I sent a blender file I made to another member of this forum for texturing.
When I received the modified file and booted it up, there is a red box in the center of the screen that only renders within that box.
How do I get rid of it so I can render the entire screen?
Assuming that you want to make an actual render, press F12. If you just want to preview the whole screen and clear the render border, press CTRL + ALT + B. Next time, do a google search, many problems have already been awnsered.
