Resource Initialization and OpenGL Contexts

Question

We have an OpenGL Application (using Ogre3d and SDL, not directly calling OpenGL) and we are trying to change the Resolution at runtime. It seems that we need to re-initialize our OpenGL context with the new Resolution but a number of items are breaking along the way. On Linux it seems to work for a while, then we get graphical corruption on screen. On Windows it simply crashes the next time we try to render a frame. We have forced the reloading of textures in Ogre, and if we rendering nothing but textures (no 3d models) then this works fine, but any 3d models cause a crash and reloading before rendering them has no effect.

Here is a link to an in depth explanation of Ogre3d calls we are doing: http://www.ogre3d.org/forums/viewtopic.php?f=2&t=62825

All we really need to know is, When re-initializing an Opengl context what resources need to be restored?

Why does adjusting an OpenGL context affect other resources? Is it the way OpenGL works, or did one of the libraries we use introduce this issue? Could we have added this issue without knowing it?

Answer 1

Did you have a look at this forum thread ?

SDL seems to destroy the OpenGL when changing resolution. In this case, all you GL resources are destroyed with the context.

One possible solution would be to create another 'dummy' GL context, sharing resources with you 'real' GL context, and to keep it alive with SDL destroys the 'main' context. This way most of your resources should survive.

Note that some resources can't be shared, textures and VBO are fine, but VAO can't.

Answer 2

OpenGL support was added SDL after its surface code had been established. That's why changing the size of a SDL window is destructive. You were pointed to OpenGL context sharing and its caveats. However I'd avoid the problem alltogether by not using SDL for creating an OpenGL window. You can use all the other facilities SDL provides without a window managed by SDL, so the only thing that would change is input event processing and how the window's created. Instead of SDL I'd use GLFW, which like SDL requires you to implement your own event processing loop, so using GLFW as a drop-in replacement for OpenGL window and context creation is straightforward.