canvas之自定義頭像功能實現

ryyyyy發表於2017-09-28
Canvas

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的執行。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麼，哈哈哈哈哈~）

  對了，大佬們記得給我的部落格點贊，要星星哦~

成果展示：

Git地址:

github.com/ry928330/po…

功能說明：

  1. 拖拽左側小方框，或者是滑鼠放在小方框右下角，點選拉伸方框，方框覆蓋部分的圖片被自動擷取下來，然後再在右側的多個容器裡面重繪。
  2. 輸入寬高，自定義你需要訂製的頭像大小，目前只支援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，所以你得製作一張canvas，蓋在圖片所在的區域。這裡，我們給出了一個函式，根據傳入的DOM裡面元素的類名建立相同位置的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;
}複製程式碼

  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。然後給整個頁面新增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，這裡重點說下mousemove裡面做的操作，程式碼如下：

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;
    }                            
}複製程式碼

  函式裡面，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；另外一個就是當你滑鼠放在小方框所在的區域改變滑鼠的樣式。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），然後在新的位置呼叫clearRect函式，重新擦出一個小方框出來。在拖拽或是拉伸的過程中，我們會不斷呼叫produceSmallPic函式，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);
        })
    }
}複製程式碼

  我們說下這個函式的作用，這裡我們要注意一個引數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函式擷取你所需要的區域。所以我們先利用html2canvas庫函式講圖片所在的DOM轉化為canvas，這張canvas的內容是包含你所要擷取的圖片的，然後把這張canvas轉化為圖片取得圖片地址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;
}複製程式碼

  接著，你就可以便利右側的canvas容器，講圖片重回到裡面了，整個過程就這樣結束，回頭看來是不是很簡單。

相關依賴：

<script src="https://cdn.bootcss.com/html2canvas/0.5.0-beta4/html2canvas.min.js"></script>複製程式碼

寫在最後：

  canvas的操作，要多多注意那些邊界條件，什麼時候該重繪什麼時候該清除，這些是比較重要的。邏輯清晰了，canvas本身的API也就那麼幾個，操作起來也就沒那麼麻煩了，最後，謝謝大家查閱，寫的不是很清楚，有不懂的可以一起討論~

相關文章