這次帶給大家怎麼用canvas實作自訂頭像功能,用canvas實作自訂頭像功能的注意事項有哪些,以下就是實戰案例,一起來看一下。
寫在最前面:
前兩天老大跟我說老虎官網上那個自訂頭像的功能是flash實現的,沒有安裝過的還得手動去「允許」falsh的運作。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麼,哈哈哈哈哈~)
成果展示:
Git位址:https://github.com/ry928330/portraitDIY
功能說明:
拖曳左側小方塊,或是滑鼠放在小方塊右下角,點擊拉伸方框,方框覆蓋部分的圖片被自動截取下來,然後再在右側的多個容器裡面重繪。
輸入寬高,自訂你需要訂的頭像大小,目前只支援寬高相同的頭像圖片。
實作細節:
因為你要對圖片所在的區域進行截圖,所以你得製作一張canvas,蓋在圖片所在的區域。這裡,我們給了一個函數,根據傳入的DOM裡面元素的類別名稱創建相同位置的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,然後再擦除初始小方框區域裡面的顏色。然後給整個頁面添加mousedown,mousemove,mouseup事件,他們所做的功能就跟你在頁面中實現一個拖曳的功能類似,這裡重點說下mousemove裡面做的操作,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'); //移动小方框 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; //判断方框是否达到边界 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; //拖动时边界条件的判断 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; } }
函數裡面,你需要注意拖曳的邊界條件,一個是方框不能拖到圖片所在DOM外的邊界;另外一個就是當你滑鼠放在小方框所在的區域改變滑鼠的樣式。方框在拖曳的過程中,我們不斷重繪方框移動的區域(也就是不斷的畫上陰影),然後在新的位置呼叫clearRect函數,重新擦出一個小方框出來。在拖曳或是拉伸的過程中,我們會不斷呼叫produceSmallPic函數,在右邊的容器(每個容器都是一個canvas)裡面不斷根據容器大小重繪出所需的頭像。程式碼如下:
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,這裡我們要注意一個參數imageURL,這個URL是由圖片所在的DOM轉換來的。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函式庫函數講圖片所在的DOM轉換成canvas,這張canvas的內容是包含你所要截取的圖片的,然後把這張canvas轉換成圖片取得圖片地址imageURL,程式碼如下:
html2canvas(document.getElementById('imgContainer'), { onrendered: function(canvas) { var imageURL = canvasTransToImage(canavs); ... } }) function canvasTransToImage(canvas) { var imageURL = canvas.toDataURL('image/png'); return imageURL; }
接著,你就可以方便右邊的canvas容器,講圖片重回裡面了,整個過程就這樣結束,回頭看來是不是很簡單。
相信看了本文案例你已經掌握了方法,更多精彩請關注php中文網其它相關文章!
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