Thursday, October 9, 2014

Light 'em up

It's lighting week.

First off, Blender's new Cycles render engine is pretty spiffy.  Path tracing just makes lighting look so nice.  Plus it's more or less interactive, as it can do a very low-res pass fairly quickly as you're moving the camera around.

Even better, Blender 2.7 added texture baking, so all of that yummy lighting goodness can be used to make lightmaps and such.

So far, the pipeline to convert a Blender shader graph into a GPU vertex/fragment shader has worked really well.  Obviously there are some limitations - path tracing and triangle rasterization are just completely different ways of doing things - but I can build up a complex set of materials and more or less get the same thing in the game.

Here's a ship in Blender:


And in-engine:



Not exactly the same, but similar.  It looks a little washed out, some of that is the bloom effect not present in the render.

This is using lighting based on the skybox - spherical harmonics for diffuse, plus a biased mip map sample to get a blurred / rough specular reflection.  It looks pretty nice in motion.  The emissive materials help as well.

Self-illumination and ambient occlusion maps would help a bit.  It may also be worth generating point/directional lights for hot spots in the skybox to give some added definition to the normal maps.

Some day we'll be doing real-time path tracing (or something similar), and it's going to be awesome.  :)

Points of note:
  • Using the shader instruction texCUBEbias(...) to  choose a "blurred" mip level was not working properly.  The documentation on this instruction is pretty vague, but I kept getting really strange results.  texCUBElod(...) seems to do what I want.
  • The auto-generated mip maps for the cube map definitely have seams at lower resolutions.  This seems a little tricky to fix, I may just live with it for now.
  • Using D3DXSHProjectCubeMap(...) to generate the spherical harmonic coefficients was not working as expected - it looks like x and y are both negated?  Anyway, negating coefficients where the sign differences don't cancel out gives light coming from the right direction.
That's all for now, have a great week!

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