this post was submitted on 06 Jun 2025
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Okay, am I understanding this correctly? In Y-up right-hand, positive X is "to the left"?
I personally think that right-hand Z-up makes the most sense, but it makes sense to move to where most of the industry is going.
Z is depth. Why should it ever be up? Honest question.
Camera space vs world space.
Personally z up is the only one that makes sense.
It depends if you view the X-Y plane as the camera/viewport/screen or the ground. If X-Y is the ground, then Z is either up or down.
Ahh ofc
For cameras, the convention is Z depth but right handed:
From the chart I would guess that in Y-up right-hand positive X is to the right. You look at the palm of your hand.
That way when you develop a 2d platformer you would use a standard XY coordinate system. Switching to 3d would logically add the z axis as depth and not height. A movie is usually shot that way as well.
Of course that analogy breaks down as soon as your base-game is top down. Like a city planer or so.
Anyways, with standards it's often best to just go with what most others do. So kudos to Unreal for not being stubborn.
He references "Left-Up-Forward", so X is Left, Z is into the screen.
2D is not a consideration, even if it'd be logical. (That's where Left-handed Right-Up-Forward grows out of.)
I don't think that's correct. Here's a drawing I did when trying to get my head around this.
drawing
I find that trying to make sense of terms like "to the left" tricky when we can rotate the directional cube any way we want. For example, in my drawing for "Y-up, left handed", the red X axis is pointed leftwards. However, we could rotate the unit vector cube so that the X axis is pointed right, and the Y axis is pointing up (i.e. the orientation we're most familiar with for 2D graphs). The Z axis would then be pointing away from us, into the plane of the paper/screen.
In contrast, if we oriented the Y-up right-handed cube in the same way, then the Z axis would be oriented as if to come out of the plane of the screen/page, towards us.
These distinctions only matter when we add a third dimension, so the left or right handedness is basically a question of "when we add the third axis to a 2D square made by the other two axes, does the third axis come towards us or away from us? I apologise if this hasn't made things any clearer — I am able to make things make sense by imagining the rotations in my head, but not everyone is able to visualise them like that.