What happens when Qt is compiled with no-angle and -no-opengl?

Question

Recently I tried to compile my Qt static libraries with both -no-angle and -no-opengl. I first thought that it would not compile. But unexpectedly, Qt (5.7) compiled just fine. I could also compile my application (using many QtWidgets).

To my surprise I could not see any difference with my Angle based Qt app. No lags, no glitches, my QtCharts were displaying as always.

I could not find any definitive answer on the web. but I have two guesses:

• I was not really using any hardware acceleration after all.
• There is a mysterious fallback mechanism.

What is going on here ?

Answer 1

What happens? In your case nothing. Qt widgets don't use OpenGL behind your back. You have to explicitly force its use in a given widget stack by using the QOpenGlWidget as the top level widget. By default, you're using the CPU-based raster rendering backend - as you noted, it performs quite well.

Compiling Qt without angle and OpenGL support is a good way to make your application smaller if you don't use OpenGL :)