What happens to blacklisted graphic cards in Qt 5.6 when running a QML app?

The upcoming Qt 5.6 introduces a blacklist to mark some graphic cards which are known to insufficiently support OpenGL or Angle.

Confirm e.g.

But what happens to QML apps on cards that have both disable_desktopgl and disable_angle set? Can those users not run QML apps at all?

Solution

They can't use OpenGL to accelerate Qt Quick, no. Which is a pretty severe drawback. Unfortunately the status of OpenGL on Windows is a nightmare. The "average" Windows computer will have an Intel-based GPU with ancient drivers, which are buggy enough to cause Qt not even try to use any 3D at all (OpenGL nor Direct3D). NVIDIA and AMD are usually better, as at least they tend to be more up-to-date.

Usually upgrading the Intel drivers solves most issues, but you are not always in the position of asking your users to upgrade their drivers (they might not even be able to do so, for instance lacking administrator privileges, and/or using laptops where the driver version has been pinned by the vendor).

Note that even other projects, such as Chromium or Firefox, have their own fine-grained driver bug blacklists (example).

In case your card is totally blacklisted you can:

use an OpenGL CPU implementation, such as Mesa. If you ship opengl32sw.dll with your application, it can be picked up by Qt. See the explaination here.
use the Qt Quick 2D renderer, which is a specialized CPU-based renderer for a subset of Qt Quick items. Compared to Mesa it's incredibly faster (because it doesn't need to go through the OpenGL pipeline in order to draw, say, a rectangle -- it can just draw the rectangle using a 2D rasterizer); on the other hand, certain things stop working, like shader effects. Currently it's available only under a commercial license, but in 5.8 it's going to be open source.

(Nitpick: QML is the language, Qt Quick is the framework/library to build UIs which you program using QML).