Sunlight off mirrors in Cinema4D?

[Geof Gainer]

I'm trying to render the sun coming through a window, bouncing off a mirror, and landing on the floor. All the other incidental lighting looks perfect, but there's no trapezoidal patch of bright sunlight on the floor where one would expect it. Are there particular settings in C4D I need to set for reflected sunlight?

[Eduardo Rolon]

What I would try is placing an "Area Light" in front of the mirror at the correct angle and make sure the it is invisible to the camera.

[Geof Gainer]

I'm more inclined to think this may be a mirror problem. Or it could be a Maxon limitation, or I just don't have my settings right. See attached.

With the 'Indoor Daylight' preset, the mirror (the angled object opposite the window) seems to reflect only the sky, and not the room the mirror sits in. Same thing with the 'Indoor HDRI' preset, but the mirror looks like it's reflecting the sky above the horizon only.

My goal is to get the sunlight that's coming through the window and landing on the mirror to bounce off the mirror and hit the floor. The sunlight hitting the wall just to the right of the mirror makes the floor glow perfectly (seen best with the 'Indoor HDRI'), so maybe this is a problem with the mirror.

[Zoltan Fuchs]

Cinema 4D has two types of caustic: photon caustic and irradiance cache GI caustic.
What you want is GI Caustic. (there is no photon caustic in Physical Sky / HDRI, it needs photon emitting light).

1.Select mirror material and set parameter of "Cinerender Settings>Illumination>Generate GI strenght" to 1000 or more.
2.Switch on "Detailed Settings>Global Illumination>Details>Reflective Caustic" on Photorendering settings dialog.

It will increase render time dramatically!
Maybe you should incease the Glass/Mirror optimisation settings and try different IR cache parameters to smooth result.

[Geof Gainer]

Definitely getting closer! It's still a fuzzy reflection though, not the sharp edges you'd expect.

Mirror material "Cinerender Settings>Illumination>Generate GI strength" is set to 3000.
In photorendering settings, GI is on, and "Detailed Settings>Global Illumination>Details>Reflective Caustic" is on.

This got me pretty much to what you see now. I also tried the following, with no significant change:

Glass/Mirror optimization set to 100.
Tried pushing up various IR cache parameters.
Diffuse Depth: 3
Gamma Correction Primary/Secondary Intensity: 200/400
Tried Stochastic Sample: medium

Can I get the reflection any sharper?
(Btw, I can't open your attachment.)

[Eduardo Rolon]

Did you check the GI-> Details options?
IR should not do anything except slow things down.