+strokeWidth/2; 26 canvas.translate(fillDistance,fillDistance); 27 RectF fillRect = new RectF(0,0,width-2*fillDistance,height-2*fillDistance); 28 paint.setColor(lightColor); 29 paint.setStyle(Paint.Style.FILL); 30 canvas.drawOval(fillRect,paint); 31 //mix rect 32 paint.setColor(color); 33 paint.setXfermode(new PorterDuffXfermode(PorterDuff.Mode.SRC_IN)); 34 canvas.drawRect(0, (1 - mPercent) * (height-2*fillDistance), width-2*fillDistance, height-2*fillDistance, paint); 35 canvas.restore(); 36 37 //border 38 paint.setXfermode(null); 39 paint.setStrokeWidth(strokeWidth); 40 paint.setStyle(Paint.Style.STROKE); 41 paint.setColor(lighterColor); 42 RectF borderRect = new RectF(pointRadius,pointRadius,width-pointRadius,height-pointRadius); 43 canvas.drawOval(borderRect, paint); 44 paint.setColor(color); 45 canvas.drawArc(borderRect,270,degree,false,paint); 46 //draw point 47 canvas.save(); 48 paint.setStyle(Paint.Style.FILL); 49 canvas.translate(width/2,height/2); 50 canvas.rotate(degree); 51 canvas.drawCircle(0,pointRadius-height/2,pointRadius,paint); 52 canvas.restore(); 53 54 //draw month 55 canvas.save(); 56 canvas.translate(width*0.7f,height*0.8f); 57 paint.setColor(Color.BLACK); 58 paint.setStyle(Paint.Style.STROKE); 59 paint.setStrokeWidth(gap); 60 paint.setXfermode(new PorterDuffXfermode(PorterDuff.Mode.CLEAR)); 61 canvas.drawCircle(0,0,monthRadius+gap/2,paint); 62 paint.setXfermode(null); 63 paint.setStyle(Paint.Style.FILL); 64 paint.setColor(getResources().getColor(R.color.orange)); 65 canvas.drawCircle(0,0,monthRadius,paint); 66 canvas.restoreToCount(save); 67 }