Why would triangles compute (render) faster than quads?

My guess is because they're inherently planar.  Every triangle is flat, while a quad can be distorted.

So even though we overlay things like curvatures and surface normals and stuff to make our geomerty appear smooth and curvy, the flat nature of triangles might remove one step in the computational process.

It's just a guess.  (I used to be very invovled with Finite Element Analysis, so I have some understanding of mapping, though for a different purpose.  But as I said, this is really just a knee-jerk reactionary guess.)

ADDED...

I re-read sw00000p's post, where he said, "Quads are converted into Tri's. (an Extra Processing Step)."  It's not exactly proof, but it does support my theory.

ADDED MORE...

I wonder how much effort goes into the quad-to-tri conversion.

Draw a 4-sided object that is nearly triangular.  Something like a triangle, but with a slight buldge/bend on one of the sides.

If you draw a line between opposite points, in one case you get two nice triangles.  But if you go the other direction, you'll get one nice triangle and one that's just a sliver of a triangle.  Badly formed shapes like that sort of mess up the math, especially in computational anlaysis.  You end up nearly dividing by zero and stuff like that.

In fact, what if you drew a real triangle, but just added a fourth point in the middle of one of the sides?  Repeat the excercise in the previous paragraph.  You end of with a nice triangle and, essentially, a line.  Ewww.

So I wonder if the quad-to-tri conversion routine evaluates each quad and determines the best way to subdivide it into triangles?  If so, you add more work, reducing performance.

---

iClone 7... Character Creator... Substance Designer/Painter... Blender... Audacity...
Desktop (homebuilt) - Windows 10, Ryzen 9 3900x CPU, GTX 1080 GPU (8GB), 32GB RAM, Asus X570 Pro motherboard, 2TB SSD, terabytes of disk space, dual  monitors.
Laptop - Windows 10, MSI GS63VR STEALTH-252, 16GB RAM, GTX 1060 (6GB), 256GB SSD and 1TB HDD

I had to look that one up too. Found that same article, which lays it out pretty well.

I had always wondered if any game engines actually used quads. I knew they are really advantageous for modelling. But I did not know that tri's were faster for rendering before reading that.

My bad, for not doing my homework before posting on this one!

Good info anyway, though.

Hello ,

An old thread about tri/quad with Mike .

https://forum.reallusion.com/Topic117074-14-1.aspx?Highlight=quad

CGTRADER

Also, don't forget optimization with triangle strips:

(from wikipedia)

"A triangle strip is a series of connected triangles, sharing vertices, allowing for more efficient memory usage for computer graphics. They are more efficient than triangle lists without indexing, but usually equally fast or slower than indexed triangle lists.[1][2] The primary reason to use triangle strips is to reduce the amount of data needed to create a series of triangles. The number of vertices stored in memory is reduced from 3N to N+2, where N is the number of triangles to be drawn. This allows for less use of disk space, as well as making them faster to load into RAM."

Once the first triangle is constructed, each triangle afterward can be made by sending a single vertex through the pipe.