Eraser.java

package com.firstpeople.paintpad.painttools;

import com.firstpeople.paintpad.interfaces.ToolInterface;

import android.graphics.Canvas;
import android.graphics.Color;
import android.graphics.Paint;
import android.graphics.Path;
import android.graphics.PorterDuff;
import android.graphics.PorterDuffXfermode;

public class Eraser implements ToolInterface {
	// ֻ�е��ƶ����볬�����ֵ�Ż��ƶ�
	private static final float TOUCH_TOLERANCE = 4.0f;

	private float mCurrentX = 0.0f;
	private float mCurrentY = 0.0f;
	private Path mPath = new Path();
	private Paint mEraserPaint = new Paint();
	private boolean mHasDraw = false;
	private int eraserSize = 0;

	public Eraser(int eraserSize) {
		mEraserPaint.setStrokeWidth(eraserSize);
		this.eraserSize = eraserSize;
		setUp();
	}

	private void setUp() {
		// color�����л�Ҫ����ɫ��ģʽ������eraser
		mEraserPaint.setColor(Color.BLACK);
		mEraserPaint.setDither(true);
		mEraserPaint.setAntiAlias(true);
		mEraserPaint.setStyle(Paint.Style.STROKE);
		mEraserPaint.setStrokeJoin(Paint.Join.ROUND);
		mEraserPaint.setStrokeCap(Paint.Cap.SQUARE);
		mEraserPaint
				.setXfermode(new PorterDuffXfermode(PorterDuff.Mode.DST_OUT));
	}

	@Override
	public void draw(Canvas canvas) {
		if (null != canvas) {
			canvas.drawPath(mPath, mEraserPaint);
		}
	}

	@Override
	public void touchDown(float x, float y) {
		mPath.reset();
		mPath.moveTo(x, y);
		mCurrentX = x;
		mCurrentY = y;
	}

	@Override
	public void touchMove(float x, float y) {
		if (isMoved(x, y)) {
			drawBeziercurve(x, y);
			mCurrentX = x;
			mCurrentY = y;
			mHasDraw = true;
		}

	}

	@Override
	public void touchUp(float x, float y) {
		mPath.lineTo(x, y);
	}

	@Override
	public boolean hasDraw() {
		return mHasDraw;
	}

	// �ж��Ƿ��ƶ�
	private boolean isMoved(float x, float y) {
		float dx = Math.abs(x - mCurrentX);
		float dy = Math.abs(y - mCurrentX);
		boolean isMoved = ((dx >= TOUCH_TOLERANCE) || (dy >= TOUCH_TOLERANCE));
		return isMoved;
	}

	// ��������������
	private void drawBeziercurve(float x, float y) {
		mPath.quadTo(mCurrentX, mCurrentY, (x + mCurrentX) / 2,
				(y + mCurrentY) / 2);
	}


	@Override
	public String toString() {
		return "eraser��" + " size is"+ eraserSize;
	}
}