Qt WebEngine requires hardware acceleration to merge page layers, and you probably won’t be able to see anything on the screen without it.
Chromium, behind Qt WebEngine, is quite a beast and more designed for perceived smoothness than for getting processor cycles; he will use all the resources necessary to achieve this.
JavaScript WebGL , GPU, GL . WebGL FBO, , GL, , Chromium, , , , QtQuick .
, JavaScript WebGL , OpenGL . 30% , .
, , - QtQuick, : http://qt-project.org/doc/qt-5/qtquick-scenegraph-customgeometry-example.html, , 10% .