Question

我正在开发一个绘图应用，我想用重做/撤消选项实现橡皮擦功能。我已经浏览了CanvasView和FingerPaint个样本，但遗憾的是我无法实现橡皮擦。我使用了 paint.setXfermode（new PorterDuffXfermode（PorterDuff.Mode.CLEAR）））用于擦除但不起作用。

注意：在我的情况下橡皮擦正在工作，但重做/撤消不起作用，我希望两者都能正常工作。

我的代码：

//Here is the I am creating Paint object...

private Paint createPaint() {
    Paint paint = new Paint();
    paint.setAntiAlias(true);
    paint.setStyle(this.paintStyle);
    paint.setStrokeWidth(this.paintStrokeWidth);
    paint.setStrokeCap(this.lineCap);
    paint.setStrokeJoin(Paint.Join.MITER);  // fixed

    if (this.mode == Mode.ERASER) {
        // Eraser
        paint.setXfermode(new PorterDuffXfermode(PorterDuff.Mode.CLEAR));
        paint.setARGB(0, 0, 0, 0);

        // paint.setColor(this.baseColor);
        // paint.setShadowLayer(this.blur, 0F, 0F, this.baseColor);
    } else {
        // Otherwise
        paint.setColor(this.paintStrokeColor);
        paint.setShadowLayer(this.blur, 0F, 0F, this.paintStrokeColor);
        paint.setAlpha(this.opacity);
        paint.setPathEffect(this.drawPathEffect);
    }

    return paint;
}


//This method is for managing Redo/Undo

private void updateHistory(Path path) {
    if (this.historyPointer == this.pathLists.size()) {
        this.pathLists.add(path);
        this.paintLists.add(this.createPaint());
        this.historyPointer++;
    } else {
        // On the way of Undo or Redo
        this.pathLists.set(this.historyPointer, path);
        this.paintLists.set(this.historyPointer, this.createPaint());
        this.historyPointer++;

        for (int i = this.historyPointer, size = this.paintLists.size(); i < size; i++) {
            this.pathLists.remove(this.historyPointer);
            this.paintLists.remove(this.historyPointer);
        }
    }
}


private void onActionDown(MotionEvent event) {
    switch (this.mode) {
        case DRAW   :
        case ERASER :
                this.updateHistory(this.createPath(event));
                this.isDown = true;
        default :
            break;
    }
}

private void onActionMove(MotionEvent event) {
    float x = event.getX();
    float y = event.getY();

    switch (this.mode) {
        case DRAW   :
        case ERASER :

                Path path = this.getCurrentPath();

                switch (this.drawer) {
                    case PEN :
                        path.lineTo(x, y);
                        break;
                    default :
                        break;
                }

            break;
        default :
            break;
    }
}

private void onActionUp(MotionEvent event) {
    if (isDown) {
        this.startX = 0F;
        this.startY = 0F;
        this.isDown = false;
    }
}

@Override
protected void onDraw(Canvas canvas) {
    super.onDraw(canvas);

    // Before "drawPath"
    canvas.drawColor(this.baseColor);

    if (this.bitmap != null) {
        canvas.drawBitmap(this.bitmap, 0F, 0F, emptyPaint);
    }

    for (int i = 0; i < this.historyPointer; i++) {
        Path path   = this.pathLists.get(i);
        Paint paint = this.paintLists.get(i);

        canvas.drawPath(path, paint);
    }

    this.canvas = canvas;
}

Answer 1

 /**
 * This method draws canvas again for Undo.
 */
public boolean undo() {
    if (this.historyPointer > 1) {
        this.historyPointer--;
        this.invalidate();

        return true;
    } else {
        return false;
    }
}

/**
 * This method draws canvas again for Redo.
 */
public boolean redo() {
    if (this.historyPointer < this.pathLists.size()) {
        this.historyPointer++;
        this.invalidate();

        return true;
    } else {
        return false;
    }
}

在Android中使用重做/撤消选项的画布中的橡皮擦

1 个答案: