android - 如何在Android上绘制逆时针弧？

Question

如何使用画布在Android上绘制逆时针弧？如果canvas不能，这里有什么解决办法吗？

Answer 1

Path.arcTo() 参数 SweepAngle 是指旋转度数，如果 sweepAngle 为正则弧为顺时针，如果 sweepAngle 为负则弧为逆时针。

这段代码在我的生产环境中使用，它画了一个半圆环，路径在外半径上顺时针，在内半径上逆时针：

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);

Answer 2

检查此代码，

    public class MainActivity extends Activity {

    @Override
    public void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);

    }

    private static class AnimView extends View {
        private Paint myPaint;
        private Paint myPaint2;
        private Paint myFramePaint;
        private RectF bigOval;
        public TextView value;
        private RectF bigOval2;
        private float myStart;
        private float mySweep;
        private float SWEEP_INC = 3;
        private float SWEEP_INC2 = 5;
        // Use this flag to control the direction of the arc's movement
        private boolean addToCircle = true;

        public AnimView(Context context) {
            super(context);
            init();
        }

        public AnimView(Context context, AttributeSet attrs) {
            super(context, attrs);
            init();
        }

        private void init() {
            myPaint = new Paint();

            myPaint.setAntiAlias(true);

            myPaint.setStyle(Paint.Style.STROKE);

            myPaint.setColor(Color.GREEN);

            myPaint.setStrokeWidth(10);

            bigOval = new RectF(40, 10, 280, 250);

            myFramePaint = new Paint();
            myFramePaint.setAntiAlias(true);
            myFramePaint.setColor(Color.WHITE);
        }

        private void drawArcs(Canvas canvas, RectF oval, boolean useCenter,
                Paint paint) {
            canvas.drawRect(oval, myFramePaint);
            canvas.drawArc(oval, myStart, mySweep, false, paint);

        }

        public void setIncrement(float newIncrement) {
            SWEEP_INC = newIncrement;

        }

        @Override
        protected void onDraw(Canvas canvas) {
            drawArcs(canvas, bigOval, true, myPaint);
            value = (TextView) findViewById(R.id.value);
            drawArcs(canvas, bigOval, true, myPaint);
            myStart = -90;
            // If the arc is currently getting bigger, decrease the value of
            // mySweep
            if (addToCircle) {
                mySweep -= SWEEP_INC;
            }
            // If the arc is currently getting smaller, increase the value of
            // mySweep
            else {
                mySweep += SWEEP_INC;
            }
            // If the animation has reached the end, reverse it

            invalidate();
        }
    }
}