Export atlas PDF failed to print images item on template

Question

I create a template on QGIS which contains some text and images. I render the image using HTML with code:

    <style>
.cropped {
    position: absolute;
    width: 27mm; /* width of container */
    height: 27mm;
    background-size: 256px  144px;
    overflow: hidden; 
    border-radius: 50%;
    border: 0px;
    background-position: center top;
    background-color: #eee;
}
#jpg {    background-image: url('img/[%"photo"%]');

}
</style>
<div>
<div class="cropped" id="jpg"></div>
<div>

The atlas has more than 10K items, when I tried to export the atlas on the folder, most of the images failed to be print on the PDF export file. But if I tried to add images without HTML, it works good on exporting. But actually I will need HTML styling version to print the atlas. What is the best way to solve this?

Answer 1

This is definitely a timing issue of Qt. The PDF generation is faster than the HTML rendering. Whenever I face such problems (missing images in HTML, missing SVGs, partly rendered images, Javascript processing in HTML), I'm using a custom Python "wait" function to pause the printing process.

Put the following Python code in the "Python Macros" section of your project (Project > Properties... > Macros) and enable running macros (Settings > Options > General):

from qgis.core import qgsfunction
from qgis.PyQt.QtCore import QTimer,QEventLoop
@qgsfunction(args=1, group='Custom', usesGeometry=False, referenced_columns=[])
def waitX(values, feature, parent):
    x = values[0]
    loop = QEventLoop()
    QTimer.singleShot(x,loop.quit)
    loop.exec_()
    return 0

To get the HTML completely rendered, you have to inject this expression function somewhere into the printing process. I always put it into the data defined override of the label or HTML item Rendering exclusion option (Rendering > Exclude item from exports). That's why this function returns "0". You have to play with the function argument to increase or decrease sleeping time depending on the content of your HTML.