Android Api Demos登顶之路（八十四）Graphics-->PolyToPoly

/*
 * 利用Matrix 类可以实现图像的平衡、旋转、绽放等。一种方法是通过指定Matrix的值来实现。
 * 另一种方法是通过Matrix的
 * setPolyToPoly(float[] src, int srcIndex, float[] dst, int dstIndex, int pointCount)
 * 方法。通过指定某点在变化前和变化后的位置，（其它点保持相对位置不变），系统自动计算实现该变化的
 * Matrix.
 */
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(Paint.ANTI_ALIAS_FLAG);
        private Matrix mMatrix=new Matrix();
        private Paint.FontMetrics mFontMetrics;

        private void doDraw(Canvas canvas,float[] src,float[] dst){
            //保存画布的状态
            canvas.save();
            //设置矩阵的变换方式
            mMatrix.setPolyToPoly(src, , dst, , src.length>>);
            //在画布上应用变换的矩阵
            canvas.concat(mMatrix);

            //绘制图形
            mPaint.setColor(Color.GRAY);
            mPaint.setStyle(Paint.Style.STROKE);
            canvas.drawRect(, , , , mPaint);
            canvas.drawLine(, , , , mPaint);
            canvas.drawLine(, , , , mPaint);

            mPaint.setColor(Color.RED);
            mPaint.setStyle(Paint.Style.FILL);
            float x=/;
            //让字体的中心与图形的中心重合
            float y=/-(mFontMetrics.ascent+mFontMetrics.descent)/;
            canvas.drawText(src.length/+"", x, y, mPaint);

            canvas.restore();
        }

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

            mPaint.setStrokeWidth();
            mPaint.setTextSize();
            mPaint.setTextAlign(Paint.Align.CENTER);

            mFontMetrics=mPaint.getFontMetrics();
        }

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

            canvas.save();
            canvas.translate(, );
            //移动一个点，实现平移变换,将左上顶点从0，0移到5，5其它点相对位置不变，实现按对角线方向的平移
            doDraw(canvas, new float[]{, }, new float[]{, });
            canvas.restore();

            canvas.save();
            canvas.translate(, );
            //移动两个点，实现旋转变换,以圆点为圆心旋转45度
            doDraw(canvas, new float[]{,,,}, 
                    new float[]{,,,});
            canvas.restore();

            canvas.save();
            canvas.translate(, );
            //移动三个点，实现旋转/剪切变换
            doDraw(canvas, new float[]{, , , , ,  }, 
                    new float[]{ , , , , , });
            canvas.restore();

            canvas.save();
            canvas.translate(, );
            //移动四个点，实现透视变换
            doDraw(canvas, new float[]{ , , , , , , ,  }, 
                    new float[]{  , , , , , , , });
            canvas.restore();
        }

    }

}