Is it true that rendering a high amount of textured "N-Gons" without transparency is faster than the calculation of textured "Quads" with transparency?
I guess that depends on the amount of Vertices/ triangles the N-Gon exists of (for rendering everything is being triangulated).
If the N-Gon has 4 Vertices, than it will of course be faster to render than a Quad with transparency ;)
If the N-Gon consists of 1 million Vertices, than that will render a lot slower than a Quad with transparency.
There must therefore be an amount of Verts, which is a turning point, where it switches which one is faster.
It might also depend on the amount of transparent bounces...
Yes, that is perfectly true, but again, there will be an amount of vertices where alpha textured Quads will render faster.
But generally with leaves you will not pass that turning point and this method gives the possibility for nice deformations to the leaves.
Transparency can be expensive! Instancing makes no difference with that, but instancing does make a big difference with calculating geometry. It's why I chose to cut out the leaf shape here instead of using the ivy generator's quads. If it wasn't instanced and this was for a game engine rather than a path-tracer then I might have left them as a plane.