Question

如何绘制一条直线（不是一条直线，只是随机连续点（就像我们用铅笔绘制的那样））然后将其删除。

Answer 1

是手指画应用

////////////******************* Pinting view *******************///////////////////
public class MyView extends View {
    int bh = originalBitmap.getHeight();
    int bw = originalBitmap.getWidth(); 

    public MyView (Context c)  {  
        super(c);
        //mBitmap = Bitmap.createBitmap(bw,bh,Bitmap.Config.ARGB_8888);
        mBitmap = Bitmap.createScaledBitmap(originalBitmap,bw,bh,true);
        mCanvas = new Canvas(mBitmap);
        mPath = new Path();
        mBitmapPaint = new Paint(Paint.DITHER_FLAG);
        mBitmapPaint.setXfermode(new PorterDuffXfermode(PorterDuff.Mode.SRC)) ;
    }
    @Override
    protected void onSizeChanged(int w, int h, int oldw, int oldh) {
        super.onSizeChanged(w, h, oldw, oldh);           
            /*mBitmap = Bitmap.createBitmap(bw, bh, Bitmap.Config.ARGB_8888);
            mCanvas = new Canvas(mBitmap);*/
    }
    @Override 
    protected void onDraw(Canvas canvas) {   
        canvas.drawColor(Color.TRANSPARENT);
        canvas.drawBitmap(mBitmap, 0, 0, mBitmapPaint);
        canvas.drawPath(mPath, mPaint);
    }
    ////////************touching evants for painting**************///////
    private float mX, mY;
    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);
            mX = x;
            mY = y;
        }
    }
    private void touch_up() {
        mPath.lineTo(mX, mY);
        // commit the path to our offscreen
        mCanvas.drawPath(mPath, mPaint);
        // kill this so we don't double draw
        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:
                //if(mode == DRAW) { mView.setOnTouchListener((OnTouchListener) this); }
                touch_move(x, y);
                invalidate();
                break;
            case MotionEvent.ACTION_UP:
                touch_up();
                invalidate();
                break;
        }
        return true;
    }  //end of touch events for image
}// end MyView

用于擦除

mPaint.setXfermode(new PorterDuffXfermode(PorterDuff.Mode.CLEAR));

Answer 2

我做的是创建了一个带有铅笔线中心点的动态数组。如果你想让铅笔如此锋利，你需要记录阵列中的所有点。并用1像素半径圆绘制所有点。半径可以改变为铅笔的清晰度。

当你需要擦除它时，当你的手指或指针穿过数组中已经输入的点时处于擦除模式时，你只需将其删除。

Answer 3

公共类MyView扩展了View {

    private static final float MINP = 0.25f;
    private static final float MAXP = 0.75f;

    private Bitmap  mBitmap;
    private Canvas  mCanvas;
    private Path    mPath;
    private Paint   mBitmapPaint;

    public MyView(Context c) {
        super(c);

        mPath = new Path();
        mBitmapPaint = new Paint(Paint.DITHER_FLAG);
    }

    @Override
    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);
    }

    @Override
    protected void onDraw(Canvas canvas) {
        canvas.drawColor(0xFFAAAAAA);

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

        canvas.drawPath(mPath, mPaint);
    }

    private float mX, mY;
    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);
            mX = x;
            mY = y;
        }
    }
    private void touch_up() {
        mPath.lineTo(mX, mY);
        // commit the path to our offscreen
        mCanvas.drawPath(mPath, mPaint);
        // kill this so we don't double draw
        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;
    }
}

Answer 4

我无法评论这个答案。擦除

mPaint.setXfermode(new PorterDuffXfermode(PorterDuff.Mode.CLEAR));

你可以通过

再次画画

mPaint.setXfermode(null);

在android中绘制和擦除行

4 个答案: