android 之旋转罗盘 风车 开发[通俗易懂]

public void setRotatBitmap(Bitmap bitmap) { 
rotatBitmap = bitmap; 
initSize(); 
postInvalidate(); 
} 
  
public void setRotatDrawableResource(int id) { 
  
BitmapDrawable drawable = (BitmapDrawable)getContext().getResources().getDrawable(id); 
  
setRotatDrawable(drawable); 
} 
  
public void setRotatDrawable(BitmapDrawable drawable) { 
rotatBitmap = drawable.getBitmap(); 
initSize(); 
postInvalidate(); 
}

private void initSize() { 
if (rotatBitmap == null) { 
  
// throw new NoBitMapError("Error,No bitmap in RotatView!"); 
return; 
} 
width = rotatBitmap.getWidth(); 
height = rotatBitmap.getHeight(); 
  
maxwidth = Math.sqrt(width * width + height * height); 
o_x = o_y = (float)(maxwidth / 2);//确定圆心坐标 
}

@Override
protected void onMeasure(int widthMeasureSpec, int heightMeasureSpec) { 
// TODO Auto-generated method stub 
super.onMeasure(widthMeasureSpec, heightMeasureSpec); 
// 它的宽高不是图片的宽高，而是以宽高为直角的矩形的对角线的长度 
setMeasuredDimension((int)maxwidth, (int)maxwidth); 
  
}

/** 
* 当前圆盘所转的弧度(以该 view 的中心为圆点) 
*/
float deta_degree;

@Override
protected void onDraw(Canvas canvas) { 
  
Matrix matrix = new Matrix(); 
// 设置转轴位置 
matrix.setTranslate((float)width / 2, (float)height / 2); 
  
// 开始转 
matrix.preRotate(deta_degree); 
// 转轴还原 
matrix.preTranslate(-(float)width / 2, -(float)height / 2); 
  
// 将位置送到view的中心 
matrix.postTranslate((float)(maxwidth - width) / 2, (float)(maxwidth - height) / 2); 
  
canvas.drawBitmap(rotatBitmap, matrix,paint); 
  
super.onDraw(canvas); 
}

/** 
* 通过此方法来控制旋转度数，如果超过360，让它求余，防止，该值过大造成越界 
*  
* @param added 
*/
private void addDegree(float added) { 
deta_degree += added; 
if (deta_degree > 360 || deta_degree < -360) { 
deta_degree = deta_degree % 360; 
} 
  
}

  /** 
     * 计算以(src_x,src_y)为坐标圆点，建立直角体系，求出(target_x,target_y)坐标与x轴的夹角 
     * 主要是利用反正切函数的知识求出夹角 
     *  
     * @param src_x 
     * @param src_y 
     * @param target_x 
     * @param target_y 
     * @return 
     */
    float detaDegree(float src_x, float src_y, float target_x, float target_y) { 
  
        float detaX = target_x - src_x; 
        float detaY = target_y - src_y; 
        double d; 
        //坐标在四个象限里 
        if (detaX != 0) { 
            float tan = Math.abs(detaY / detaX); 
  
            if (detaX > 0) { 
  
                //第一象限 
                if (detaY >= 0) { 
                    d = Math.atan(tan); 
  
                } else { 
                    //第四象限 
                    d = 2 * Math.PI - Math.atan(tan); 
                } 
  
            } else { 
                if (detaY >= 0) { 
                    //第二象限 
                    d = Math.PI - Math.atan(tan); 
                } else { 
                    //第三象限 
                    d = Math.PI + Math.atan(tan); 
                } 
            } 
  
        } else { 
            //坐标在y轴上 
            if (detaY > 0) { 
                //坐标在y>0上 
                d = Math.PI / 2; 
            } else { 
                //坐标在y<0上 
                d = -Math.PI / 2; 
            } 
        } 
  
        return (float)((d * 180) / Math.PI); 
    }

@Override
public boolean onTouchEvent(MotionEvent event) { 
// TODO Auto-generated method stub 
if (rotatBitmap == null) { 
  
throw new NoBitMapError("Error,No bitmap in RotatView!"); 
} 
switch (event.getAction()) { 
case MotionEvent.ACTION_DOWN: { 
down_x = event.getX(); 
down_y = event.getY(); 
current_degree = detaDegree(o_x, o_y, down_x, down_y); 
  
break; 
  
} 
case MotionEvent.ACTION_MOVE: { 
down_x = target_x = event.getX(); 
down_y = target_y = event.getY(); 
float degree = detaDegree(o_x, o_y, target_x, target_y); 
  
// 滑过的弧度增量 
float dete = degree - current_degree; 
// 如果小于-90度说明 它跨周了，需要特殊处理350->17, 
if (dete < -270) { 
dete = dete + 360; 
  
// 如果大于90度说明 它跨周了，需要特殊处理-350->-17, 
} else if (dete > 270) { 
dete = dete - 360; 
} 
  
addDegree(dete); 
current_degree = degree; 
invalidate(); 
  
break; 
}

/** 
* 最大速度 
*/
public static final double max_speed = 8; 
  
/** 
* 通过数组里所装载的数据分析出即时速度<br> 
* 原理是：计算数组里的时间长度和增量的总数，然后求出每毫秒所走过的弧度<br> 
* 当然不能超过{@link VRecord#max_speed} 
*  
* @return 
*/
public double getSpeed() { 
  
if (addCount == 0) { 
return 0; 
} 
int maxIndex = Math.min(addCount, length) - 1; 
  
if ((record[0][1] - record[maxIndex][1]) == 0) { 
return 0; 
} 
  
double detaTime = record[0][1] - record[maxIndex][1]; 
double sumdegree = 0; 
for (int i = 0; i < length - 1; i++) { 
  
sumdegree += record<I>[0]; 
// System.out.println(record[0]); 
} 
  
// System.out.println("----------"); 
// System.out.println(sumdegree); 
// System.out.println(detaTime); 
double result = sumdegree / detaTime; 
if (result > 0) { 
return Math.min(result, max_speed); 
} else { 
return Math.max(result, -max_speed); 
} 
// System.out.println("v=" + result); 
  
}