寫在最前：
前兩天老大跟我說老虎官網上那個自定義頭像的功能是flash實現的，沒有安裝過的還得手動去“允許”falsh的運行。所以讓我用canvas實現一個一樣的功能，嘿嘿，剛好最近也在研究canvas，所以欣然答應（其實，你沒研究過難道就不答應么，哈哈哈哈哈~）
成果展示：
Git地址:https://github.com/ry928330/portraitDIY
功能說明：
實現細節：
因為你要對圖片所在的區域進行截圖，所以你得制作一張canvas，蓋在圖片所在的區域。這里，我們給出了一個函數，根據傳入的DOM里面元素的類名創建相同位置的canvas，蓋在原來的DOM元素上面：
function createCanvasByClassName(tag) { var canvasInitialWidth = $('.' + tag).width(); var canvasInitialHeight = $('.' + tag).height(); var left = $('.' + tag).offset().left - $('.' + tag).parent('.portraitContainer').offset().left + 1; var top = $('.' + tag).offset().top - $('.' + tag).parent('.portraitContainer').offset().top + 1; //var left = $('.' + tag).offset().left + 1; //var top = $('.' + tag).offset().top + 1; clearCanvasObj.left = $('.' + tag).offset().left + 1; clearCanvasObj.top = $('.' + tag).offset().top + 1; // clearCanvasObj.left = left; // clearCanvasObj.top = top; var canvasElement = $('<canvas></canvas>'); var randomNum = Math.floor(getRandom(0, 10000)); clearCanvasObj.canvasId = randomNum; canvasElement.attr({ id: 'canvas', width: canvasInitialWidth, height: canvasInitialHeight }); canvasElement.css({ position: 'absolute', top: top, left: left }); //$('body').append(canvasElement); var appendEle = $('.portraitContainer').append(canvasElement); var canvas = document.getElementById('canvas'); var ctx = canvas.getContext('2d'); //ctx.fillStyle = "rgba(211,211,216,0.5)"; ctx.clearRect(0, 0, canvasInitialWidth, canvasInitialHeight); ctx.fillStyle = "rgba(0,0,0, 0.4)"; ctx.fillRect(0, 0, canvasInitialWidth, canvasInitialHeight); return canvas;}有了這張canvas你就可以在你圖片所在區域肆意的操作了。首先，降整個區域畫上一個淺黑色的陰影，然后再擦除初始小方框區域里面的顏色。然后給整個頁面添加mousedown，mousemove，mouseup事件，他們所做的功能就跟你在頁面中實現一個拖拽的功能類似，這里重點說下mousemove里面做的操作，代碼如下：
function mousemoveFunc(event) { /* Act on the event */ var nowMouseX = event.clientX - clearCanvasObj.left; var nowMouseY = event.clientY - clearCanvasObj.top; if (nowMouseX >= clearCanvasObj.xStart && nowMouseX <= clearCanvasObj.xStart + clearCanvasObj.width && nowMouseY >= clearCanvasObj.yStart && nowMouseY <= clearCanvasObj.yStart + clearCanvasObj.height) { clearCanvasObj.isCanvasArea = true; //clearCanvasObj.isRightCorner = false; imgContainerCanvas.style.cursor = 'move'; } else if ((nowMouseX >= clearCanvasObj.xStart + clearCanvasObj.width - 10) && (nowMouseX <= clearCanvasObj.xStart+ clearCanvasObj.width + 10) && (nowMouseY >= clearCanvasObj.yStart + clearCanvasObj.height - 10) && (nowMouseY <= clearCanvasObj.yStart + clearCanvasObj.height + 10)) { clearCanvasObj.isCanvasArea = true; //clearCanvasObj.beginDraw = false; imgContainerCanvas.style.cursor = 'se-resize'; } else { clearCanvasObj.isCanvasArea = false; //clearCanvasObj.isRightCorner = false; imgContainerCanvas.style.cursor = 'default'; } var outerDomWidth = $(".imgContainer").width(); var outerDomHeight = $(".imgContainer").height(); var xDistance = event.clientX - clearCanvasObj.mouseX; var yDistance = event.clientY - clearCanvasObj.mouseY; //var outerCTX = canvas.getContext('2d'); //移動小方框 if (clearCanvasObj.beginDraw && clearCanvasObj.isCanvasArea && !clearCanvasObj.isRightCorner) { ry_CTX.fillStyle = clearCanvasObj.color; // console.log('1', clearCanvasObj.xStart, clearCanvasObj.yStart) ry_CTX.fillRect(clearCanvasObj.xStart, clearCanvasObj.yStart, clearCanvasObj.width, clearCanvasObj.height); //outerCTX.fillRect(0, 0, canvas.width, canvas.height); clearCanvasObj.xStart += xDistance; clearCanvasObj.yStart += yDistance; //判斷方框是否達到邊界 if (clearCanvasObj.xStart <= 0) { clearCanvasObj.xStart = 0; } if (clearCanvasObj.yStart <= 0) { clearCanvasObj.yStart = 0; } if ((clearCanvasObj.xStart + clearCanvasObj.width) >= outerDomWidth) { clearCanvasObj.xStart = outerDomWidth - clearCanvasObj.width; } if ((clearCanvasObj.yStart + clearCanvasObj.height) >= outerDomHeight) { clearCanvasObj.yStart = outerDomHeight - clearCanvasObj.height; } // console.log('2', clearCanvasObj.xStart, clearCanvasObj.yStart) ry_CTX.clearRect(clearCanvasObj.xStart, clearCanvasObj.yStart, clearCanvasObj.width, clearCanvasObj.height); produceSmallPic(clearCanvasObj.xStart+clearCanvasObj.left, clearCanvasObj.yStart+clearCanvasObj.top, clearCanvasObj.width, clearCanvasObj.height, imageURL) clearCanvasObj.mouseX = event.clientX; clearCanvasObj.mouseY = event.clientY; } //拖拽小方框 if (clearCanvasObj.isRightCorner) { ry_CTX.fillStyle = clearCanvasObj.color; ry_CTX.fillRect(clearCanvasObj.xStart, clearCanvasObj.yStart, clearCanvasObj.width, clearCanvasObj.height); var realDistance = Math.min(xDistance, yDistance) clearCanvasObj.width += realDistance; clearCanvasObj.height += realDistance; //拖動時邊界條件的判斷 if (clearCanvasObj.xStart + clearCanvasObj.width >= outerDomWidth) { clearCanvasObj.width = outerDomWidth - clearCanvasObj.xStart; clearCanvasObj.height = outerDomWidth - clearCanvasObj.xStart; } if (clearCanvasObj.yStart + clearCanvasObj.height >= outerDomHeight) { clearCanvasObj.width = outerDomHeight - clearCanvasObj.yStart; clearCanvasObj.height = outerDomHeight - clearCanvasObj.yStart; } if (clearCanvasObj.width <= 10) { clearCanvasObj.width = 10; } if (clearCanvasObj.height <= 10) { clearCanvasObj.height = 10; } ry_CTX.clearRect(clearCanvasObj.xStart, clearCanvasObj.yStart, clearCanvasObj.width, clearCanvasObj.height); produceSmallPic(clearCanvasObj.xStart+clearCanvasObj.left, clearCanvasObj.yStart+clearCanvasObj.top, clearCanvasObj.width, clearCanvasObj.height, imageURL); clearCanvasObj.mouseX = event.clientX; clearCanvasObj.mouseY = event.clientY; } }函數里面，你需要注意拖拽的邊界條件，一個是方框不能拖到圖片所在DOM外的邊界；另外一個就是當你鼠標放在小方框所在的區域改變鼠標的樣式。方框在拖動的過程中，我們不斷重繪方框移動的區域（也就是不斷的畫上陰影），然后在新的位置調用clearRect函數，重新擦出一個小方框出來。在拖拽或是拉伸的過程中，我們會不斷調用produceSmallPic函數，在右邊的容器（每個容器都是一個canvas）里面不斷根據容器大小重繪出所需的頭像。代碼如下：
function produceSmallPic(imageURL,left, top, width, height) { var img = new Image(); img.src = imageURL; var targetCtx = new Array(); var targetCanvas = null; img.onload = function() { portraitGroupsArr.forEach(function(item, index) { targetCanvas = document.getElementById(item.class); targetCtx.push(targetCanvas.getContext('2d')); targetCtx[index].clearRect(0,0, item.width, item.height); targetCtx[index].drawImage(img, left - clearCanvasObj.left, top - clearCanvasObj.top, width, height, 0, 0 , item.width, item.height); }) }}我們說下這個函數的作用，這里我們要注意一個參數imageURL，這個URL是由圖片所在的DOM轉化來的。因為你要把DOM所在的區域變成一張圖片，這樣你才能在利用drawImage函數截取你所需要的區域。所以我們先利用html2canvas庫函數講圖片所在的DOM轉化為canvas，這張canvas的內容是包含你所要截取的圖片的，然后把這張canvas轉化為圖片取得圖片地址imageURL，代碼如下：
html2canvas(document.getElementById('imgContainer'), { onrendered: function(canvas) { var imageURL = canvasTransToImage(canavs); ... }})function canvasTransToImage(canvas) { var imageURL = canvas.toDataURL('image/png'); return imageURL;}接著，你就可以便利右側的canvas容器，講圖片重回到里面了，整個過程就這樣結束，回頭看來是不是很簡單。
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