Jim StormdancerPico-8 arranges coordinates with 0, 0 in the top left corner of the screen and y increasing as you go down. But that's a very retrocomputing-inspired design decision! Mathematicians and modern 3D engines and, like, average people looking at graphs, and even some 2D engines think 0, 0 is at the center of the screen and increasing Y means up.
My first computer was a Commodore 64, so I'm very comfortable with increasing Y meaning down. For one code base I worked on I used a graphics library that defaulted to "increasing y up" and I "fixed" it by changing the camera matrix so that increasing y was down, but that didn't fix "increasing V is up" on the texture maps so thinking about every non-trivial texture operation was a complete nightmare and now other people have to maintain that code. Sorry!
My brain is forever locked into "increasing Y is down" but I don't believe in it. I don't believe it's actually right despite using it all the time. On the other hand, I believe strongly and can articulate a specific argument that the Z axis should be up/down despite never having used in an engine that works that way.
Fabian Giesen@mogwai_poet +x right +y down +z into ftw
CremAdanac@mogwai_poet If you look down at the surface of water and maintain that z should increase with depth (going away in 3d) Right hand rule dictates a Y increasing downwards. OTH if you want Z to increase with elevation Y should increase up. It's all about perspective.
@mogwai_poet For texture maps it doesn't make a difference whether +v is up or down as long as it matches the order you upload textures in. (The only place where you can tell is render targets.)
@mogwai_poet E.g. classic D3D order is +u = right, +v down vs. classic GL +s = right, +t up, but it doesn't make a difference in practice, because both agree that the origin is at (0,0) and textures are row-major stored in order of increasing v/t, respectively. The same data in memory works for both.
It only gets messy when you get it in your head that GL usually drawing textures with (0,0) at bottom left and +t going up and D3D with (0,0) at top left and +v down means you should do something.
@mogwai_poet It does mean that if you have say text in a texture map, author a model+texture somewhere with GL conventions, and then look at texture preview in something with D3D conventions, it might show flipped in that preview; however if you have a texture mapped to a model that texture will render the same on both.
@rygorous Yeah, I was already preprocessing the textures, I could've just flipped 'em over