Android Canvas绘制正多边形和正多角星

墨蓝 2022-07-15 16:15 221阅读 0赞

顶点数在<5时没有正多角星，顶点数>5时正多角星不唯一，本文只绘制最具代表性的一种

代码如下：

public class CanvasStar extends View{
    
        public CanvasStar(Context context) {
            super(context);
        }
    
        public CanvasStar(Context context, AttributeSet attrs) {
            super(context, attrs);
        }
    
        public CanvasStar(Context context, AttributeSet attrs, int defStyleAttr) {
            super(context, attrs, defStyleAttr);
        }
    
        public CanvasStar(Context context, AttributeSet attrs, int defStyleAttr, int defStyleRes) {
            super(context, attrs, defStyleAttr, defStyleRes);
        }
    
        @Override
        protected void onDraw(Canvas canvas) {
            super.onDraw(canvas);
    
            Paint paint=new Paint();
            paint.setAntiAlias(true);
    
            drawStar(canvas,paint,Color.RED,getHeight()/12,3,false);
            canvas.translate(getHeight()/6,0);
            drawStar(canvas,paint,Color.RED,getHeight()/12,3,true);
            canvas.translate(-getHeight()/6,0);
            canvas.translate(0,getHeight()/6);
            drawStar(canvas,paint,Color.YELLOW,getHeight()/12,4,false);
            canvas.translate(getHeight()/6,0);
            drawStar(canvas,paint,Color.YELLOW,getHeight()/12,4,true);
            canvas.translate(-getHeight()/6,0);
            canvas.translate(0,getHeight()/6);
            drawStar(canvas,paint,Color.GREEN,getHeight()/12,5,false);
            canvas.translate(getHeight()/6,0);
            drawStar(canvas,paint,Color.GREEN,getHeight()/12,5,true);
            canvas.translate(-getHeight()/6,0);
            canvas.translate(0,getHeight()/6);
            drawStar(canvas,paint,Color.CYAN,getHeight()/12,6,false);
            canvas.translate(getHeight()/6,0);
            drawStar(canvas,paint,Color.CYAN,getHeight()/12,6,true);
            canvas.translate(-getHeight()/6,0);
            canvas.translate(0,getHeight()/6);
            drawStar(canvas,paint,Color.BLUE,getHeight()/12,7,false);
            canvas.translate(getHeight()/6,0);
            drawStar(canvas,paint,Color.BLUE,getHeight()/12,7,true);
            canvas.translate(-getHeight()/6,0);
            canvas.translate(0,getHeight()/6);
            drawStar(canvas,paint,Color.BLACK,getHeight()/12,8,false);
            canvas.translate(getHeight()/6,0);
            drawStar(canvas,paint,Color.BLACK,getHeight()/12,8,true);
            canvas.translate(0,getHeight()/6);
    
        }
    
        /**
         * 绘制彩色多边形或星形
         * @param canvas Canvas画布
         * @param paint Paint画笔
         * @param color 颜色
         * @param radius 外接圆半径
         * @param count 外顶点数
         * @param isStar 是否为星形
         */
        private void drawStar(Canvas canvas, Paint paint, @ColorInt int color, float radius,int count,boolean isStar){
            canvas.translate(radius,radius);
            if ((!isStar) && count < 3){
                canvas.translate(-radius,-radius);
                return;
            }
            if (isStar && count < 5){
                canvas.translate(-radius,-radius);
                return;
            }
            canvas.rotate(-90);
            if (paint == null){
                paint = new Paint();
            }else{
                paint.reset();
            }
            Path path = new Path();
            float inerRadius = count%2==0?
                    (radius*(cos(360/count/2)-sin(360/count/2)*sin(90-360/count)/cos(90-360/count)))
                    :(radius*sin(360/count/4)/sin(180-360/count/2-360/count/4));
            for (int i=0;i<count;i++){
                if (i==0){
                    path.moveTo(radius*cos(360/count*i),radius*sin(360/count*i));
                }else{
                    path.lineTo(radius*cos(360/count*i),radius*sin(360/count*i));
                }
                if (isStar){
                    path.lineTo(inerRadius*cos(360/count*i+360/count/2),inerRadius*sin(360/count*i+360/count/2));
                }
            }
            path.close();
            paint.setColor(color);
            canvas.drawPath(path,paint);
            canvas.rotate(90);
            canvas.translate(-radius,-radius);
        }
        
        /**
         * Math.sin的参数为弧度，使用起来不方便，重新封装一个根据角度求sin的方法
         * @param num 角度
         * @return
         */
        float sin(int num){
            return (float) Math.sin(num*Math.PI/180);
        }
    
        /**
         * 与sin同理
         */
        float cos(int num){
            return (float) Math.cos(num*Math.PI/180);
        }
    }

效果如下：

![20161021165518094][]

[20161021165518094]: /images/20220715/26ea780ab5644f4da4459029522e8701.png