The Seven Voyages Of Steve
Yes, I *still* have to look this up sometimes because I've used and made so many engines and tools that I don't know which hand is which and which way is up half the time ;) Gotta laugh at UE in the corner on its own there.
Ogre was right-handed (aka the canonical way if like me you learned from the Red Book) but had no concept of "up", technically. It could be whatever you wanted 🤷♂️
WildRikku
@sinbad oh no, I only knew a smaller version of that diagram. Crap. So if I learn Houdini I'll have to deal with yet another system...
Krafter
@sinbad I queried the search engines for a while and never managed to find out why. Why would UE choose this coordinate system, breaking everyone's expectations about where axis should be, all three in my case.
The Seven Voyages Of Steve
@kr4ft3r I can understand Z up, it makes 2D only calculations more sensible (truncate 3 items to 2, instead of having to swizzle XYZ to XZ like in Unity. Left hand coordinates are usually because people want positive coords to go into the screen not behind you
Rune Skovbo Johansen
@sinbad @kr4ft3r Except for 2D (and 2.5D) platformers where you can truncate in Unity and have to swizzle in the Z=up engines.
The Seven Voyages Of Steve
@runevision @kr4ft3r yeah UE was never designed for 2D games
Krafter
@sinbad That's all fine but I can't grasp the reason behind X forward, which also implies that X would be vertical in 2D, idk about real mathematicians but this is the opposite from what most coders expect.
The Seven Voyages Of Steve
@kr4ft3r when +Z is up and left handed, +X being forward makes +Y the right vector. People like positive bases
Krafter
@sinbad Well thanks, that makes sense. Still doesn't explan why UE chose to be sitting alone over there, could it be some programmer's decades old arbitrary decision or was there a proper reason, I guess former and can leave it at that.
The Seven Voyages Of Steve
@kr4ft3r bear in mind this was decided by Tim Sweeny in 1998 before most of the others were even made, so you could say they all just decided to do something else
The Seven Voyages Of Steve
@kr4ft3r also all the choices are arbitrary, none of them are right or wrong - most math texts tend to be right-handed but even MS threw that out the window because they wanted increasing depth to be +Z
Ric
@sinbad @kr4ft3r in a WYSIWYG editor, I'll agree. But in code-only editors, Y up is the only way 3D makes sense to me. You're looking at a screen of X,Y units and adding a depth to it. You even have Z buffering to log the depth of a thing the further into the screen it goes. I can't fathom why anybody would then think it best to flip that organic axis over and have Z pointing upwards. 😣
The Seven Voyages Of Steve
@dev_ric @kr4ft3r it all depends on whether you’ve been thinking about 2D side-on or top-down. Side on and the extra dimension (Z) is depth, but for top-down the extra dimension is height. All a matter of perspective and previous assumptions
Simon Carter
@sinbad @runevision @kr4ft3r I think Magic Carpet, Dungeon Keeper and Fable were all the same coordinate system as UE. The thinking was indeed “it’s just top-down 2D, but you can also zoom in and out.”
The Seven Voyages Of Steve
@kr4ft3r @bbbscarter @runevision yeah exactly - imagine drawing your top-down dungeon maps on graph paper, as so many of us old folks did - that’s canonically an XY coordinate system. Need to add height, use the next letter along 😃
Krafter
@bbbscarter @sinbad @runevision @dev_ric If, on top of the top-down-first approach we also imagine that the game designer likes their top-down figures to face to the right, this may hold some excuse for why X+ is forward. I guess.
Jeremiah Fieldhaven
@sinbad So I build and UV models in Lightwave, export them into Blender to rig, animate, and export the .fbx, and then import into Unreal.
Maybe I should add a stage involving Maya or something so I can get all four corners crossed off....
Simon Carter
@sinbad @kr4ft3r @runevision yup, exactly that. I’ll be honest, it’s still the most intuitive coordinate system for me, even though I know better - for many 3D games you do the initial map editing top down, like it’s a board game, and then raise/lower things.
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