How to Rock

Today I’m going to guide you through the process we took in making many of the larger 3D assets for CAVE
This asset is going to be used as a unique rock within the CAVE show. It started as a 3D model found online which was then changed to match the needs of the production.
The first step is to make sure the model has a relatively clean topology without non-manifold geometry or faces with more than 4 sides. I use Maya for my modeling so the easiest way to check for errors is by using the mesh cleanup function. This sometimes won’t solve all your problems, use the smooth mesh preview to check on the integrity of the 3D. This particular model we were using was from a Unity Asset pack.  Using mesh preview, it was evident that while the model was one object, each of its faces was separate. To fix this problem, you have to manually merge points on the mesh that are supposed to represent one vertex. Switch between normal view and the smooth mesh preview as you merge points to make sure you are doing it correctly.
The next step is UV mapping. The process is different based on the type of object you are working with but a generally good way to create a clean UV map is to use the “best plane” option. This allows you to select an object, a part of an object, or a previously defined UV, then select another 1 or more faces. A new UV map will be created for the selected object/component/UV based on the average angle of the faces selected. This allows you to create UV maps for each facet of an object while having little to no distortion. If a model already has a UV map but is not optimal, you can use the UV unfold option to make it better. Use the UV coordinate texture given in Maya to make sure none of your UVs are stretching. Try to make them uniform.
Apply a texture to the model. In this case, we are using the rockboi texture provided by Angela Yu. This is a tileable texture that we have also used for multiple other rock assets. Change the scales of the UV maps so the texture looks the way you want. Duplicate the model and use the layout option to allow Maya to fit all of the UV maps into the first coordinate space. At this point, you will use the transfer maps function. This allows you to take the UV maps from the model you duplicated (the one where you scaled the textures) and apply them to the duplicated model and have the UV maps within the first coordinate plane. This is important later for lightmapping in Unity.
Take the new texture into Photoshop and color adjust it so it looks the way you need. For this particular rock, we needed it to be red. We then applied the adjusted texture to the rock and brought it into Mudbox, a 3D painting software, as an FBX file.
Duplicate the first paint layer of the model, this layer will be used to create highlights Using the dodge tool on a low strength paint over all the edges that seem to be protruding as well as near any dark areas of the texture. We are making it look as if the edges are catching the light and giving the illusion of there being more faces on the model than there are in reality.
Once you have painted all you want, increase the radius of the brush and lower the strength more. Use the dodge tool to add some general highlights around the areas you just painted
Make a new paint layer, do not duplicate previous layers. Use the eyedropper tool to sample the darkest color on the texture – it is actually not black but a dark brown. Go through the model and use the paintbrush with a mid-strength (around 20 or 30) to continue any dark lines that need to be fixed. This will help provide more contrast with the highlights and make the texture look more continuous.
Lastly, make one more layer. go through the model and blend together the colors between the different facet of the model. This will help the texture look seamless and as if the rock it one object instead of a collection of faces.
Then I added some light shadows to different areas of the model on another layer to indicate age, depressions, and some AO.
When you enable all of the layers, you should have something like the gif below.
You then need to go through the different layers and adjust their opacity to get the rock to look the way you want. In my case, I lowered the opacity of the highlight layer to 35% and got this. The highlight is very subtle and it makes the rock look a bit more weathered and softer.
This is basically the process we used for all of the assets in the production that made use of an already made texture. Hopefully, you will be able to do something similar.

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