var pdfjsLib = window['pdfjs-dist/build/pdf'];


function renderPage() {

    document.getElementById('pdfprogress').innerHTML = 'Идет подготовка страницы ...';

    pageRendering = true;
    // Using promise to fetch the page
    pdfDoc.getPage(pageNum).then(function(page, ) {

    var canvas = document.getElementById('the-canvas');  
    var context = canvas.getContext('2d');
      var viewport = page.getViewport({scale: scale});
      canvas.height = viewport.height;
      canvas.width = viewport.width;
  
      // Render PDF page into canvas context
      var renderContext = {
        canvasContext: context,
        viewport: viewport
      };
      var renderTask = page.render(renderContext);
  
      // Wait for rendering to finish
      renderTask.promise.then(function() {
        pageRendering = false;
        if (pageNumPending !== null) {
          // New page rendering is pending
          renderPage(pageNumPending);
          pageNumPending = null;
        }
      });
    });
    
    document.getElementById('zoompdf').innerHTML = scale + 'x';
    document.getElementById('pdfprogress').innerHTML = 'Приятного чтения ↓';

    if (typeof prevlink !== 'undefined') 
        document.getElementById('prevbutton').href = prevlink + '/'+ scale;
    
    if (typeof nextlink !== 'undefined')    
        document.getElementById('nextbutton').href = nextlink + '/'+ scale;
}  


function pdfzoomin(){

    scale += 0.25;
    renderPage();

}

function pdfzoomout(){

    scale -= 0.25;
    renderPage();

}

function startpdfviewer(){
    
    pdfjsLib.getDocument(url).promise.then(function(pdfDoc_) {
        pdfDoc = pdfDoc_;
        renderPage();
    });
    
}