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When I change to windowed mode in the paint app I made, the texture page is put on the surface again. Not sure why this has happened again. Full screen is working like easy cake.
Suggests you're not clearing the surface before drawing to it. Every time you change anything related to the window (drag, fullscreen, size, etc...) all surfaces are cleared and recreated, so they'll occupy a different space in memory each time. If you don't clear the surface after this, then it will hold whatever was in the position in memory beforehand.
if !surface_exists(global.final_surf)
{
surface_create(room_width,room_height)
}
if surface_exists(global.final_surf)
{
surface_free(global.final_surf)
}