Android Api Demos登顶之路（八十六）Graphics-->Regions

/*这个demon演示了Region的不同的组合方式。 组合即当前的Region和另外的一个Region组合，可以用不同的Op方式来进行组合。
Op是一个枚举，定义在Region类中。
假设用region1  去组合region2   
public enum Op {  
        DIFFERENCE(0), //最终区域为region1 与 region2不同的区域  
        INTERSECT(1), // 最终区域为region1 与 region2相交的区域  
        UNION(2),      //最终区域为region1 与 region2组合一起的区域  
        XOR(3),        //最终区域为region1 与 region2相交之外的区域  
        REVERSE_DIFFERENCE(4), //最终区域为region2 与 region1不同的区域  
        REPLACE(5); //最终区域为为region2的区域  
 }  
 */
public class MainActivity extends Activity {

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(new SampleView(this));
    }

    private class SampleView extends View{
        private Paint mPaint=new Paint();
        private Rect mRect1=new Rect();
        private Rect mRect2=new Rect();

        public SampleView(Context context) {
            super(context);
            setFocusable(true);

            mPaint.setAntiAlias(true);
            mPaint.setTextSize(16);
            mPaint.setTextAlign(Paint.Align.CENTER);

            mRect1.set(10, 10, 100, 80);
            mRect2.set(50, 50, 130, 110);
        }

        @Override
        protected void onDraw(Canvas canvas) {
            canvas.drawColor(Color.GRAY);

            canvas.save();
            canvas.translate(80, 5);
            //绘制原始图形
            drawOrginalRects(canvas,0xff);
            canvas.restore();

            canvas.save();
            canvas.translate(0, 120);
            //绘制组合在一起的区域
            drawRgn(canvas,Color.RED,"union",Region.Op.UNION);
            canvas.restore();

            canvas.save();
            canvas.translate(160, 120);
            //绘制组合在一起的区域
            drawRgn(canvas,Color.BLUE,"Xor",Region.Op.XOR);
            canvas.restore();

            canvas.save();
            canvas.translate(0, 260);
            //绘制组合在一起的区域
            drawRgn(canvas,Color.GREEN,"Difference",Region.Op.DIFFERENCE);
            canvas.restore();

            canvas.save();
            canvas.translate(160, 260);
            //绘制组合在一起的区域
            drawRgn(canvas,Color.WHITE,"union",Region.Op.INTERSECT);
            canvas.restore();

        }

        private void drawRgn(Canvas canvas, int color, String str, Op op) {
            if(str!=null){
                mPaint.setColor(Color.BLACK);
                canvas.drawText(str, 80, 24, mPaint);
            }

            //定义一个区域
            Region rgn=new Region();
            rgn.set(mRect1);
            rgn.op(mRect2, op);

            mPaint.setColor(color);
            //定义一个区域迭代器
            RegionIterator iter=new RegionIterator(rgn);
            Rect r=new Rect();

            canvas.translate(0, 30);
            while(iter.next(r)){
                //迭代所有的rect并绘制
                canvas.drawRect(r, mPaint);
            }
            drawOrginalRects(canvas, 0x88);
        }

        private void drawOrginalRects(Canvas canvas, int alpha) {
            mPaint.setStyle(Paint.Style.STROKE);
            mPaint.setColor(Color.RED);
            mPaint.setAlpha(alpha);
            drawCentered(canvas,mRect1,mPaint);
            mPaint.setColor(Color.BLUE);
            mPaint.setAlpha(alpha);
            drawCentered(canvas,mRect2,mPaint);
            //canvas.drawRect(mRect2, mPaint);

            mPaint.setStyle(Paint.Style.FILL);

        }

        //将外边框的宽度设置为0.5个像素
        private void drawCentered(Canvas canvas, Rect r, Paint p) {
            float inset=p.getStrokeWidth()*0.5f;
            if(inset==0){
                inset=0.5f;
            }
            canvas.drawRect(r.left+inset, r.top+inset, r.right-inset, r.bottom-inset, p);
        }
    }
}