WebEngine refuses to use GPU

Steven Larry

I'm just running a minimal example:

#include <QApplication>
#include <QWebEngineView>
#include <QWebEngineSettings>
#include <QSurfaceFormat>

int main(int argc, char *argv[]) {
    QCoreApplication::setAttribute(Qt::AA_EnableHighDpiScaling);
    QApplication app(argc, argv);

    
    QSurfaceFormat format;
    format.setRenderableType(QSurfaceFormat::OpenGL);
    QSurfaceFormat::setDefaultFormat(format);


    qputenv("QTWEBENGINE_CHROMIUM_FLAGS", "--enable-gpu-rasterization --enable-zero-copy --ignore-gpu-blacklist");

  
    QWebEngineView *view = new QWebEngineView();
    view->settings()->setAttribute(QWebEngineSettings::Accelerated2dCanvasEnabled, true);
    view->settings()->setAttribute(QWebEngineSettings::WebGLEnabled, true);

    view->setUrl(QUrl("https://maps.google.com"));
    view->show();

    return app.exec();
}

And noticed the rendering lags badly. As you can see I already tried setting a bunch of flags to force it to use GPU. Checking chrome://gpu (replace the gooogle maps url with it) shows that hardware acceleration is enabled:

alt text

But when I check the task manager, the WebEngineProcess shows no gpu loading, and the cpu load is very high.

Perplexingly, I wrote a python script on the same machine that runs fine and smooth:

from PyQt5.QtWidgets import QApplication
from PyQt5.QtWebEngineWidgets import QWebEngineView
import sys
from PyQt5.QtCore import QUrl
import os


app = QApplication(sys.argv)

view = QWebEngineView()
print(os.environ.get("QTWEBENGINE_CHROMIUM_FLAGS"))
view.setUrl(QUrl("https://maps.google.com"))
view.show()

sys.exit(app.exec_())

What could be the issue here? Any help would be greatly appreciated.

Steven Larry

Very embarassing but I found out I have to to build in RELEASE mode to have the full GPU acceleration.

In practice that means doing

cmake -DCMAKE_BUILD_TYPE=Release ..

Then run windeployqt again. There should be QWebEngineProcess.exe - if there is QWebEngineProcessd.exe (the d for "debug") that means it is still in debug mode and will be slow.