如何制作可以填充矢量图像背景的预加载器？

Question

有人可以解释我如何从矢量图像中制作 css3 preloader 。我想实现这个目标： 在开始时，徽标是透明的，只有边框可见，以及如何完成加载，徽标从底部到顶部填充背景。

非常感谢你的帮助。

Answer 1

有几种方法可以做你要求的。

由于您标记为canvas，因此此处为canvas版本：

此演示使用context.drawImage的剪切版本仅绘制画布底部的部分图像。动画循环会增加随时间显示的图像数量。

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// canvas related variables
var canvas=document.getElementById("canvas");
var ctx=canvas.getContext("2d");
var cw,ch;

// load the logo and the logo outline
// then start the animation
var logoOutline;
var logo=new Image();
logo.onload=start;
logo.src='https://dl.dropboxusercontent.com/u/139992952/multple/marioStanding.png';
function start(){

    logoOutline=outlinePNG(logo,'lightgray');

    cw=canvas.width=logoOutline.width;
    ch=canvas.height=logoOutline.height;
    canvas.style.border='1px solid red';
    
    logo.displayY=logo.height-2;
    
    requestAnimationFrame(animate);
}


function animate(time){

    // cache logo.displayY into a variable b/ it's used often
    var y=logo.displayY;

    // clear the logo canvas
    ctx.clearRect(0,0,cw,ch);

    // use the clipping version of drawImage to 
    // increasingly reveal the logo from the bottom
    ctx.drawImage(logo,
        0,y,logo.width,logo.height-y,
        2,y+2,logo.width,logo.height-y);

    // reduce .displayY which increases the reveal
    logo.displayY--;
    
    // request another loop if the entire logo has not been revealed
    if(logo.displayY>0){
    
        // draw the outline
        ctx.drawImage(logoOutline,0,0);
    
        // request another loop until the logo is fully displayed
        requestAnimationFrame(animate);
    }
    
}

//
// Attribution Ken Fyrstenberg
// http://stackoverflow.com/questions/25467349/in-a-2d-canvas-is-there-a-way-to-give-a-sprite-an-outline/27127273#27127273
function outlinePNG(img,outlineColor){
    // new canvas sized to image size + 2px on each side
    var c=document.createElement('canvas');
    var cctx=c.getContext('2d');
    c.width=img.width+4;
    c.height=img.height+4;
    // redraw the image with 8-way offsets (n,s,e,w,nw,ne,se,sw)
    cctx.translate(2,2);
    cctx.drawImage(img, -2, -2);
    cctx.drawImage(img,  0, -2);
    cctx.drawImage(img,  2, -2);
    cctx.drawImage(img, -2,  0);
    cctx.drawImage(img,  2,  0);
    cctx.drawImage(img, -2,  2);
    cctx.drawImage(img,  0,  2);
    cctx.drawImage(img,  2,  2);
    cctx.translate(-2,-2);
    // fill with color
    cctx.globalCompositeOperation="source-in";
    cctx.fillStyle=outlineColor;
    cctx.fillRect(0,0,img.width+4,img.height+4);   
    // draw original image in "erase" mode
    cctx.globalCompositeOperation = "destination-out";
    cctx.drawImage(img,2,2);
    // return the outline canvas
    return(c);
}

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<canvas id="canvas" width=300 height=300></canvas>

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