五角形图片

原理

        类似于圆形图片，都是将图片事在指定的模子中。

        首先计算出五角形外围五个点的坐标，通过直线连接，这样便可将五角形的区域给定住。再通过设置了BitmapShader的Paint将该路径画出即可。微信中发图片时图片会显示出一个尖角，也可以通过该种思路完成。

代码

public class DemoView extends View {

    private Paint paint;
    private Bitmap bitmap;

    public DemoView(Context context) {
        this(context, null);
    }

    public DemoView(Context context, AttributeSet attrs) {
        this(context, attrs, 0);
    }

    public DemoView(Context context, AttributeSet attrs, int defStyleAttr) {
        super(context, attrs, defStyleAttr);
        init();
    }

    private void init() {
        paint = new Paint();
        bitmap = BitmapFactory.decodeResource(getResources(), R.mipmap.fengjing);
        setLayerType(LAYER_TYPE_SOFTWARE, null);
    }

    @Override
    protected void onMeasure(int widthMeasureSpec, int heightMeasureSpec) {//将可能非正方形变成正方形
        int widthSize = MeasureSpec.getSize(widthMeasureSpec);
        switch (MeasureSpec.getMode(widthMeasureSpec)){
            case MeasureSpec.AT_MOST:
                widthSize = Math.min(widthSize,bitmap.getWidth());
                break;
            case MeasureSpec.UNSPECIFIED:
                widthSize = bitmap.getWidth();
                break;
        }
        int heightSize = MeasureSpec.getSize(heightMeasureSpec);
        switch (MeasureSpec.getMode(heightMeasureSpec)){
            case MeasureSpec.AT_MOST:
                heightSize = Math.min(heightSize,bitmap.getHeight());
                break;
            case MeasureSpec.UNSPECIFIED:
                heightSize = bitmap.getHeight();
                break;
        }
        int size = Math.min(widthSize, heightSize);
        setMeasuredDimension(MeasureSpec.makeMeasureSpec(size, MeasureSpec.EXACTLY), MeasureSpec.makeMeasureSpec(size, MeasureSpec.EXACTLY));
    }

    @Override
    protected void onDraw(Canvas canvas) {
        super.onDraw(canvas);
        paint.setTextSize(100);
        BitmapShader shader = new BitmapShader(bitmap, Shader.TileMode.CLAMP, Shader.TileMode.CLAMP);
        Matrix matrix = new Matrix();
        matrix.preScale(getWidth() * 1.0f / bitmap.getWidth(), getHeight() * 1.0f / bitmap.getHeight());
        paint.setAntiAlias(true);
//        matrix.preTranslate(bitmap.getWidth() /2,bitmap.getHeight() /2);
        shader.setLocalMatrix(matrix);
        paint.setShader(shader);
        paint.setStyle(Paint.Style.FILL);
        Path path = new Path();
        PointF topPoint = getTopPoint();
        path.moveTo(topPoint.x, topPoint.y);
        PointF lb = getLB();
        path.lineTo(lb.x,lb.y);
        PointF rt = getRT();
        path.lineTo(rt.x,rt.y);
        PointF lt = getLT();
        path.lineTo(lt.x,lt.y);
        PointF rb = getRB();
        path.lineTo(rb.x,rb.y);
        path.close();
        canvas.drawPath(path,paint);
    }

    private float getLength() {//计算五角形边的长度
        return (float) (getWidth() * sin(36));
    }

    private PointF getTopPoint() {
        PointF pointF = new PointF();
        pointF.set(getWidth() / 2, 0);
        return pointF;
    }

    //left-top
    private PointF getLT() {
        PointF pointF = new PointF();
        pointF.set((getWidth() - getWidth() * (float) sin(72)) / 2, getWidth() * (float) sin(36) * (float) sin(36));
        return pointF;
    }

    //right-top
    private PointF getRT() {
        PointF pointF = new PointF();
        pointF.set((getWidth() + getWidth() * (float) sin(72)) / 2, getWidth() * (float) sin(36) * (float) sin(36));
        return pointF;
    }
    //right-bottom
    private PointF getRB() {
        PointF lt = getRT();
        PointF pointF = new PointF();
        pointF.set(lt.x - getLength() * (float)sin(18),lt.y + getLength() * (float)cos(18));
        return pointF;
    }
    //left-bottom
    private PointF getLB() {
        PointF lt = getLT();
        PointF pointF = new PointF();
        pointF.set(lt.x+getLength() * (float)sin(18),lt.y + getLength() * (float)cos(18));
        return pointF;
    }

    private double sin(double angle) {
        return Math.sin(Math.toRadians(angle));
    }

    private double cos(double angle) {
        return Math.cos(Math.toRadians(angle));
    }
}

注释

        主要是通过BitmapShader完成的绘制。任何形状的图形，只要先勾勒出区域，然后按BitmapShader方式进行绘制，都可以绘制到指定的形状。