I wanted to see where it would slow down, and by how much and thought I would displace my findings here.
Simple scene, one unreal plane (default shader), atmospheric fog, directional light, and a skysphere. Nothing crazy.
Foliage object is a single polygon strip composed of 4 quads. My alpha mask (used later) leaves the center 1/3 opaque allowing the sides to provide plenty of overdraw during the test.
There are 47,124 instances filling about 1/2 the screen.
My basic shader starts as opaque with a solid green colour. 2 sided. 0 Metalic, 0 Specular. and 1 for Roughness.
My starting speed is FPS 82-86 (seems with or without foliage this is the standard speed)
Masked mode (No Alpha)
FPS 82-86 (no change in FPS)
Opacity mask W/ Alpha
Opacity Mask W/ FULL TRANSPARENCY (
**Switch to translucent mode **(No alpha)
Opacity W/ Alpha
So my findings seem to suggest that Overdraw is certainly an issue, but translucent materials (even without an alpha) are more expensive over all at their default settings, and in fact… adding he alpha only cut about 3 FPS from the overall speed in my test. I’ll do a test with a more complicated texture next and see how much effect this seems to have.