onload前面加async

在使用`onload`事件时，可以在前面加上`async`关键字来使成为异步函数。这做的目的是让`onload`事件在加载资源时不会阻塞页面的其他操作。以下是一个示例：

<script>
  window.onload = async function() {
    // 异步操作
    await someAsyncFunction();
    console.log("页面加载完成");
  }
</script>

通过在`onload`函数前加上`async`关键字，我们可以在其中使用`await`来等待异步操作完成。这样，当页面加载完成后，才会执行后续的代码逻辑。这种方式可以避免阻塞页面加载，提升用户体验。

相关问题

private async parseMaterial(osgStateSet: any) { let material = new THREE.MeshBasicMaterial({ // side: THREE.DoubleSide, }); //THREE.FrontSide 背面 // THREE.BackSide 前面 // THREE.DoubleSide 双面 let osgImage = osgStateSet.TextureAttributeList[0].value.StateAttribute.Image; // let texture = this.parseImage(osgImage); let fileName = osgImage.Name; const isJPEG = fileName.search(/.jpe?g($|?)/i) > 0; const isPNG = fileName.search(/.png($|?)/i) > 0; if (!isPNG && !isJPEG) { return; } let mimeType = isPNG ? 'image/png' : 'image/jpeg'; let imageUri: any = new Blob([osgImage.Data], { type: mimeType }); let base64 = await this.blobToBase64(imageUri); // debugger let imageUrl: any = URL.createObjectURL(imageUri); try { let texture = new THREE.TextureLoader().load(base64, () => { texture.needsUpdate = true; // texture.format = THREE.RGBAFormat; texture.type = THREE.UnsignedShort5551Type; texture.minFilter = THREE.LinearMipmapNearestFilter; texture.magFilter = THREE.LinearMipmapNearestFilter; texture.generateMipmaps = false; // texture.format = THREE.RGBAIntegerFormat; // texture.minFilter = THREE.NearestFilter; // texture.magFilter = THREE.NearestFilter; // texture.minFilter = THREE.LinearMipMapLinearFilter; // texture.magFilter = THREE.LinearFilter; // texture.wrapS = THREE.RepeatWrapping; // texture.wrapT = THREE.RepeatWrapping; // texture.anisotropy = 1; // texture.generateMipmaps = false; // texture.encoding = THREE.sRGBEncoding; }); imageUri = null; osgImage = null; imageUrl = null; if (texture) { material.map = texture; } } catch (e) { console.log('纹理加载出错', e); } osgStateSet = null; return material; } private blobToBase64(blob: any) { return new Promise((resolve, reject) => { const fileReader = new FileReader(); // readAsDataURL fileReader.readAsDataURL(blob); fileReader.onload = (e: any) => { resolve(e.target.result); }; }); }没有显示base64图片的纹理，也没有报错，请找出问题，并给出详细代码

在代码中，你使用了一个Blob对象来加载纹理图片，并将其转换成了base64编码，但是在加载纹理时，却直接使用了base64编码字符串来加载纹理，这个可能是导致问题的原因。正确的做法应该是使用图片的URL来加载纹理，而不是直接使用base64编码字符串。

具体修改代码如下：

private async parseMaterial(osgStateSet: any) {
    let material = new THREE.MeshBasicMaterial({
        // side: THREE.DoubleSide,
    });
    //THREE.FrontSide 背面
    // THREE.BackSide 前面
    // THREE.DoubleSide 双面

    let osgImage = osgStateSet.TextureAttributeList[0].value.StateAttribute.Image;
    // let texture = this.parseImage(osgImage);

    let fileName = osgImage.Name;
    const isJPEG = fileName.search(/.jpe?g($|?)/i) > 0;
    const isPNG = fileName.search(/.png($|?)/i) > 0;
    if (!isPNG && !isJPEG) {
        return;
    }
    let mimeType = isPNG ? 'image/png' : 'image/jpeg';
    let imageUri: any = new Blob([osgImage.Data], { type: mimeType });

    try {
        // 使用图片的URL来加载纹理
        let texture = await new Promise<THREE.Texture>((resolve) => {
            let imageUrl = URL.createObjectURL(imageUri);
            new THREE.TextureLoader().load(imageUrl, (texture) => {
                // 在加载完成的回调函数中，手动释放URL对象，避免内存泄漏问题
                URL.revokeObjectURL(imageUrl);
                texture.needsUpdate = true;
                // texture.format = THREE.RGBAFormat;
                texture.type = THREE.UnsignedShort5551Type;
                texture.minFilter = THREE.LinearMipmapNearestFilter;
                texture.magFilter = THREE.LinearMipmapNearestFilter;
                texture.generateMipmaps = false;
                // texture.format = THREE.RGBAIntegerFormat;
                // texture.minFilter = THREE.NearestFilter;
                // texture.magFilter = THREE.NearestFilter;
                // texture.minFilter = THREE.LinearMipMapLinearFilter;
                // texture.magFilter = THREE.LinearFilter;
                // texture.wrapS = THREE.RepeatWrapping;
                // texture.wrapT = THREE.RepeatWrapping;
                // texture.anisotropy = 1;
                // texture.generateMipmaps = false;
                // texture.encoding = THREE.sRGBEncoding;
                resolve(texture);
            });
        });

        if (texture) {
            material.map = texture;
        }
    } catch (e) {
        console.log('纹理加载出错', e);
    }
    osgStateSet = null;
    return material;
}

private blobToBase64(blob: any) {
    return new Promise((resolve, reject) => {
        const fileReader = new FileReader();
        // readAsDataURL
        fileReader.readAsDataURL(blob);
        fileReader.onload = (e: any) => {
            resolve(e.target.result);
        };
    });
}

其中，使用了一个Promise对象来等待纹理加载完成后返回，同时在加载完成的回调函数中，手动释放URL对象，避免内存泄漏问题。另外，建议在加载纹理时，设置合适的minFilter和magFilter，以获得更好的渲染效果。