如何在 android canvas 上绘制部分圆形矩形？

Question

我想在 canvas 上绘制一个 圆角矩形 填充颜色（或位图）和描边，但 没有选定的角 并且 在某些选定的边上没有边框 。有什么想法可以实现吗？

Answer 1

您可以将绘图过程分成两部分。

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 it.you 可以只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);
   

   并且您可以将所选角的半径设置为零

2. 绘制边框

   边框包含八个部分：

   • 左上角
   • 顶行
   • 右上角
   • 右行
   • 右下角
   • 底线
   • 左下角
   • 左行

   使用 int 值来包含选定的部分是个好主意

   private static final int TOP_LEFT_CORNER = 0x1;
   private static final int TOP_LINE = 0x2;
   private static final int TOP_RIGHT_CORNER = 0x4;
   private static final int RIGHT_LINE = 0x8;
   private static final int BOTTOM_RIGHT_CORNER = 0x10;
   private static final int BOTTOM_LINE = 0x20;
   private static final int BOTTOM_LEFT_CORNER = 0x40;
   private static final int LEFT_LINE = 0x80;
   
   private int selectedParts = TOP_LEFT_CORNER | TOP_LINE | TOP_RIGHT_CORNER;
   

   现在我们可以根据selectedParts绘制边框了：

   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);
   }