Hey, it's almost the same! Maybe we can assimilate it even more? We can, because apparently the step value of our mr custom bump needs to be 10 times lower and it's factor 10 times higher to compensate the differences - this is the adjusted mr custom bump:
Except a few pixels, the result is exactly the same as with a bump2d. Exciting, isnt it?!
Well... You probably ask yourself what the other available bump node, the mib_pass through_bump_map is good for. It has the same effect, it is only connected differently to the shading network. Here's a snapshot of what I mean:
Ugh. What's that blendColors node doin there? Well, I guess the mentalray developers simply had a good idea to pass a bump vector through a shading network if you don't have a Bump Mapping slot around, as with all mr custom shaders like the Cook-Torrance or DGS for example. The blendColors color1 is the mib_passthrough_bump_map, and color2 is the texture (a plain gray color in our case). It's Blender value is very low at 0.001, just as low to be non-zero. It's a trick of course. The result is the very same though (with adjusted step settings etc.):
So. What are the reasons to use custom mr bump shaders? If you ask me, I dont see any. The bump2d has, with all filters off and mipmap activated, the exact same output. As long as you dont use mr custom shaders [i]plus[/i] as long as you dont have no bumpCombiner or bump passthrough around (*), it's wasted time to build this networks (probably not in [i]every[/i] case of course).
In reverse, the bump2d has some big bonus like the bumpFilter and the ability to use texture filters (quadratic etc.) to reduce texture artifacts, and all the other benefits that come with the regular maya file and texture nodes.
NB: This is a rough comparison between the two methods to get mentalray bumping. It may, of course, not apply to [i]all[/i] possible situations. And [i]do[/i] try this at home!
You could set your surface's normal (bump it) by passing any shader through a plain standard maya lambert's incandescence, set the lambert's color to black, it's diffuse value to 0.0, and plug a regular bump2d into the Bump Mapping slot as you would do as usual. The shader in the incandescence slot inherits the altered surface normal from it's parent, the maya lambert.
