我正在扩展一个定制的SurfaceView，并尝试使其具有缩放和滚动功能。
如何滚动：
@Override
public boolean onScroll(MotionEvent e1, MotionEvent e2,
float distanceX, float distanceY) {
// subtract scrolled amount
matrix.postTranslate(-distanceX, -distanceY);
rebound();
invalidate();
// handled
return true;
}
如何进行缩放：
@Override
public boolean onScale(ScaleGestureDetector detector) {
if (detector.isInProgress()) {
// get scale
float factor = detector.getScaleFactor();
// Don't let the object get too small or too large.
if (factor * scale > 1f) {
factor = 1f / scale;
} else if (factor * scale < minScale) {
factor = minScale / scale;
}
// store local scale
scale *= factor;
// do the scale
matrix.preScale(factor, factor, detector.getFocusX(), detector.getFocusY());
rebound();
invalidate();
}
return true;
}
onDraw中使用以下代码：）
@Override
protected void onDraw(Canvas canvas) {
super.onDraw(canvas);
canvas.save();
canvas.setMatrix(matrix);
// [...] stuff drawn with matrix settings
canvas.restore();
// [...] stuff drawn without matrix settings, as an overlay
}
目前这两种方法都运行良好。缩放在最小值（在0f和1f之间）和最大值（当前始终为1f）的比例值上正确停止。
使用的全局字段：
drawW，drawH=float，表示缩放为1时画布数据的像素大小。parentW，parentH=float，表示可见视图的像素大小。matrix=android.graphics.Matrix。
问题在于我正在尝试实现的“rebound()”方法（也许需要一个更好的名称，呵呵），它会自动强制内容保持在视图中。
我已经尝试了各种方法来计算边界应该在哪里（在矩形（0、0、parentW、parentH）内），并在矩阵“超出范围”时将其“转回去”。
这是我目前拥有的东西，肯定不起作用，而是将其推得更远。我觉得问题在于我的数学，而不是我的想法。请有人能否提供更简单或更清晰的代码，将矩阵转换到边缘，如果它太远和/或修复我的实现尝试的问题？用于使其出现在左上角的if检查。
public void rebound() {
// bounds
RectF currentBounds = new RectF(0, 0, drawW, drawH);
matrix.mapRect(currentBounds);
RectF parentBounds = new RectF(0, 0, parentW, parentH/2);
PointF diff = new PointF(0, 0);
if (currentBounds.left > parentBounds.left) {
diff.x += (parentBounds.left - currentBounds.left);
}
if (currentBounds.top > parentBounds.top) {
diff.y += (parentBounds.top - currentBounds.top);
}
if (currentBounds.width() > parentBounds.width()) {
if (currentBounds.right < parentBounds.right) {
diff.x += (parentBounds.right - currentBounds.right);
}
if (currentBounds.bottom < parentBounds.bottom) {
diff.y += (parentBounds.bottom - currentBounds.bottom);
}
}
matrix.postTranslate(diff.x, diff.y);
}
我之前写的一个版本在矩阵成为一个字段之前（我只是在onDraw中使用了canvas.scale()和canvas.translate()），它是可以工作的：
public void rebound() {
// bounds
int boundTop = 0;
int boundLeft = 0;
int boundRight = (int)(-scale * drawW + parentW);
int boundBottom = (int)(-scale * drawH + parentH);
if (boundLeft >= boundRight) {
mScrollX = Math.min(boundLeft, Math.max(boundRight, mScrollX));
} else {
mScrollX = 0;
}
if (boundTop >= boundBottom) {
mScrollY = Math.min(boundTop, Math.max(boundBottom, mScrollY));
} else {
mScrollY = 0;
}
}
我正在使用新的方法，以便能够在detector.getFocusX()和detector.getFocusY()为中心正确缩放。
更新：我将方法更改为现在的样子。它仍然有点问题，y方向的边界偏离中心太远，在更改缩放级别后也是错误的。我还将其设置为“preScale”和“postTranslate”，这样（据我所知）它应该始终应用比例，然后再进行平移，而不是混合它们。
最终更新：现在它可以工作了。以下是一个带注释的可行的rebound方法：
public void rebound() {
// make a rectangle representing what our current canvas looks like
RectF currentBounds = new RectF(0, 0, drawW, drawH);
matrix.mapRect(currentBounds);
// make a rectangle representing the scroll bounds
RectF areaBounds = new RectF((float) getLeft(),
(float) getTop(),
(float) parentW + (float) getLeft(),
(float) parentH + (float) getTop());
// the difference between the current rectangle and the rectangle we want
PointF diff = new PointF(0f, 0f);
// x-direction
if (currentBounds.width() > areaBounds.width()) {
// allow scrolling only if the amount of content is too wide at this scale
if (currentBounds.left > areaBounds.left) {
// stop from scrolling too far left
diff.x = (areaBounds.left - currentBounds.left);
}
if (currentBounds.right < areaBounds.right) {
// stop from scrolling too far right
diff.x = (areaBounds.right - currentBounds.right);
}
} else {
// negate any scrolling
diff.x = (areaBounds.left - currentBounds.left);
}
// y-direction
if (currentBounds.height() > areaBounds.height()) {
// allow scrolling only if the amount of content is too tall at this scale
if (currentBounds.top > areaBounds.top) {
// stop from scrolling too far above
diff.y = (areaBounds.top - currentBounds.top);
}
if (currentBounds.bottom < areaBounds.bottom) {
// stop from scrolling too far below
diff.y = (areaBounds.bottom - currentBounds.bottom);
}
} else {
// negate any scrolling
diff.y = (areaBounds.top - currentBounds.top);
}
// translate
matrix.postTranslate(diff.x, diff.y);
}