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There are two lighting preview modes in hammer in the new SDK, "lighting
preview" and "ray traced lighting preview".
Both require a high end dx9 GPU supporting floating point textures and
render targets and will use a fair amount of texture memory if invoked.
The basic lighting preview mode is 100% gpu-based, and renders pretty
much as fast as any other hammer rendering mode. It approximates the
effects of the most important (i.e. closest to the camera and brightest)
lights from the map. This mode has the following limitations:
- no shadows.
- no sky ambient
- no direct light from the sun. While this could be supported, at the
moment it is turned off because of the no shadows limitation. It was
thought by me to not be especially useful because you'd see the full
effect of the sun everywhere, even inside a dark tunnel. Internal
feedback has been given that it would probably be useful as a toggle
able option.
- in order to slightly simulate bounced light, every light leaks a
little light into the environment. So, a spot will cast a little light
outside of its cone.
- only the 10 "most important" lights are rendered. By
enabling/disabling lights, you have some control over this.
What it's good for:
Adjusting light angles, positions, spot light cone parameters,
colors, and falloff, with feedback about what objects the light will
hit.
The ray-traced lighting preview is a superset of the first mode. When
this mode is selected, the window will act as in the first mode, but a
separate window will come up and asynchronously update.
This window is independent of the main hammer window, with the intent
being that users will drag it onto the 2nd monitor if they have one.
This mode works by capturing the albedo, position and surface normal of
every pixel of the GPU-rendered scene. It then, on another thread,
applies all lights to this data, doing SIMD ray tracing for shadowing
and lighting calculations. It uses progressive refinement to render the
light from each of the light sources in the map at successively higher
resolutions until the image converges on a high quality one. It attempts
to figure out which lights contribute the most to the current view and
render those first. This mode _does_ render sky ambient and sunlight and
shadows, but not bounced light.
Note that in order to not slow down hammer, the thread that does this
rendering runs at a low priority. As a result, it will work way better
on multi-core systems.
I hope map makers find this functionality useful. It's a work in
progress and we have a lot of internal feedback about where to take it
and how to further improve the map builder's workflow.
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