CODEWITHSUNDEEP
user-interfaceopengl
Krab
Krab

Reputation: 6756

Mixing OpenGL and software rendered GUI

I need to write application where the main content will be OpenGL rendered (something like game engine), but there is no good OpenGL based GUI library similiar to what Qt widgets does (but they are software rendered).

As i browsed the source code of Qt, all painting is done via QPainter and there is even QPainter implementation in OpenGL, but the suppport for multiple graphics backends was dropped in Qt 5, so you can't render Qt Widgets in OpenGL anymore (i don't know why).

The problem is that you can't paint to window surface using both software and hardware rendering. You can have the window associated with OpenGL context or use software rendering. That means if i want to have app with complex GUI with OpenGL based content, i need either paint everything using OpenGL (which is hard because as i said, there is no good GUI library for it), or i can render GUI to image using software rendering (for example Qt) and than load that image as OpenGL texture (probably big performance loss).

Does anyone know any good application that is using software rendered GUI loaded as texture to OpenGL? I need to be sure it will work without some big performance loss, but can't find good example that it will work well even for apps like game engines.

Upvotes: 0

Views: 1014

Answers (1)

Nicolas Repiquet
Nicolas Repiquet

Reputation: 9255

If you take the "render ui to texture then draw a textured quad over my game" route, and are worried about performances, try to avoid transfering the whole texture each frame.

If you think about it :

60fps is not necessary for ui : 30fps is enough, so update it one time out of two.

Most of the time, ui dont change between frames, and if it changes, only a small portion of it do.

ui framework often keep track of which part of the ui is "dirty" and need to be redrawn. If you can get your hand on that, you can stream to the texture only the parts that need to be updated (glTexSubImage2D).

Upvotes: -1

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