如何在Android上繪製逆時針圓弧？

Question

如何在Android上使用畫布繪製逆時針圓弧？ 如果畫布不能，這裏有什麼解決辦法嗎？

Answer 1

檢查該代碼，

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(); 
    } 
} 

}

Answer 2

Path.arcTo（）的參數SweepAngle指旋轉的程度，如果是sweepAngle正弧是順時針，如果sweepAngle是負電弧逆時針。

該代碼在我的生產環境中使用，它繪製半圓形環，路徑變爲順時針上的外半徑，和內半徑逆時針：

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);