但本文介紹的是另外一種裁切方式，裁切框由開發者決定，圖片大小由使用者決定，通過縮放、拖動圖片來選取合適位置，並且在這一過程中始終保持圖片寬高比，如右上圖。
這樣做法主要有以下優點：
- 裁切框的寬高與跟實際使用的處寬高比一致，防止出現圖片變形問題
- 不限制圖片的顯示大小，保證圖片原始比例，通過縮放可得到原始尺寸
- 對於區域性的裁切更加友好，比如擷取一張高清圖片中很小的一個部位，我們只需將圖片放大並拖動到裁切框內即可，而其他方式需要將裁切框調整的非常小，不利於使用者操作
主體思路是利用兩張圖片，將他們絕對定位，一張放在裁切框內一張放在裁切框外並設定透明效果，裁切框overflow為hidden，時刻保持兩張圖片的絕對同步。
<div class="jimu-crop-image" data-dojo-attach-point="cropSection"> <div class="viewer-box" data-dojo-attach-point="viewerBox"> <div class="viewer-content" data-dojo-attach-point="viewerContent"> <img class="viewer-image hide-image" data-dojo-attach-point="viewerImage" src=""> </div> <img class="base-image hide-image" data-dojo-attach-point="baseImage" data-dojo-attach-event="mousedown:_onViewerMouseDown,mouseup:_onViewerMouseUp"> <div class="controller"> <div class="zoom-out" data-dojo-attach-event="click:_onZoomOutClick">-</div> <div class="slider" data-dojo-attach-point="sliderNode"> <div class="button" data-dojo-attach-point="sliderButton" data-dojo-attach-event="mousedown:_onSliderMouseDown,mouseup:_onSliderMouseUp"></div> <div class="horizontal"></div> </div> <div class="zoom-in" data-dojo-attach-event="click:_onZoomInClick">+</div> </div> </div> </div>
首先在postCreate中繫結document的mousemove跟mousedown事件，在滑鼠離開工作區後仍可以繼續拖動或縮放。接下來的主要工作在startup跟_init函式中。不熟悉dojo的道友只要知道postCreate會在startup之前執行即可。
startup: function() {
var timeOut = /data:image\/(.*);base64/.test(this.imageSrc) ? 50 : 500;
var tic = lang.hitch(this, function() {
var imageStyle = html.getComputedStyle(this.baseImage);
var imageWidth = parseFloat(imageStyle.width);
console.log('image width', imageWidth);
if (isFinite(imageWidth) && imageWidth > 0) {
this._init();
} else {
setTimeout(tic, timeOut);
}
});
setTimeout(tic, timeOut);
},
_init: function() {
debugger;
var cropSectionStyle = html.getComputedStyle(this.cropSection);
var cropSectionContentBox = html.getContentBox(this.cropSection);
var imageStyle = html.getComputedStyle(this.baseImage);
var imageWidth = parseFloat(imageStyle.width);
var imageHeight = parseFloat(imageStyle.height);
var imageRadio = imageWidth / imageHeight;
this._maxImageWidth = imageWidth;
this._maxImageHeight = imageHeight;
if (imageHeight < this.realHeight && imageWidth < this.realWidth) {
alert('image is too smaller to display');
return;
}
//create a box which keep the ratio of width and height to full fill the content of popup
this.idealWidth = this.realWidth;
this.idealHeight = this.realHeight;
this.ratio = this.ratio ? this.ratio : this.realWidth / this.realHeight;
if (this.ratio >= 1) {
if (this.realWidth <= cropSectionContentBox.w) {
this.idealWidth += (cropSectionContentBox.w - this.realWidth) / 2;
} else {
this.idealWidth = cropSectionContentBox.w;
}
this.idealHeight = this.idealWidth / this.ratio;
} else {
if (this.realHeight <= cropSectionContentBox.h) {
this.idealHeight += (cropSectionContentBox.h - this.idealHeight) / 2;
} else {
this.idealHeight = cropSectionContentBox.h;
}
this.idealWidth = this.idealHeight * this.ratio;
}
html.setStyle(this.viewerBox, {
width: this.idealWidth + 'px',
height: this.idealHeight + 'px'
});
var paddingTop = Math.abs((parseFloat(cropSectionStyle.height) - this.idealHeight) / 2);
html.setStyle(this.cropSection, {
'paddingTop': paddingTop + 'px',
'paddingBottom': paddingTop + 'px'
});
// keep original ratio of image
if (imageRadio >= 1) {
if (this.idealHeight * imageRadio >= this.idealWidth) {
html.setStyle(this.viewerImage, 'height', this.idealHeight + 'px');
html.setStyle(this.baseImage, 'height', this.idealHeight + 'px');
} else {
var properlyHeight = this._findProperlyValue(0, this.idealWidth, this.idealWidth, function(p) {
return p * imageRadio;
});
html.setStyle(this.viewerImage, 'height', properlyHeight + 'px');
html.setStyle(this.baseImage, 'height', properlyHeight + 'px');
}
} else {
if (this.idealWidth / imageRadio >= this.idealHeight) {
html.setStyle(this.viewerImage, 'width', this.idealWidth + 'px');
html.setStyle(this.baseImage, 'width', this.idealWidth + 'px');
} else {
var properlyWidth = this._findProperlyValue(0, this.idealHeight, this.idealHeight, function(p) {
return p / imageRadio;
});
html.setStyle(this.viewerImage, 'width', properlyWidth + 'px');
html.setStyle(this.baseImage, 'width', properlyWidth + 'px');
}
}
query('.hide-image', this.domNode).removeClass('hide-image');
imageStyle = html.getComputedStyle(this.baseImage);
imageWidth = parseFloat(imageStyle.width);
imageHeight = parseFloat(imageStyle.height);
this._minImageWidth = imageWidth;
this._minImageHeight = imageHeight;
this._currentImageWidth = imageWidth;
this._currentImageHeight = imageHeight;
this._currentTop = -(imageHeight - this.idealHeight) / 2;
this._currentLeft = -(imageWidth - this.idealWidth) / 2;
html.setStyle(this.baseImage, {
top: this._currentTop + 'px',
left: this._currentLeft + 'px'
});
html.setStyle(this.viewerImage, {
top: this._currentTop + 'px',
left: this._currentLeft + 'px'
});
//sometimes zoomratio < 1; it's should be not allowed to zoom
this._zoomRatio = this._maxImageWidth / this._minImageWidth;
if (!this._latestPercentage) {
this._latestPercentage = 0;
}
},這裡面做了以下幾件事：
- 等待圖片載入完畢，獲取圖片的原始尺寸，後續計算縮放因子時會用到
- 在保證裁切區域寬高比的情況下，讓裁切區域儘量的填滿工作區。這裡裁切工作最重要的就是防止圖片變形，所以只要保證寬高比一致可以將裁切區域適當放大。
- 保持圖片原始寬高比的前提下，讓圖片儘量接近裁切框
- 機上計算完成後設定圖片初始位置，讓裁切框相對圖片居中
平移的過程比較簡單，只需要記錄移動過程中滑鼠的相對位置變化，不斷改變圖片左上角的left跟top即可，在dragstart跟selectstart事件中preventDefault防止出現元素被選中變藍。
_resetImagePosition: function(clientX, clientY) {
var delX = clientX - this._currentX;
var delY = clientY - this._currentY;
if (this._currentTop + delY >= 0) {
html.setStyle(this.baseImage, 'top', 0);
html.setStyle(this.viewerImage, 'top', 0);
this._currentY = clientY;
this._currentTop = 0;
} else if (this._currentTop + delY <= this._maxOffsetTop) {
html.setStyle(this.baseImage, 'top', this._maxOffsetTop + 'px');
html.setStyle(this.viewerImage, 'top', this._maxOffsetTop + 'px');
this._currentY = clientY;
this._currentTop = this._maxOffsetTop;
} else {
html.setStyle(this.baseImage, 'top', this._currentTop + delY + 'px');
html.setStyle(this.viewerImage, 'top', this._currentTop + delY + 'px');
this._currentY = clientY;
this._currentTop += delY;
}
if (this._currentLeft + delX >= 0) {
html.setStyle(this.baseImage, 'left', 0);
html.setStyle(this.viewerImage, 'left', 0);
this._currentX = clientX;
this._currentLeft = 0;
} else if (this._currentLeft + delX <= this._maxOffsetLeft) {
html.setStyle(this.baseImage, 'left', this._maxOffsetLeft + 'px');
html.setStyle(this.viewerImage, 'left', this._maxOffsetLeft + 'px');
this._currentX = clientX;
this._currentLeft = this._maxOffsetLeft;
} else {
html.setStyle(this.baseImage, 'left', this._currentLeft + delX + 'px');
html.setStyle(this.viewerImage, 'left', this._currentLeft + delX + 'px');
this._currentX = clientX;
this._currentLeft += delX;
}
},縮放的主要原則就是保持裁剪框的中心點在縮放前後的相對位置不變。
為了將縮放後的原裁切框的中心點移回原位，我們需要計算兩中值：圖片大小變化量，圖片左上角移動量。
var delImageWidth = this._minImageWidth * (this._zoomRatio - 1) * leftPercentage / 100; var delImageHeight = this._minImageHeight * (this._zoomRatio - 1) * leftPercentage / 100; var imageStyle = html.getComputedStyle(this.baseImage); this._currentLeft = parseFloat(imageStyle.left); this._currentTop = parseFloat(imageStyle.top); var delImageLeft = (Math.abs(this._currentLeft) + this.idealWidth / 2) * ((this._minImageWidth + delImageWidth) / this._currentImageWidth - 1); var delImageTop = (Math.abs(this._currentTop) + this.idealHeight / 2) * ((this._minImageWidth + delImageWidth) / this._currentImageWidth - 1);
其中_zoomRatio = _maxImageWidth / _minImageWidth; _maxImageWidth為圖片原始大小，_minImageWidth是讓圖片接近裁切框的最小寬度。
leftPercentage為滑動按鈕相對滑動條的位移百分比。
_currentLeft、_currentTop是本次縮放前圖片相對裁切框的絕對位置(position:absolute)。
_currentImageWidth、_currentImageHeight是本次縮放前圖片的大小。
剩下要做的是防止裁切框內出現空白現象，假設使用者放大圖片，將圖片拖放到邊界與裁切框邊界重合，這時縮小圖片的話裁切框內便會出現空白。為了防止這種情況我們也需要做相應處理。
當圖片左上邊界與裁切框左上邊界重合時，無論如何縮小，image的left、top始終為零，只改變圖片大小。
當圖片右下邊界與裁切框右下邊界重合時，根據圖片大小與裁切框大小可以計算出合適的left跟top
//prevent image out the crop box
if (leftPercentage - _latestPercentage >= 0) {
console.log('zoomin');
html.setStyle(this.baseImage, {
top: this._currentTop -delImageTop + 'px',
left: this._currentLeft -delImageLeft + 'px'
});
html.setStyle(this.viewerImage, {
top: this._currentTop -delImageTop + 'px',
left: this._currentLeft -delImageLeft + 'px'
});
} else {
console.log('zoomout');
var top = 0;
var left = 0;
if (this._currentTop - delImageTop >= 0) {
top = 0;
} else if (this._currentTop - delImageTop +
this._minImageHeight + delImageHeight <=
this.idealHeight) {
top = this.idealHeight - this._minImageHeight - delImageHeight;
} else {
top = this._currentTop - delImageTop;
}
console.log(this._currentLeft, delImageLeft);
if (this._currentLeft - delImageLeft >= 0) {
left = 0;
} else if (this._currentLeft - delImageLeft +
this._minImageWidth + delImageWidth <=
this.idealWidth) {
left =this.idealWidth - this._minImageWidth - delImageWidth;
} else {
left = this._currentLeft - delImageLeft;
}
html.setStyle(this.baseImage, {
top: top + 'px',
left: left + 'px'
});
html.setStyle(this.viewerImage, {
top: top + 'px',
left: left + 'px'
});
}以上便是客戶端的實現思路。全部程式碼，瀏覽器支援：現代瀏覽器和ie9+，稍後會將ie8也支援上。
伺服器端使用nodejs+express框架，主要程式碼如下：
/**********
body: {
imageString: base64 code
maxSize: w,h
cropOptions: w,h,t,l
}
************/
exports.cropImage = function(req, res) {
var base64Img = req.body.imageString;
if(!/^data:image\/.*;base64,/.test(base64Img)){
res.send({
success: false,
message: 'Bad base64 code format'
});
}
var fileFormat = base64Img.match(/^data:image\/(.*);base64,/)[1];
var base64Data = base64Img.replace(/^data:image\/.*;base64,/, "");
var maxSize = req.body.maxSize;
maxSize = maxSize.split(',');
var cropOptions = req.body.cropOptions;
cropOptions = cropOptions.split(',');
try{
var buf = new Buffer(base64Data, 'base64');
var jimp = new Jimp(buf, 'image/' + fileFormat, function() {
var maxW = parseInt(maxSize[0], 10);
var maxH = parseInt(maxSize[1], 10);
var cropW = parseInt(cropOptions[0], 10);
var cropH = parseInt(cropOptions[1], 10);
var cropT = parseInt(cropOptions[2], 10);
var cropL = parseInt(cropOptions[3], 10);
this.resize(maxW, maxH)
.crop(cropT, cropL, cropW, cropH);
});
jimp.getBuffer('image/' + fileFormat, function(b) {
var base64String = "data:image/" + fileFormat + ";base64," + b.toString('base64');
res.send({
success: true,
source: base64String
});
});
}catch(err) {
logger.error(err);
res.send({
success: false,
message: 'unable to complete operations'
});
}
};
評論(1)