如何在android画布上绘制部分圆形矩形？

Question

我想在画布上绘制一个带有颜色（或位图）和笔触的圆角矩形填充，但没有一些选定的角，并且在某些选定的边上也没有边框。我有什么想法可以实现这一目标吗？

Answer 1

您可以将绘图过程分为两部分。

1. 绘制填充区域

   当尝试绘制标准 sdk API 不支持的形状时，Canvas.drawPath 方法将是一个很好的方法。您只需定义四个变量来表示四个角的半径。

   Path path = new Path();
   Rect drawingRect = {the rect area you want to draw}
   RectF topLeftArcBound = new RectF();
   RectF topRightArcBound = new RectF();
   RectF bottomLeftArcBound = new RectF();
   RectF bottomRightArcBound = new RectF();
   
   topRightArcBound.set(drawingRect.right - topRightRadius * 2, drawingRect.top, drawingRect.right, drawingRect.top + topRightRadius * 2);
   bottomRightArcBound.set(drawingRect.right - bottomRightRadius * 2, drawingRect.bottom - bottomRightRadius * 2, drawingRect.right, drawingRect.bottom);
   bottomLeftArcBound.set(drawingRect.left, drawingRect.bottom - bottomLeftRadius * 2, drawingRect.left + bottomLeftRadius * 2, drawingRect.bottom);
   topLeftArcBound.set(drawingRect.left, drawingRect.top, drawingRect.left + topLeftRadius * 2, drawingRect.top + topLeftRadius * 2);
   
   path.reset();
   
   path.moveTo(drawingRect.left + topLeftRadius, drawingRect.top);
   
   //draw top horizontal line
   path.lineTo(drawingRect.right - topRightRadius, drawingRect.top);
   
   //draw top-right corner
   path.arcTo(topRightArcBound, -90, 90);
   
   //draw right vertical line
   path.lineTo(drawingRect.right, drawingRect.bottom - bottomRightRadius);
   
   //draw bottom-right corner
   path.arcTo(bottomRightArcBound, 0, 90);
   
   //draw bottom horizontal line
   path.lineTo(drawingRect.left - bottomLeftRadius, drawingRect.bottom);
   
   //draw bottom-left corner
   path.arcTo(bottomLeftArcBound, 90, 90);
   
   //draw left vertical line
   path.lineTo(drawingRect.left, drawingRect.top + topLeftRadius);
   
   //draw top-left corner
   path.arcTo(topLeftArcBound, 180, 90);
   
   path.close();
   
   paint.setStyle(Paint.Style.FILL);
   canvas.drawPath(path, paint);
   

   并且您可以将选定角的半径设置为零

2. 画边框

   边框包含八个部分：

   • 左上角
   • 顶线
   • 右上角
   • 右线
   • 右下角
   • 底线
   • 左下角
   • 左线

   使用 int 值来包含选定的部分将是一个好主意

   私有静态最终 int TOP_LEFT_CORNER = 0x1;
   私有静态最终 int TOP_LINE = 0x2;
   私有静态最终 int TOP_RIGHT_CORNER = 0x4;
   私有静态最终 int RIGHT_LINE = 0x8;
   私有静态最终 int BOTTOM_RIGHT_CORNER = 0x10;
   私有静态最终 int BOTTOM_LINE = 0x20;
   私有静态最终 int BOTTOM_LEFT_CORNER = 0x40;
   私有静态最终 int LEFT_LINE = 0x80;
   
   private int selectedParts = TOP_LEFT_CORNER | TOP_LINE | TOP_RIGHT_CORNER;
   

   现在我们可以根据 selectedParts 绘制边框：

   Paint.setStyle(Paint.Style.STROKE);
   if((selectedParts & TOP_LINE) > 0){
       canvas.drawLine（drawingRect.left + topLeftRadius，drawingRect.top，drawingRect.right - topRightRadius，drawingRect.top）；
   }
   
   if((selectedParts & TOP_RIGHT_CORNER) > 0){
       canvas.drawArc(topRightArcBound, -90, 90, false,paint);
   }
   
   if((selectedParts & RIGHT_LINE) > 0){
       canvas.drawLine（drawingRect.right，drawingRect.top + topRightRadius，drawingRect.right，drawingRect.bottom - bottomRightRadius，paint）；
   }
   
   if((selectedParts & BOTTOM_RIGHT_CORNER) > 0){
       canvas.drawArc(bottomRightArcBound, 0, 90, false,paint);
   }
   
   if((selectedParts & BOTTOM_LINE) > 0){
       canvas.drawLine（drawingRect.right - bottomRightRadius，drawingRect.bottom.drawingRect.left + bottomLeftRadius，drawingRect.bottom，paint）；
   }
   
   if((selectedParts & BOTTOM_LEFT_CORNER) > 0){
       canvas.drawArc(bottomLeftArcBound, 90, 90, false,paint);
   }
   
   if((selectedParts & LEFT_LINE) > 0){
       canvas.drawLine（drawingRect.left，drawingRect.bottom - bottomLeftRadius，drawingRect.left，drawingRect.top + topLeftRadius，paint）；
   }
   
   if((selectedParts & TOP_LEFT_CORNER) > 0){
       canvas.drawArc(topLeftArcBound, 180, 90, false,paint);
   }