A-Frame+pdf.js：只有在VR模式下才能更新画布纹理两次

这个问题的解决方法是在A-Frame场景中使用pdf.js来加载PDF文件，但在VR模式下，无法更新画布纹理两次。解决方案是调用“pdf.js”中的“PDFJS.disableWorker = true;”命令来禁用“worker”，使其在单线程环境中工作。这种方法已在下面的示例代码中说明。

示例代码：

AFRAME.registerComponent('pdf', { schema: {src: {type: 'string'}},

init: function () { var self = this; var el = this.el;

PDFJS.workerSrc = '//mozilla.github.io/pdf.js/build/pdf.worker.js';
PDFJS.disableWorker = true;

PDFJS.getDocument(this.data.src).then(function (doc) {
  self.doc = doc;
  el.emit('pdf-loaded');
});

},

getPageDimensions: function (pageNumber) { var pdfPage = this.doc.getPage(pageNumber); var viewport = pdfPage.getViewport(1); return {width: viewport.width, height: viewport.height}; } });

AFRAME.registerComponent('pdf-page', { schema: {pageNumber: {type: 'number', default: 1}},

init: function () { var el = this.el; var dimensions = el.sceneEl.components.pdf.getPageDimensions(this.data.pageNumber); el.setAttribute('geometry', 'primitive: plane; height: ' + dimensions.height * 0.01 + '; width: ' + dimensions.width * 0.01); el.setAttribute('material', 'shader: flat; side: double'); this.renderPage(); },

renderPage: function () { var self = this; var el = this.el;

this.el.sceneEl.components.pdf.doc.getPage(this.data.pageNumber).then(function (page) {
  var viewport = page.getViewport(1);

  var canvas = document.createElement('canvas');
  var context = canvas.getContext('2d');
  var cssScale = 1 / viewport.scale;

  canvas.height = viewport.height * cssScale;
  canvas.width = viewport.width * cssScale;

  var task = page.render({canvasContext: context, viewport: viewport});

  task.promise.then(function () {
    el.setAttribute('material', 'src: ' + canvas.toDataURL());
  });
});

} });