How to stop OpenGL from pausing when the window is out of focus or resizing?

Question

I'm trying to prevent my rendering from stopping when my window is out of focus or resizing. In addition to the resizing, if I resize my window smaller, then bigger again anything that wasn't visible when it was smaller is now black. Is there any way to fix this?

Answer 1

There are really two distinct things going on here. The moving/resizing problem is caused by the windows DefWindowProc function which applications use to handle messages that aren't explicitly handled by the application itself. In the case of moving or resizing, it blocks, creating a new message queue to handle most messages, but there are a few that it will still dispatch to the application's main event queue, like WM_TIMER . You can find lots more information in this answer .

The second issue is that your program only "owns" the pixels inside your window, and only those that are not covered up by other windows. When you make the window smaller, the pixels at the edge need to be overwritten to show the window border or whatever's behind the window. When the window is made bigger, some drivers automatically set the newly acquired pixels to black, while others leave them at whatever they were before (usually part of the window border). The OS doesn't remember if those pixels had some specific color the last time the window was that size, because most of the time the program doesn't care. Instead, windows sends a WM_PAINT message to indicate that the application should redraw the window. Your program should either directly handle this, or use a library like GLFW that abstracts it. In addition, you need to handle resize events by calling glViewport with the new size of the window.