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：
- 拖拽左側小方框，或者是鼠標放在小方框右下角，點擊拉伸方框，方框覆蓋部分的圖片被自動截取下來，然后再在右側的多個容器里面重繪。
- 輸入寬高，自定義你需要訂制的頭像大小，目前只支持寬高相同的頭像圖片。
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;
}
}
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