Question

我正在开发一个在画布上加载，渲染和刷新图像的系统对于我的javascript引擎项目，但当我使用img.onload时，它才能在我能够设置img源之前执行

主要功能：

function addImgToList(canvas, url, sw, sh) {
    TempVar = {s: CheckSlots(canvas, 0)
              };
    that = this.TempVar;

    CurrentGFXElements[canvas].images[TempVar.s] = {
        img: new Image(),
        sw: sw,
        sh: sh,
        sprites: [],
        active: true,
        lx: 0, // last x
        ly: 0, // last y
        ew: 0,
        eh: 0,
        animations: 0
    };
    /*error calculations begins before img has been loaded
    */

    CurrentGFXElements[canvas].images[TempVar.s].img.onload = function (TempVar) {
        calcSprites(canvas, TempVar.s, sw, sh);
    } (TempVar);

    //CurrentGFXElements[canvas].images[TempVar.s].img.src = url;

    CurrentGFXElements[canvas].indexList[TempVar.s][0] = 1;
    return TempVar.s;}

注意：我知道设置src的行已注释

计算功能：

function calcSprites(canvas, slot, sw, sh, height) {
TempVar = {
    h: CurrentGFXElements[canvas].images[slot].img.height,
    w: CurrentGFXElements[canvas].images[slot].img.width,
    x: 0,
    y: 0,
    s: slot
};

TempVar.columns = TempVar.w / sw;
TempVar.rows = TempVar.h / sh;
TempVar.sprites = TempVar.columns * TempVar.rows;

console.log(TempVar);

for (i = 0; i < TempVar.sprites; i++) {
    CurrentGFXElements[canvas].images[slot].sprites[i] = [[TempVar.x, TempVar.y]];
    console.log(CurrentGFXElements[canvas].images[slot].sprites[i]);

    TempVar.x += CurrentGFXElements[canvas].images[slot].sw;

    if (TempVar.x >= (CurrentGFXElements[canvas].images[slot].sw * TempVar.columns)) {
        TempVar.x = 0;
        TempVar.y += CurrentGFXElements[canvas].images[slot].sh;
    }
}

return TempVar;}

可以在这里查看完整的文件:(此链接不是24/7全天候）（跳过顶部代码的注释部分）

http://preview.47chkdyfg0j54s4iwcuw0aw3py5e9udikcegdc7r578ehfr.box.codeanywhere.com:3000/engine/graphics.js

Answer 1

我发现每当你将参数传递给一个匿名函数时会出现错误，如果你为onload分配一个函数，函数会自动激活这个错误：

//will activate instantly
img.onload = someFunction();

//same as above
img onload = function (argument) {//insert code}(argument_to_pass);

//these will work without problems
img.onload = someFunction; //this one should work but not 100% sure

img.onload = function () {//insert code}

img onload尽早执行

1 个答案: