我正在尝试在应该关注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,因为它们具有不同的偏移,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this example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)。我怀疑我不会考虑将枢轴点的新偏移量考虑到translateX
和translateY
,但我无法确定应该在何处以及如何执行此操作。
任何帮助将不胜感激。
答案 0 :(得分:10)
好的,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&amp; 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,所有这一切都很容易,但当它不是时会发生什么?
好吧,让我们看看另一个案例 - 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}。
概括来说,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 - 然后我们扩展X&amp; 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(我只会演示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。
希望这会有所帮助。