Game Development Reference
In-Depth Information
Rendering multiple cubemaps and image proxies. In order to render multiple cube-
maps correctly, we should render each cubemap and its linked image proxy sep-
arately and then blend the result. This is because of the reflection plane, the
sorting order and the blending mode of the image proxies. This has both a mem-
ory and a computational cost. As a performance optimization, we chose to first
render all cubemaps sorted by increasing blend weight with additive blending,
then render all sorted image proxies. This can cause trouble when mixing cube-
maps with different reflection planes but we let artists manage this case. Other
artifacts are less noticeable.
Extra care needs to be taken for character image proxies as these are dynami-
cally linked to the cubemaps. In the blending case, they must be linked to all the
gathered cubemaps in order to be fully visible (the sum of their blending weights
will equal 100%). We render them in each cubemap rather than at the end to
get smoother transitions when a cubemap with a different reflection plane comes
into the mix.
Similarly to character proxies, other image proxies may be shared by multiple
cubemaps. If the image proxy uses interpolative blending, this could result in a
final image intensity that is lower than expected because of repeated interpolation.
This can be fixed in the shader by tweaking the alpha value according to the
blending weight.
Image proxy best practices with local IBL. Our local IBL approach provides seam-
less transitions between lighting environments represented by cubemaps. A sim-
ple example of a corridor environment has been presented in our SIGGRAPH
talk. This still applies to our planar reflection. We set up three cubemaps in
the corridor with overlapping influence regions and identical geometry proxies.
For clarity, only the geometry proxies (the box volumes in red, green, and blue)
are shown, with a small scale so that they are all visible. This setup and our
planar reflection technique provide detailed reflections and smooth transitions
( Figure 1.9 ) . There is a video on the CD accompanying this article showing the
result when the camera moves.
Image proxies are of great help in more complex cases. Again, artists must
be creative, and we help by presenting some best practices. Figure 1.9 s hows the
setup of geometry proxies and screenshots of typical usage (refer to the video for
better visualization). Purple lines are image proxies; red, green and blue boxes
are geometry proxies of cubemaps:
1. Corner corridor: The set of geometry proxies include a concave volume.
Artists use image proxies to hide the artifacts.
The image proxies are
captures of the walls.
2. Two successive rooms, separated by an opening door: The geometry proxies
overlap and include the two rooms. The image proxies are captures of the
separating walls. Walls should not be included in the cubemap generation.
 
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