Questionable Content

Here are a few questions, there are no right answers (except for the one with a right answer), and please choose the first answer that comes to you:

What are the primary colors?

A. Red, yellow, blue

B. Red, green, blue

You’re making a 3D model of some object. Which way is up in your world?

A. +Y

B. +Z

What color is chartreuse?

A. Green-yellowish

B. Red-orangish

You write out a 4×4 transform matrix to translate an object. You put the translation values:

A. in the bottom row

B. in the right column

All for now, my opinions and theories tomorrow (though feel free to comment before then).

Update: “answers” here.


  1. wforl’s avatar

    Well, Crytek uses Z-up, so that MUST be the right anwer :p

    When people plot 2d graphs, you’ll always see it plotted against X and Y. X is always known as “Across” and Y as “Up”, so extending upon this concept with another dimension (Z), this should be Depth? no? …. seeing as “Up” and “Across” are already taken. I think working in 2d where Y is Up and 3d where Z is up just confuses things. I guess this all depends on your perspective though, i.e. are your viewing that graph as say a painting on the wall, or the carpet on the floor. In whixh case the opposite would apply. Oh cruel world ! stop confusing me !

    I kinda think the same thing for the last question. Why have 2 different standards thats essentially lead to the same result just with different looking calculations? It just confuses matters when it needn’t.

  2. Sander van Rossen’s avatar

    For me it’s
    1. RGB
    2. +Y
    3. C (== I’ve never even heard of chartreuse!)
    4. A

  3. reavenk’s avatar

    It used to be RYB from K through 12 in art class, then when I started doing computer graphics it was RGB, and for the longest time I didn’t know why it changed until wikipedia taught me the difference between subtractive and additive color wheels.

    It used to be +Y was up back in school while I was learning to program, all the student and teachers had this unspoken agreement that that was the de facto. When I got a job, it was Z+, and 4 years later I’m still not used to it.


    Right Column – just because it’s easier for me the visualize the matrix in column form.

  4. sigmel’s avatar

    1. RGB – I’ve always been around computers, I suppose
    2. +Y – Though I can see wanting to use Z+, especially when dealing with 3D textures
    3. A – Never knew there was an red-orangish version
    4. A – Just been preferential to row major matrices all my life

  5. jonogibbs’s avatar

    A, A, A, A!

  6. kmadsen’s avatar

    Magenta, yellow, cyan is for painters, and RGB is better.
    Am I making the model, the world, or both? …. OK +Y
    Green-yellowish… no contest
    In the right column

  7. Simon Taylor’s avatar

    For no. 4, obviously I’d put them in the bottom row, and when that didn’t work I’d try the right column :).

  8. cyril crassin’s avatar

    There is a green and a yellow Chartreuse, but no way it can be orange ! It is made a few kilometers away from Grenoble 😉

  9. mvandewettering’s avatar

    1. RGB. I can’t think of a reason to consider RYB.
    2. I think of +Y as going up. It’s annoying though, since I think of pixel coordinates having +Y going down.
    3. Isn’t chartreuse a wine made in France?
    4. I’ve written it both ways. In recent years, I prefer to think of points as column vectors, which means it is most natural to place them in the last column. I believe that I’ve written raytracers with both conventions though.

  10. xskinyx’s avatar


    Question 2 could go either way though…. since alot of artwork is authored Z up. I prefer LHS, so Y up seems more sane.

  11. LRBni’s avatar

    1. A (RYB) – unless talking specifically about CG
    2. A (+Y)
    3. ? – Never heard that word to describe a colour
    4. B (right column)

  12. islet8’s avatar

    A (although i’m a game developer)

  13. itsjrich’s avatar

    1) Definitely RGB.
    2) +Y… Z is for depth, hence Z-buffering.
    3) Green-yellow… had no idea that there were other colors with that name.
    4) Right column.

  14. Reg’s avatar

    I know it’s too late but here are my answers anyway:

    * A (RGB) of course.
    * Usually A (+Y) as it’s assumed by default in DirectX/OpenGL, although I sometimes use +Z when doing outdoor terrain rendering.
    * ?? My English is not so good, sorry.
    * A because I use DirectX. And I believe it’s generally more intuitive to transform vec2 = vec1 * matrix than vec2 = matrix * vec1 😛

  15. Ivan-Assen’s avatar

    We spent our first 5 years in the industry doing 2D RTS games, so it was only natural, when starting our 3D engine, to keep “the action” in the XY plane, and make +Z “up”

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