使用CSS3 transform scale在一个点上进行缩放。
使用CSS3 transform scale在一个点上进行缩放。
尽管下面的代码片段看起来很简短，但我花了几天的时间（真丢人！）寻找只使用CSS3的transform来实现点击缩放的方法。现在它可以工作了：\n
var current = {x: 0, y: 0, zoom: 1}, c = document.getElementById('container');
window.onclick = function(e) {
wx = current.x + e.clientX / current.zoom;
wy = current.y + e.clientY / current.zoom;
var coef = e.ctrlKey ? 0.5 : 2;
current.zoom *= coef;
current.x = wx - e.clientX / current.zoom;
current.y = wy - e.clientY / current.zoom;
c.style.transform = 'scale(' + current.zoom +') translate(' + (-current.x) + 'px,' + (-current.y) + 'px)';
};
\n
html, body { margin: 0; padding: 0; overflow: hidden; min-height: 100%; }
#container { position: absolute; transform-origin: 0 0; transition-duration: 3s;}
#item { position: absolute; left:0px; top:0px; }
\n
\n唯一的问题是过渡效果很奇怪，就好像先平移后缩放一样；它产生了奇怪的锯齿效果。如何在这种情况下实现平滑的CSS3过渡效果？\n点击这里查看奇怪过渡效果的动态GIF：http://gget.it/zf3fmwum/weirdtransition.gif\n注：被点击的点是缩放变换的固定点（例如：点击眼睛，图像会缩放，光标仍然在眼睛上），就像在Google地图中双击缩放一样。
![http://gget.it/zf3fmwum/weirdtransition.gif](\"http://gget.it/zf3fmwum/weirdtransition.gif\"){kind=link}
Zooming on a point with CSS3 transform scale是一个关于使用CSS3 transform scale进行点的缩放的问题。原因是作者想要分享自己成功校准缩放算法的经验。解决方法是通过创建一个viewer类来与底层图像进行交互。该解决方法的一个重要点是它不修改默认的transform-origin，这对于其他变换可能是有用的。
以下是问题的解决方法的代码：
var Point = (function () {
function Point(x, y) {
this.x = x;
this.y = y;
}
Point.prototype.toString = function () {
return '(' + this.x + ';' + this.y + ')';
};
return Point;
})();
var Transform = (function () {
function Transform() {
this.translate = new Point(0, 0);
this.scale = 1;
this.angle = 0;
}
return Transform;
})();
var UI;
(function (UI) {
var Viewer = (function () {
function Viewer(viewer) {
this.ticking = false;
console.info("viewer browser on: " + viewer);
this.viewer = viewer;
this.viewer.style.position = 'relative';
this.viewer.style.overflow = 'hidden';
this.viewer.style.touchAction = 'none';
this.viewer.style.backgroundColor = '#000000';
this.viewer.style['-webkit-user-select'] = 'none';
this.viewer.style['-webkit-user-drag'] = 'none';
this.viewer.style['-webkit-tap-highlight-color'] = 'rgba(0, 0, 0, 0)';
this.viewerContent = this.viewer.querySelector(".image");
if (this.viewerContent == null) {
this.viewerContent = document.createElement('img');
this.viewerContent.className = 'image';
this.viewer.appendChild(this.viewerContent);
}
this.viewerContent.style.position = 'absolute';
this.viewerContent.style.transition = 'transform 100ms linear';
console.info("image width = " + this.viewer.clientWidth + "x" + this.viewer.clientHeight);
this.transform = new Transform();
this.initializeHammerEvents();
console.info("viewer controller constructed: " + this.transform);
this.setViewPortSize({ width: this.viewer.clientWidth, height: this.viewer.clientHeight });
}
Viewer.prototype.initializeHammerEvents = function () {
var _this = this;
this.gestureManager = new Hammer.Manager(this.viewer, {
touchAction: 'pan-x pan-y'
});
this.gestureManager.add(new Hammer.Pinch({
threshold: 0
}));
this.gestureManager.on("pinchstart pinchmove", function (event) { _this.onPinch(event); });
this.viewerContent.addEventListener("click", function (event) {
_this.onImageClick(event);
});
};
Viewer.prototype.setViewPortSize = function (size) {
this.viewer.style.width = size.width + 'px';
this.viewer.style.height = size.height + 'px';
this.adjustZoom();
};
Viewer.prototype.getViewPortSize = function () {
return {
width: this.viewer.clientWidth,
height: this.viewer.clientHeight
};
};
Viewer.prototype.getDocumentSize = function () {
return {
width: this.viewerContent.clientWidth,
height: this.viewerContent.clientHeight
};
};
Viewer.prototype.setSource = function (source) {
var _this = this;
this.viewerContent.src = source;
this.viewerContent.onload = function () {
console.info("image loaded");
_this.adjustZoom();
};
};
Viewer.prototype.adjustZoom = function () {
var size = this.getViewPortSize();
var documentSize = this.getDocumentSize();
console.info("adjust zoom, documentSize: " + documentSize.width + "x" + documentSize.height);
console.info("adjust zoom, viewPortSize: " + size.width + "x" + size.height);
this.minScale = 100 / documentSize.width;
console.info("minScale=" + this.minScale);
var widthScale = size.width / documentSize.width;
var heightScale = size.height / documentSize.height;
var scale = Math.min(widthScale, heightScale);
var left = (size.width - documentSize.width) / 2;
var top = (size.height - documentSize.height) / 2;
console.log("setting content to : left => " + left + " , top => " + top, ", scale => ", scale);
this.viewerContent.style.left = left + 'px';
this.viewerContent.style.top = top + 'px';
this.transform.scale = scale;
this.updateElementTransform();
};
Viewer.prototype.onPinch = function (ev) {
var pinchCenter = new Point(ev.center.x - this.viewer.offsetLeft, ev.center.y - this.viewer.offsetTop);
console.info("pinch - center=" + pinchCenter + " scale=" + ev.scale);
if (ev.type == 'pinchstart') {
this.pinchInitialScale = this.transform.scale || 1;
}
var targetScale = this.pinchInitialScale * ev.scale;
if (targetScale <= this.minScale) {
targetScale = this.minScale;
}
if (Math.abs(this.transform.scale - this.minScale) < 1e-10
&& Math.abs(targetScale - this.minScale) < 1e-10) {
console.debug('already at min scale');
this.requestElementUpdate();
return;
}
this.zoomTo(new Point(ev.center.x, ev.center.y), targetScale);
};
Viewer.prototype.onImageClick = function (event) {
console.info("click");
var zoomCenter = new Point(event.pageX - this.viewer.offsetLeft, event.pageY - this.viewer.offsetTop);
var scaleFactor = event.shiftKey || event.ctrlKey ? 0.75 : 1.25;
this.zoomTo(zoomCenter, scaleFactor * this.transform.scale);
};
Viewer.prototype.zoomTo = function (zoomCenter, newScale) {
var viewPortSize = this.getViewPortSize();
var viewPortCenter = new Point(viewPortSize.width / 2, viewPortSize.height / 2);
var zoomRelativeCenter = new Point(zoomCenter.x - viewPortCenter.x, zoomCenter.y - viewPortCenter.y);
console.debug('clicked at ' + zoomRelativeCenter + ' (relative to center)');
var oldScale = this.transform.scale;
// calculate translate difference
// 1. center on new coordinates
var zoomDx = -(zoomRelativeCenter.x) / oldScale;
var zoomDy = -(zoomRelativeCenter.y) / oldScale;
// 2. translate from center to clicked point with new zoom
zoomDx += (zoomRelativeCenter.x) / newScale;
zoomDy += (zoomRelativeCenter.y) / newScale;
console.debug('dx=' + zoomDx + ' dy=' + zoomDy + ' oldScale=' + oldScale);
/// move to the difference
this.transform.translate.x += zoomDx;
this.transform.translate.y += zoomDy;
this.transform.scale = newScale;
console.debug("applied zoom: scale= " + this.transform.scale + ' translate=' + this.transform.translate);
this.requestElementUpdate();
};
Viewer.prototype.requestElementUpdate = function () {
var _this = this;
if (!this.ticking) {
window.requestAnimationFrame(function () { _this.updateElementTransform(); });
this.ticking = true;
}
};
Viewer.prototype.updateElementTransform = function () {
var value = [
'rotate(' + this.transform.angle + 'deg)',
'scale(' + this.transform.scale + ', ' + this.transform.scale + ')',
'translate3d(' + this.transform.translate.x + 'px, ' + this.transform.translate.y + 'px, 0px)',
];
var stringValue = value.join(" ");
console.debug("transform = " + stringValue);
this.viewerContent.style.transform = stringValue;
this.viewerContent.style.webkitTransform = stringValue;
this.viewerContent.style.MozTransform = stringValue;
this.viewerContent.style.msTransform = stringValue;
this.viewerContent.style.OTransform = stringValue;
this.ticking = false;
};
return Viewer;
})();
UI.Viewer = Viewer;
})(UI || (UI = {}));
以上是Zooming on a point with CSS3 transform scale问题的原因和解决方法的整理。
Zooming on a point with CSS3 transform scale问题的出现的原因是在应用变换时，变换的顺序会影响结果。如果在缩放（scale）和平移（translate）之间调换顺序，你会发现示例的效果会有所不同。
解决方法是保持变换的顺序，确保先进行平移再进行缩放。这样可以避免出现问题。在给出的代码示例中，作者重新实现了一个可以正常工作的版本，并在变换顺序上进行了调整。
此外，还有一个性能优化的建议，即使用translate3D代替translate，因为在许多系统上它的性能更好。
在更新的代码中，作者还考虑了附加要求，并对计算进行了修改，以包括鼠标指针偏移的差异。这样可以保持缩放后的平移围绕鼠标指针进行。
最后，还有变换顺序的重要性，并给出了一个链接，详细解释了变换顺序的影响。同时，作者也指出了代码中的一个小错误，并将其进行了修正。
通过阅读上述内容，我们可以了解到Zooming on a point with CSS3 transform scale问题的出现原因以及解决方法。