Draw rectangle in canvas with loaded pdf file using pdf.js

问题

I am trying to draw rectangle over a pdf file. when i draw rectangle in pdf, rectangle not draw properly.

I want to draw only one rectangle at a time, when i draw new rectangle the old rectangle should be remove, but it is not happening.

Here is my code:-

Rendering code of pdf (Rendering is working properly)

function pdfFile (file) {
pdfjsLib.workerSrc = 'pdf.worker.js';
pdfjsLib.getDocument(file).promise.then(function(pdfDoc) {
  pdf = pdfDoc;
  document.getElementById('page_count').textContent = pdfDoc.numPages;
  showButtonGroup(pdf);
  renderPage(pageNum);
});
} 

 function renderPage(num) {
    pageRendering = true;
    pdf.getPage(num).then(function(page) {
      var viewport = page.getViewport({scale: scale});
      canvas.height = viewport.height;
      canvas.width = viewport.width;
      var renderContext = {
        canvasContext: ctx,
        viewport: viewport
      };
      var renderTask = page.render(renderContext);
      renderTask.promise.then(function() {
        pageRendering = false;
        if (pageNumPending !== null) {
          renderPage(pageNumPending);
          pageNumPending = null;
        }
      });
    });

    document.getElementById('page_num').textContent = num;
}

Mouse move function not working properly

function mouseMove(e) {
    if (drag) {
        ctx.putImageData(pdfPages[pageNum], 0, 0);
        ctx.clearRect(rect.startX, rect.startY, rect.w, rect.h);
        rect.w = ((e.pageX - x) - this.offsetLeft) - rect.startX;
        rect.h = ((e.pageY - y) - this.offsetTop) - rect.startY;      
        ctx.strokeStyle = color;
        ctx.strokeRect(rect.startX, rect.startY, rect.w, rect.h);
        Object.assign(data, {
            x: rect.startX,
            y: rect.startY,
            w: rect.w,
            h: rect.h
        })
        console.log(data);
    }
}

Note

When i enable clearRect and putImageData function then rectangle draw properly but canvas pdf shows empty. Here is the attached image
When only enabled clearRect function then showing multiple rectangle in pdf. Here is the attached image

Thanks,

Vikram

回答1:

Please check the below, need to clear the existing rectangle before creating new

function renderPage(num) {
    pageRendering = true;
    pdf.getPage(num).then(function (page) {
        var viewport = page.getViewport({ scale: scale });
        canvas.height = viewport.height;
        canvas.width = viewport.width;
        var renderContext = {
            canvasContext: ctx,
            viewport: viewport
        };
        var renderTask = page.render(renderContext);
        renderTask.promise.then(function () {
            pageRendering = false;

            //You need to clear the existing rectangle
            pdfPages[num] = ctx.getImageData(0, 0, canvas.width, canvas.height);

            //Now you can draw new rectangle
            drawRectangle(10, 10, 100, 50);
            if (pageNumPending !== null) {
                renderPage(pageNumPending);
                pageNumPending = null;
            }
        });
    });

    function drawRectangle(x, y, w, h) {
        ctx.strokeStyle = color;
        ctx.strokeRect(x, y, w, h);
    }

来源：https://stackoverflow.com/questions/58590845/draw-rectangle-in-canvas-with-loaded-pdf-file-using-pdf-js

标签

javascript

pdf

canvas

pdf.js