手指繪圖（貝塞爾曲線）

貝塞爾曲線是應用於二維圖形應用程序的數學曲線。

曲線的定義有四個點：起始點、終止點（也稱錨點）以及兩個相互分離的中間點。

滑動兩個中間點，貝塞爾曲線的形狀會發生變化

</pre><p></p><pre name="code" class="java">import android.app.Activity; import android.os.Bundle; import android.content.Context; import android.graphics.*; import android.view.MotionEvent; import android.view.View; public class TouchScreenActivity extends Activity { private Paint mPaint; @Override protected void onCreate(Bundle savedInstanceState) { super.onCreate(savedInstanceState); setContentView(new TouchView(this)); mPaint = new Paint(); mPaint.setAntiAlias(true); <span style="color: rgb(0, 130, 0); font-family: Consolas, 'Courier New', Courier, mono, serif; line-height: 18px; ">//設置抗鋸齒，讓繪畫比較平滑 </span> mPaint.setDither(true); <span style="color: rgb(0, 130, 0); font-family: Consolas, 'Courier New', Courier, mono, serif; line-height: 18px; ">//設置遞色</span> mPaint.setColor(0xFF00FF00); mPaint.setStyle(Paint.Style.STROKE); mPaint.setStrokeJoin(Paint.Join.ROUND); mPaint.setStrokeCap(Paint.Cap.ROUND); mPaint.setStrokeWidth(10); } public class TouchView extends View { private Bitmap mBitmap; private Canvas mCanvas; private Path mPath; private Paint mBitmapPaint; public TouchView(Context c) { super(c); /* android.graphics.Bitmap.Config是一個枚舉類型,里面定義了位圖的四種格式 * ALPHA_8:數字為8，圖形參數應該由一個字節來表示,應該是一種8位的位圖 ARGB_4444:4+4+4+4=16，圖形的參數應該由兩個字節來表示,應該是一種16位的位圖. ARGB_8888:8+8+8+8=32，圖形的參數應該由四個字節來表示,應該是一種32位的位圖. RGB_565:5+6+5=16，圖形的參數應該由兩個字節來表示,應該是一種16位的位圖. 網上講,ALPHA_8，ARGB_4444,ARGB_8888都是透明的位圖,也就是所字母A代表透明. ARGB_4444:意味着有四個參數,即A,R,G,B,每一個參數由4bit表示. 同理: ARGB_8888:意味着有四個參數,即A,R,G,B,每一個參數由8bit來表示. 同理: RGB_565:意味着有三個參數,R,G,B,三個參數分別占5bit,6bit,5bit. */ mBitmap = Bitmap.createBitmap(480, 800, Bitmap.Config.RGB_565); mCanvas = new Canvas(mBitmap); mPath = new Path(); mBitmapPaint = new Paint(Paint.DITHER_FLAG); } @Override protected void onDraw(Canvas canvas) { canvas.drawBitmap(mBitmap, 0, 0, mBitmapPaint); canvas.drawPath(mPath, mPaint); } private float mX, mY; //只有當移動的距離大於4px時,才在屏幕上繪圖 private static final float TOUCH_TOLERANCE = 4; private void touch_start(float x, float y) { mPath.reset(); mPath.moveTo(x, y); mX = x; mY = y; } private void touch_move(float x, float y) { float dx = Math.abs(x - mX); float dy = Math.abs(y - mY); if (dx >= TOUCH_TOLERANCE || dy >= TOUCH_TOLERANCE) { mPath.quadTo(mX, mY, (x + mX)/2, (y + mY)/2);//二次方貝塞爾曲線 mX = x; mY = y; } } private void touch_up() { mPath.lineTo(mX, mY); mCanvas.drawPath(mPath, mPaint); mPath.reset(); } @Override public boolean onTouchEvent(MotionEvent event) { float x = event.getX(); float y = event.getY(); switch (event.getAction()) { case MotionEvent.ACTION_DOWN: touch_start(x, y); invalidate(); break; case MotionEvent.ACTION_MOVE: touch_move(x, y); invalidate(); break; case MotionEvent.ACTION_UP: touch_up(); invalidate(); break; } return true; } } }