I blit to the window on the next line after resizing it. It only sets the window size once. It doesn’t need to be draggable by the user. It flickers on the part that was added to the window, and on some occasions has the whole window flicker some kind of inverese image of the contents. It’s tested on Windows 7 and uses Java. Is there something to do about the timing of the resize? It uses a locked frame rate that starts going when the program opens.
Resizing any window to be larger on my Windows 10 system, including a GLFW window, causes a brief flicker on the new part of the window, but nothing as extreme as you mention. The Desktop Window Manager has changed significantly since Windows 7 however.
I believe the framebuffer (the part OpenGL draws to when not using a different render target) resizing occurs during the buffer swapping, i.e.
glfwSwapBuffers(). To get the cleanest resize possible after a buffer swap you can call
glfwGetFramebufferSize() and then render using this size.