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Advanced Baking - Baking Next-Gen lighting with Turtle

By Illuminate Labs
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Date Added: 9th December 2009
Software used:
Maya, Misc

The baked normal map contains the geometrical details from the highresolution Source Surfaces, stored as image data in an ordinary RGB image.

The sampling of the normal map is completely controlled by the Sampling roll-out in the Render tab of the Turtle Render Settings. You can also select regions in the Render View to re-render, if some areas need higher sampling.

Take a peek at the Outputs roll-out in the Surface Transfer tab again. You can now bake down almost anything with Turtle 4. You can bake down any custom shader and even control Turtle through LUA scripting, so baking normal maps is just the start of what Turtle 4 can do!

You can visualize the normal map inside Maya by connecting an ilrHwBakeVisualizer shader, but it's often easier to check Model View Hardware Visualization in the Output File roll-out of the Surface Transfer tab. A hardware shader will be connected to your object after rendering. Any software shader on the object will remain untouched.

Check Model View Hardware Visualization, and render out a new texture. Remember to enable Hardware Texturing in the Shading menu of your Maya viewport, and switch off the lights inside the hangar by picking Use Default Lighting in the Lighting menu of the viewport.

1299_tid_image05.jpg
The bump maps on the high-res geometry do not contribute to the normal map by default, so check Include Bump Maps in the Outputs and bake out a normal map with bump maps as well. Rename the old map before you render and we'll make use of both maps later.

Parallax Mapping

We can check out one more really simple trick before we proceed with Turtle 4's new baking features. Uncheck the Include Bump Maps attribute to get the simple flat shading in the normal maps. Check the Displacement in Alpha Channel instead, and Turtle will now render out a black-and-white height map into the alpha channel of the normal map. If you still have the Model View Hardware Visualization checked, Turtle will automatically connect the map for you and switch on the Height Map in the hardware shader, so go ahead and hit render. Remember that both Source Surfaces and Target Surfaces need to be visible for a Surface Transfer!

The default values for the height map should be a bit too high for this scene, so dig your way down to the hardware shader for the object and set the Scale in the Height Map roll-out to 0.025. Go ahead and check the base mesh from different angles. Notice how there is a better illusion of depth now? The pixelshader on the object actually ray-traces the object locally, which creates an approximate displacement effect on the surface.

1299_tid_image06.jpg 1299_tid_image07.jpg

A useful trick for making the effect of parallax mapping slightly more pronounced is lighting the surface from different directions with slightly different colors. Also notice the shading artifacts along the true edges of the low-res mesh. As the effect is only local to the surface, the details which seem to be displaced out from the surface will still be cut-off at the edge of the mesh. You should probably model those protruding blocks on the walls with geometry. It's a good thing to keep an eye out for any problem areas and try to plan ahead. If you use parallax mapping wisely, you can make your work really shine.

Texture Baking

We're going to bake out a Radiosity Normal Map, a technique that was extensively used in Half-Life 2. In a Radiosity Normal Map (RNM), indirect lighting is baked down for every point as an RGB color for three different directions. This makes it possible to interpolate the specific indirect lighting by weighting among the three color samples appropriately, depending on the normal of the surface. This will make it possible to swap normal maps on our hangar base, and still use the same RNM for indirect lighting look-up, or direct illumination for high detail light maps.

All you need to bake down an RNM is the low-res geometry receiving lighting, so the option to bake Radiosity Normal Maps only exists in the Texture Bake tool. As you might recall, Texture Bake just samples down any property you want into a texture map which you can then reapply on the source surface of the baking.

Open the Display Layer Editor, and hide the hiResBase layer; we'll not need it again since we baked out normal maps. Under the Render tab, change RenderType to Texture Bake. As the RNM will only capture indirect lighting, we'll boost the lighting a bit so the effect is more pronounced. Create a new point light with intensity 500, and cubic Decay Rate. Set the color to bright green, and position the light at the back of the hangar towards one of the corners. Neat Area 51 lighting, huh?

Switch to the Texture Bake tab in the Render Settings, the default Bake Layer is OK, since the low-res geometry should already have been added to it when we baked the normal maps. Open up the Outputs roll-out and make sure only Radiosity Normal Map is checked. You might be tempted to throw in some final gathering and such, but Radiosity Normal Mapping already does a sort of final gather for indirect illumination. You'll get a kind of doubled illumination, but it won't be a healthy Radiosity Normal Map. You can even use RNMs together with photon mapping, but you have to use a Dynamic Photon Map, which stores photons coming from every possible direction in the scene. Everything should now be prepped for an RNM texture bake, so go ahead and hit render.

1299_tid_image08.jpg
You will only see one image in the Render View, but if you check the output directory you will actually have three files, each one representing lighting for one of the RNM basis vectors.

The ilrHwBakeVisualizer shader has built-in support for RNM maps, so you can either plug them in there, or simply check Model View Hardware Visualization in the Output File roll-out of the Texture Bake tab before you render.

1299_tid_image09.jpg

If you enabled visualization when we baked the normal maps, you might already have a normal map visible, otherwise you can locate the visualizer shader in the Hardware Shader roll-out of the active material. Remember to enable Normal Map in the Hardware Shader Features if it's not already enabled. Go ahead and try the normal maps we baked earlier together with the RNM. Turn off all lights and hide the hiResScene Display Layer to see a more pronounced effect. No matter which normal map you apply, the indirect lighting will update to match. Such is the magic of RNMs!

1299_tid_image10.jpg
If the RNM is used to bake Dynamic Illumination, you will actually get a highdetail light map. Even though the RNM might be very low in actual pixel dimensions, it will still adapt to the normal map and shade accordingly, which is a trick used extensively in Unreal Engine 3 and next-gen games.





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