BufferView.java

package com.godoro.androidgraphics;

import android.content.*;
import android.graphics.*;
import android.view.*;

public class BufferView extends View {

    private Bitmap bitmap;
    private Canvas bitmapCanvas;
    private Path path;
    private Paint paint;
    private float x;
    private float y;
    private static final float TOUCH_TOLERANCE = 4;

    public BufferView(Context context) {
        super(context);
        bitmap = Bitmap.createBitmap(800, 1200, Bitmap.Config.ARGB_8888);
        bitmapCanvas = new Canvas(bitmap);
        path = new Path();
        paint = new Paint();
        paint.setAntiAlias(true);
        paint.setDither(true);
        paint.setColor(0xFF0000FF);
        paint.setStyle(Paint.Style.STROKE);
        paint.setStrokeJoin(Paint.Join.ROUND);
        paint.setStrokeCap(Paint.Cap.ROUND);
        paint.setStrokeWidth(16);
        paint.setAlpha(0xAA);

    }
    @Override
    protected void onDraw(Canvas canvas) {
        canvas.drawColor(0xFFFFFFFF);
        canvas.drawBitmap(bitmap, 0, 0, paint);
        canvas.drawPath(path, paint);
    }
    private void touchUp(float x, float y) {
        path.reset();
        path.moveTo(x, y);
        this.x = x;
        this.y = y;
    }
    private void touchMove(float x, float y) {
        float dx = Math.abs(x - this.x);
        float dy = Math.abs(y - this.y);
        if (dx >= TOUCH_TOLERANCE || dy >= TOUCH_TOLERANCE) {
            path.quadTo(this.x, this.y, (x + this.x)/2, (y + this.y)/2);
            this.x = x;
            this.y = y;
        }
    }
    private void touchUp() {
        path.lineTo(x, y);
        bitmapCanvas.drawPath(path, paint);
        path.reset();
    }
    @Override
    public boolean onTouchEvent(MotionEvent event) {
        switch (event.getAction()) {
            case MotionEvent.ACTION_DOWN:
                touchUp(event.getX(), event.getY());
                invalidate();
                break;
            case MotionEvent.ACTION_MOVE:
                touchMove(event.getX(), event.getY());
                invalidate();
                break;
            case MotionEvent.ACTION_UP:
                touchUp();
                invalidate();
                break;
        }
        return true;
    }

}