Android Api Demos登頂之路（八十四）Graphics-->PolyToPoly

/*
 * 利用Matrix 類可以實作圖像的平衡、旋轉、綻放等。一種方法是通過指定Matrix的值來實作。
 * 另一種方法是通過Matrix的
 * setPolyToPoly(float[] src, int srcIndex, float[] dst, int dstIndex, int pointCount)
 * 方法。通過指定某點在變化前和變化後的位置，（其它點保持相對位置不變），系統自動計算實作該變化的
 * 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){
            //儲存畫布的狀态
            canvas.save();
            //設定矩陣的變換方式
            mMatrix.setPolyToPoly(src, , dst, , src.length>>);
            //在畫布上應用變換的矩陣
            canvas.concat(mMatrix);

            //繪制圖形
            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=/;
            //讓字型的中心與圖形的中心重合
            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(, );
            //移動一個點，實作平移變換,将左上頂點從0，0移到5，5其它點相對位置不變，實作按對角線方向的平移
            doDraw(canvas, new float[]{, }, new float[]{, });
            canvas.restore();

            canvas.save();
            canvas.translate(, );
            //移動兩個點，實作旋轉變換,以圓點為圓心旋轉45度
            doDraw(canvas, new float[]{,,,}, 
                    new float[]{,,,});
            canvas.restore();

            canvas.save();
            canvas.translate(, );
            //移動三個點，實作旋轉/剪切變換
            doDraw(canvas, new float[]{, , , , ,  }, 
                    new float[]{ , , , , , });
            canvas.restore();

            canvas.save();
            canvas.translate(, );
            //移動四個點，實作透視變換
            doDraw(canvas, new float[]{ , , , , , , ,  }, 
                    new float[]{  , , , , , , , });
            canvas.restore();
        }

    }

}