在使用轴心点进行画布缩放后,x和y坐标是错误的

Question

我正在尝试在应该关注枢轴点的画布上实现缩放.缩放工作正常,但之后用户应该能够在画布上选择元素.问题是,我的翻译值似乎不正确,因为它们有不同的偏移,而不是我不缩放到枢轴点的那些(没有枢轴点的缩放和拖动工作正常).我使用了这个例子中的一些代码.

相关代码是:

class DragView extends View {

private static float MIN_ZOOM = 0.2f;
private static float MAX_ZOOM = 2f;

// These constants specify the mode that we're in
private static int NONE = 0;
private int mode = NONE;
private static int DRAG = 1;
private static int ZOOM = 2;
public ArrayList<ProcessElement> elements;

// Visualization
private boolean checkDisplay = false;
private float displayWidth;
private float displayHeight;
// These two variables keep track of the X and Y coordinate of the finger when it first
// touches the screen
private float startX = 0f;
private float startY = 0f;
// These two variables keep track of the amount we need to translate the canvas along the X
//and the Y coordinate
// Also the offset from initial 0,0
private float translateX = 0f;
private float translateY = 0f;

private float lastGestureX = 0;
private float lastGestureY = 0;

private float scaleFactor = 1.f;
private ScaleGestureDetector detector;
...

private void sharedConstructor() {
    elements = new ArrayList<ProcessElement>();
    flowElements = new ArrayList<ProcessFlow>();
    detector = new ScaleGestureDetector(getContext(), new ScaleListener());
}

/**
 * checked once to get the measured screen height/width
 * @param hasWindowFocus
 */
@Override
public void onWindowFocusChanged(boolean hasWindowFocus) {
    super.onWindowFocusChanged(hasWindowFocus);
    if (!checkDisplay) {
        displayHeight = getMeasuredHeight();
        displayWidth = getMeasuredWidth();
        checkDisplay = true;
    }
}

@Override
public boolean onTouchEvent(MotionEvent event) {
    ProcessBaseElement lastElement = null;

    switch (event.getAction() & MotionEvent.ACTION_MASK) {
        case MotionEvent.ACTION_DOWN:
            mode = DRAG;

            // Check if an Element has been touched.
            // Need to use the absolute Position that's why we take the offset into consideration
            touchedElement = isElementTouched(((translateX * -1) + event.getX()) / scaleFactor, (translateY * -1 + event.getY()) / scaleFactor);


                //We assign the current X and Y coordinate of the finger to startX and startY minus the previously translated
                //amount for each coordinates This works even when we are translating the first time because the initial
                //values for these two variables is zero.
                startX = event.getX() - translateX;
                startY = event.getY() - translateY;
            }
            // if an element has been touched -> no need to take offset into consideration, because there's no dragging possible
            else {
                startX = event.getX();
                startY = event.getY();
            }

            break;

        case MotionEvent.ACTION_MOVE:
            if (mode != ZOOM) {
                if (touchedElement == null) {
                    translateX = event.getX() - startX;
                    translateY = event.getY() - startY;
                } else {
                    startX = event.getX();
                    startY = event.getY();
                }
            }

            if(detector.isInProgress()) {
                lastGestureX = detector.getFocusX();
                lastGestureY = detector.getFocusY();
            }

            break;

        case MotionEvent.ACTION_UP:
            mode = NONE;

            break;
        case MotionEvent.ACTION_POINTER_DOWN:
            mode = ZOOM;

            break;
        case MotionEvent.ACTION_POINTER_UP:
            break;
    }

    detector.onTouchEvent(event);
    invalidate();

    return true;
}

private ProcessBaseElement isElementTouched(float x, float y) {
    for (int i = elements.size() - 1; i >= 0; i--) {
        if (elements.get(i).isTouched(x, y))
            return elements.get(i);
    }
    return null;
}

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

    canvas.save();

    if(detector.isInProgress()) {
        canvas.scale(scaleFactor,scaleFactor,detector.getFocusX(),detector.getFocusY());
    } else
        canvas.scale(scaleFactor, scaleFactor,lastGestureX,lastGestureY);     // zoom

//        canvas.scale(scaleFactor,scaleFactor);

    //We need to divide by the scale factor here, otherwise we end up with excessive panning based on our zoom level
    //because the translation amount also gets scaled according to how much we've zoomed into the canvas.
    canvas.translate(translateX / scaleFactor, translateY / scaleFactor);

    drawContent(canvas);

    canvas.restore();
}

/**
 * scales the canvas
 */
private class ScaleListener extends ScaleGestureDetector.SimpleOnScaleGestureListener {
    @Override
    public boolean onScale(ScaleGestureDetector detector) {
        scaleFactor *= detector.getScaleFactor();
        scaleFactor = Math.max(MIN_ZOOM, Math.min(scaleFactor, MAX_ZOOM));
        return true;
    }
}
}

元素以其绝对位置保存在画布上(记住拖动).我怀疑我没有从枢轴点采取新的偏移 translateX并translateY考虑到,但我无法弄清楚我应该在哪里以及如何做到这一点.任何帮助,将不胜感激.

Answer 1

好吧,所以你基本上试图找出某个屏幕X/Y坐标对应的位置,在视图围绕某个枢轴点{Px,Py}缩放之后.

所以,让我们试着把它分解.

为了论证,我们假设Px&Py = 0,并且s = 2.这意味着视图在视图的左上角周围缩放了2倍.

在这种情况下,屏幕坐标{0,0}对应于视图中的{0,0},因为该点是唯一没有改变的点.一般来说,如果屏幕坐标等于枢轴点,则没有变化.

如果用户点击其他某个点会发生什么,让我们说{2,3}？在这种情况下,曾经{2,3}现在已经从枢轴点({0,0}}移动了2倍,因此相应的位置是{4,6}.

当枢轴点为{0,0}时,这一切都很容易,但是当它不是时会发生什么？

好吧,让我们看另一种情况 - 枢轴点现在是视图的右下角(宽度= w,高度= h - {w,h}).同样,如果用户点击相同的位置,那么相应的位置也是{w,h},但是让我们说用户点击其他位置,例如{w - 2,h - 3}？这里出现了相同的逻辑:翻译的位置是{w - 4,h - 6}.

总而言之,我们要做的是将屏幕坐标转换为平移坐标.我们需要对我们在缩放视图中的每个像素上执行的X/Y坐标执行相同的操作.

第1步 - 我们想根据支点转换X/Y位置:

X = X - Px
Y = Y - Py

第2步 - 然后我们缩放X和Y:

X = X * s
Y = Y * s

第3步 - 然后我们翻译回来:

X = X + Px
Y = Y + Py

如果我们将这个应用到我给出的最后一个例子(我将仅演示X):

Original value: X = w - 2, Px = w
Step 1: X <-- X - Px = w - 2 - w = -2
Step 2: X <-- X * s = -2 * 2 = -4
Step 3: X <-- X + Px = -4 + w = w - 4

一旦将此应用于您在缩放之前收到的任何相关的X/Y,该点将被平移以使其相对于缩放状态.

希望这可以帮助.