Josh McFarland

package your.class.here;
 
import android.content.Context;
import android.graphics.Bitmap;
import android.graphics.Canvas;
import android.graphics.Color;
import android.graphics.Paint;
import android.graphics.Paint.Cap;
import android.graphics.Paint.Join;
import android.graphics.Paint.Style;
import android.graphics.Path;
import android.graphics.PorterDuff.Mode;
import android.util.AttributeSet;
import android.view.MotionEvent;
import android.view.View;
 
public class CanvasView extends View {
	private Bitmap mBitmap;
	private Canvas mCanvas;
	private Paint mPaint, mBitmapPaint;
	private Path mPath;
 
	// contructors
	public CanvasView(Context context) {
		super(context);
		setDefaults();
	}
	public CanvasView(Context context, AttributeSet attrs) {
		super(context, attrs);
		setDefaults();
	}
	public CanvasView(Context context, AttributeSet attrs, int defStyle) {
		super(context, attrs, defStyle);
		setDefaults();
	}
 
	// sets the default canvas
	public void setDefaults() {
		mPaint = new Paint();
		mPaint.setAntiAlias(true);
		mPaint.setDither(true);
		mPaint.setColor(Color.CYAN);
		mPaint.setStyle(Paint.Style.STROKE);
	        mPaint.setStrokeJoin(Paint.Join.ROUND);
		mPaint.setStrokeCap(Paint.Cap.ROUND);
		mPaint.setStrokeWidth(12);	
		mPath = new Path();
		mBitmapPaint = new Paint(Paint.DITHER_FLAG);
	}
 
	protected void onSizeChanged(int w, int h, int oldw, int oldh) {
		super.onSizeChanged(w, h, oldw, oldh);
		mBitmap = Bitmap.createBitmap(w, h, Bitmap.Config.ARGB_8888);
		mCanvas = new Canvas(mBitmap);
	}
 
	protected void onDraw(Canvas canvas) {
		canvas.drawColor(Color.WHITE);
		canvas.drawBitmap(mBitmap, 0, 0, mBitmapPaint);
		canvas.drawPath(mPath, mPaint);
	}
 
	private float mX, mY;
    private static final float TOUCH_TOLERANCE = 5; // default 5
 
    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);
            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;
    }
 
    // clears the drawing canvas
    public void clearCanvas() {
    	mCanvas.drawColor(Color.TRANSPARENT, Mode.CLEAR);
    }
 
    // sets the drawing color
    public void setColor(int color) {
    	mPaint.setColor(color);
    }
 
    // sets the drawing style
    public void setStyle(Style style) {
    	mPaint.setStyle(style);
    }
 
    // sets the stroke join
    public void setStrokeJoin(Join join) {
    	mPaint.setStrokeJoin(join);
    }
 
    // sets the stroke cap
    public void setStrokeCap(Cap cap) {
    	mPaint.setStrokeCap(Paint.Cap.ROUND);
    }
 
    // sets the stroke width
    public void setStrokeWidth(int width) {
    	mPaint.setStrokeWidth(width);
    }
}

CanvasView canvas = (CanvasView) findViewById(R.id.canvas);
canvas.clearCanvas();
canvas.invalidate();