android - 如何在Android上绘制逆时针圆弧？

Question

如何在Android上使用canvas绘制逆时针圆弧？如果canvas不行，这里有什么解决办法吗？

Answer 1

Path.arcTo()参数SweepAngle是指旋转的角度，sweepAngle为正则圆弧顺时针旋转，sweepAngle为负则圆弧逆时针旋转。

这段代码在我的生产环境中使用，它画了一个半圆环，路径在外径顺时针，内径逆时针:

drawpercent = 0.85;

radiusPathRectF = new android.graphics.RectF((float)CentreX - (float)Radius, (float)CentreY - (float)Radius,  (float)CentreX + (float)Radius, (float)CentreY + (float)Radius);
innerradiusPathRectF = new android.graphics.RectF((float)CentreX - (float)InnerRadius, (float)CentreY - (float)InnerRadius, (float)CentreX + (float)InnerRadius, (float)CentreY + (float)InnerRadius);

Path p = new Path(); //TODO put this outside your draw() function,  you should never have a "new" keyword inside a fast loop.

                degrees = (360 + (DegreesStart)) % 360;
                radians = (360 - degrees + 90) * Math.PI / 180.0;
                //radians = Math.toRadians(DegreesStart);
                int XstartOuter = (int)Math.round((Math.cos(radians) * Radius + CentreX));
                int YstartOuter = (int)Math.round((Math.sin(-radians)* Radius + CentreY));
                int XstartInner = (int)Math.round((Math.cos(radians) * InnerRadius + CentreX));
                int YstartInner = (int)Math.round((Math.sin(-radians) * InnerRadius + CentreY));

                degrees = (360 + (DegreesStart + drawpercent * DegreesRotation)) % 360;
                //radians = degrees * Math.PI / 180.0;
                radians = (360 - degrees + 90) * Math.PI / 180.0;
                //radians = Math.toRadians(DegreesStart + drawpercent * DegreesRotation);
                int XendOuter = (int)Math.round((Math.cos(radians) * Radius + CentreX));
                int YendOuter = (int)Math.round((Math.sin(-radians) * Radius + CentreY));
                int XendInner = (int)Math.round((Math.cos(radians) * InnerRadius + CentreX));
                int YendInner = (int)Math.round((Math.sin(-radians) * InnerRadius + CentreY));

                //draw a path outlining the semi-circle ring.
                p.moveTo(XstartInner, YstartInner);
                p.lineTo(XstartOuter, YstartOuter);
                p.arcTo(radiusPathRectF, (float)DegreesStart - (float)90, (float)drawpercent * (float)DegreesRotation);
                p.lineTo(XendInner, YendInner);
                p.arcTo(innerradiusPathRectF, (float)degrees - (float)90, -1 * (float)drawpercent * (float)DegreesRotation);
                p.close();

                g.clipPath(p);

                g.drawBitmap(bitmapCircularBarImage, bitmapRect0, bitmapRectXY, paint);