安卓canvas上如何选中并清除之前画的某一笔画（橡皮功能）

Question

• 使用drawPath(Path,Paint)方法画的，所有Path存放在一个arraylist之中。
• 现在想在onTouchEvent方法中实现橡皮功能，手指触摸选中笔画并清除之。
• 有使用Paint的setStrokeWidth方法，因此画出来的笔画有粗细。

如何判断手指触点坐标是否在形成的笔画图形之内？

最核心问题在于**怎么确定笔画形成的那块区域**？

注：橡皮擦清除整条独立的笔画，类似于Google keep里的绘图那样，不是用背景色绘制触摸轨迹

下面是代码

用于储存path和画笔类型的 fingerPath类：

 import android.graphics.Path;

public class FingerPath {

    public int color;
    public boolean emboss;
    public boolean blur;
    public int strokeWidth;
    public Path path;

    public FingerPath(int color, boolean emboss, boolean blur, int strokeWidth, Path path) {
        this.color = color;
        this.emboss = emboss;
        this.blur = blur;
        this.strokeWidth = strokeWidth;
        this.path = path;
    }
}

自定义view类：

import android.content.Context;
import android.graphics.Bitmap;
import android.graphics.BlurMaskFilter;
import android.graphics.Canvas;
import android.graphics.Color;
import android.graphics.EmbossMaskFilter;
import android.graphics.MaskFilter;
import android.graphics.Paint;
import android.graphics.Path;
import android.util.AttributeSet;
import android.util.DisplayMetrics;
import android.view.MotionEvent;
import android.view.View;

import java.util.ArrayList;


public class PaintView extends View {

    public static int BRUSH_SIZE = 20;
    public static final int DEFAULT_COLOR = Color.RED;
    public static final int DEFAULT_BG_COLOR = Color.WHITE;
    private static final float TOUCH_TOLERANCE = 4;
    private float mX, mY;
    private Path mPath;
    private Paint mPaint;
    private ArrayList<FingerPath> paths = new ArrayList<>();
    private int currentColor;
    private int backgroundColor = DEFAULT_BG_COLOR;
    private int strokeWidth;
    private boolean emboss;
    private boolean blur;
    private MaskFilter mEmboss;
    private MaskFilter mBlur;
    private Bitmap mBitmap;
    private Canvas mCanvas;
    private Paint mBitmapPaint = new Paint(Paint.DITHER_FLAG);

    public PaintView(Context context) {
        this(context, null);
    }

    public PaintView(Context context, AttributeSet attrs) {
        super(context, attrs);
        mPaint = new Paint();
        mPaint.setAntiAlias(true);
        mPaint.setDither(true);
        mPaint.setColor(DEFAULT_COLOR);
        mPaint.setStyle(Paint.Style.STROKE);
        mPaint.setStrokeJoin(Paint.Join.ROUND);
        mPaint.setStrokeCap(Paint.Cap.ROUND);
        mPaint.setXfermode(null);
        mPaint.setAlpha(0xff);

        mEmboss = new EmbossMaskFilter(new float[] {1, 1, 1}, 0.4f, 6, 3.5f);
        mBlur = new BlurMaskFilter(5, BlurMaskFilter.Blur.NORMAL);
    }

    public void init(DisplayMetrics metrics) {
        int height = metrics.heightPixels;
        int width = metrics.widthPixels;

        mBitmap = Bitmap.createBitmap(width, height, Bitmap.Config.ARGB_8888);
        mCanvas = new Canvas(mBitmap);

        currentColor = DEFAULT_COLOR;
        strokeWidth = BRUSH_SIZE;
    }

    public void normal() {
        emboss = false;
        blur = false;
    }

    public void emboss() {
        emboss = true;
        blur = false;
    }

    public void blur() {
        emboss = false;
        blur = true;
    }

    public void clear() {
        backgroundColor = DEFAULT_BG_COLOR;
        paths.clear();
        normal();
        invalidate();
    }
    public void undo() {
        int size=paths.size();
        paths.remove(size-1);
        invalidate();
    }
    @Override
    protected void onDraw(Canvas canvas) {
        canvas.save();
        mCanvas.drawColor(backgroundColor);

        for (FingerPath fp : paths) {
            mPaint.setColor(fp.color);
            mPaint.setStrokeWidth(fp.strokeWidth);
            mPaint.setMaskFilter(null);

            if (fp.emboss)
                mPaint.setMaskFilter(mEmboss);
            else if (fp.blur)
                mPaint.setMaskFilter(mBlur);

            mCanvas.drawPath(fp.path, mPaint);

        }

        canvas.drawBitmap(mBitmap, 0, 0, mBitmapPaint);
        canvas.restore();
    }

    private void touchStart(float x, float y) {
        mPath = new Path();
        FingerPath fp = new FingerPath(currentColor, emboss, blur, strokeWidth, mPath);
        paths.add(fp);

        mPath.reset();
        mPath.moveTo(x, y);
        mX = x;
        mY = y;
        System.out.println("按下时list长度"+paths.size());
    }

    private void touchMove(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 touchUp() {
        mPath.lineTo(mX, mY);

    }

    @Override
    public boolean onTouchEvent(MotionEvent event) {
        float x = event.getX();
        float y = event.getY();

        switch(event.getAction()) {
            case MotionEvent.ACTION_DOWN :
                touchStart(x, y);
                invalidate();
                break;
            case MotionEvent.ACTION_MOVE :
                touchMove(x, y);
                invalidate();
                break;
            case MotionEvent.ACTION_UP :
                touchUp();
                invalidate();
                break;
        }

        return true;
    }
}

Answer 1

http://blog.csdn.net/yuanlong_zheng/article/details/7592457