canvas自定义头像功能实现代码示例分析

来源：www.45fan.com 2017-11-14 11:41:11

写在最前：

前两天老大跟我说老虎官网上那个自定义头像的功能是flash实现的，没有安装过的还得手动去“允许”falsh的运行。所以让我用canvas实现一个一样的功能，嘿嘿，刚好最近也在研究canvas，所以欣然答应（其实，你没研究过难道就不答应么，哈哈哈哈哈~）

成果展示：

canvas自定义头像功能实现代码示例分析

Git地址:https://github.com/ry928330/portraitDIY

功能说明：

拖拽左侧小方框，或者是鼠标放在小方框右下角，点击拉伸方框，方框覆盖部分的图片被自动截取下来，然后再在右侧的多个容器里面重绘。
输入宽高，自定义你需要订制的头像大小，目前只支持宽高相同的头像图片。

实现细节：

因为你要对图片所在的区域进行截图，所以你得制作一张canvas，盖在图片所在的区域。这里，我们给出了一个函数，根据传入的DOM里面元素的类名创建相同位置的canvas，盖在原来的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;
}

有了这张canvas你就可以在你图片所在区域肆意的操作了。首先，降整个区域画上一个浅黑色的阴影，然后再擦除初始小方框区域里面的颜色。然后给整个页面添加mousedown，mousemove，mouseup事件，他们所做的功能就跟你在页面中实现一个拖拽的功能类似，这里重点说下mousemove里面做的操作，代码如下：

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;
  }              
}

函数里面，你需要注意拖拽的边界条件，一个是方框不能拖到图片所在DOM外的边界；另外一个就是当你鼠标放在小方框所在的区域改变鼠标的样式。方框在拖动的过程中，我们不断重绘方框移动的区域（也就是不断的画上阴影），然后在新的位置调用clearRect函数，重新擦出一个小方框出来。在拖拽或是拉伸的过程中，我们会不断调用produceSmallPic函数，在右边的容器（每个容器都是一个canvas）里面不断根据容器大小重绘出所需的头像。代码如下：

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);
    })
  }
}

我们说下这个函数的作用，这里我们要注意一个参数imageURL，这个URL是由图片所在的DOM转化来的。因为你要把DOM所在的区域变成一张图片，这样你才能在利用drawImage函数截取你所需要的区域。所以我们先利用html2canvas库函数讲图片所在的DOM转化为canvas，这张canvas的内容是包含你所要截取的图片的，然后把这张canvas转化为图片取得图片地址imageURL，代码如下：

html2canvas(document.getElementById('imgContainer'), {
    onrendered: function(canvas) {
      var imageURL = canvasTransToImage(canavs);
      ...
    }

})
function canvasTransToImage(canvas) {
  var imageURL = canvas.toDataURL('image/png');
  return imageURL;
}

接着，你就可以便利右侧的canvas容器，讲图片重回到里面了，整个过程就这样结束，回头看来是不是很简单。

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canvas自定义头像功能实现代码示例分析

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