On 2025-01-09 12:00, Mischa Baars wrote: > On Mon, Jan 6, 2025 at 4:41 PM Michel Dänzer > <michel.daenzer@xxxxxxxxxxx <mailto:michel.daenzer@xxxxxxxxxxx>> > wrote: > >> I'm sort of a fan of Michael Abrash, as he inspired me to learn >> programming assembly language a long time ago, but in his Graphics >> Programming Black Book, Chapter 23 <https://www.phatcode.net/ >> res/224/files/html/ch23/23-03.html#Heading6> he shows how the CRTC >> Index Register is used to change what is shown on the screen by >> alternating between two memory pages at PAGE0_OFFSET and >> PAGE1_OFFSET. That's much lower level than OpenGL. OpenGL implementations can and do internally use page flipping under the right circumstances, it cannot be enforced via OpenGL / GLX / EGL APIs though, it's an implementation detail. > The glDrawBuffer() <https://registry.khronos.org/OpenGL-Refpages/gl4/ > html/glDrawBuffer.xhtml> reference page however does speak of > initial values for double buffered contexts and the use of both > front and back buffers. The OpenGL app can use single-buffered drawing to GL_FRONT if it doesn't care about the artifacts possible without double buffering. > Can you explain to me why we are only drawing in GL_BACK and how > that relates to what portion of memory is shown on the screen? A big point of GL_BACK (and double buffering in general) is that it's not what's currently visible on screen, so there can be no artifacts due to visible unfinished frame contents. -- Earthling Michel Dänzer \ GNOME / Xwayland / Mesa developer https://redhat.com \ Libre software enthusiast
