mr_phoenyxx opened this issue on Feb 19, 2014 · 78 posts
bagginsbill posted Wed, 19 February 2014 at 7:28 PM
Nope you don't. The key thing about IDL is that it does two important effects, pretty much at the same time.
When deciding how much light is arriving at any given point, it takes into account how much light is leaving other surfaces (near or far) that are visible from that point.
In taking into account how much light is leaving other surfaces, it recursively applies a calculation about how much is arriving at those other places and bouncing off.
People imagine that IDL is about bounced light (effect #2) but it's also about effect #1 - how much light is leaving any given surface. Bounced light is light that didn't start there, but there is light that starts there, i.e. a surface can give off light from nowhere. It is the source of the light - i.e. it is glowing.
My EnvSphere glows - it is self lit - it is the source of all the light in the scene. The amount that it glows, at every point, is defined by the HDRI you attach to it.
So - the EnvSphere is set up to not bounce any light at all - while simultaneously emitting exactly how much light is recorded in the HDRI. The result is that it reproduces the lighting of the world around our scene, while not actually participating in it. If you were to load a black image onto it, you would see it as black and no amount of Poser lights (point, spot, or whatever) would influence how much light leaves its surface.
When you build a shader, you are deciding two things:
How much light originates from that surface (self-lit, glowing)
What % of light bounces from that surface.
I have the EnvSphere set up to emit the image, and bounce nothing.
Ordinary objects are set up to emit nothing, and bounce a fraction of the light that arrives. These ordinary objects are still adding bounced light to the equation, but they are not adding light. They only contribute light that arrived from elsewhere.
Renderosity forum reply notifications are wonky. If I read a follow-up in a thread, but I don't myself reply, then notifications no longer happen AT ALL on that thread. So if I seem to be ignoring a question, that's why. (Updated September 23, 2019)