Change texture based on angle

[krumpytail]

I want to change the texture on an object based on the angle of the camera as opposed to the lights. So if I have a light and a camera pointing at an object and the viewing angle is less than lets say 15

[failure]

What do you need it for?

[drblacksnake]

Sounds like
samplerInfo.facingRatio -> condition -> blendColors.blender -> shader.color.

but there would be cases, when part of an object is in 15deg range, and part is out - so You'll gona face object with two textures.

thus instead of samplerInfo You can use some maths, to just calculate angle between camera and locator parented under particular object and this would be faster.

[krumpytail]

For glowing eyes, the tapetum lucidum, for several animals in a dark scene.

[joojaa]

Well in that case you are a bit off its not a texture based on angle but rathera atexture based on light reflection angle.

But yeah you can use a facinforward connected to a armp to achieve faked effect like this. offourse it realy would need a lightinfo to match up with this but....

[failure]

Problem is a bit ill defined since "angle between light and camera" makes not much sense.
Anyway. if I got I right what you want is basically a fake fresnel reflection of the light source. driving the blend ratio betwen two textures.

Well that's what common shaders like phong and blinn already claculate as a part of their shading equation. And it goes under name of "specular highlight". Minus fresnel part of course. So, by exploiting specular calculation you can build the shader without any vector math nodes.

Basically, make a black phong with broad and strong specular highlight. Multiply its output with the facing ratio ( output of samplerInfo ) and connect the result to "blender" attribute of a blendColors node. Of course you might want to remap the facing ratio thru a ramp for more control. The rest is obvious; fill in two texturers as color inputs of the blendColors node and connect it's output to the final material.

But honestly this is too much work with too little control in return since now you'll need to tweak the whole scene lighting and camera position just to get the glowing eyes. Wouldn't it be much easier to just keyframe the blending ratio as needed? Or even beter - render the eyes' alpha and do it all in post.

[krumpytail]

Where's the fun in keyframing it. I'll give it a go with what you've said and see how that works. I might even try it in post.

[joojaa]

Yes getting the light there n position is a pain in the butt. BUT you can retrieve the angle by getting the light position with lightinfo point position with sampler info and then cal cthe camera position in to that and thake the cross product of this. BUt thei basicaly yealds lambert shading. So you can connect out color of a withe lambert to a ramp instead.

[failure]

"Where's the fun in keyframing it."

"Fun" is in having more control. For example - you have a shot of several animals with glowing eyes and client has a very specific idea on when particular pair of eyes need to sparkle. Nice, no problem - we'll have fun adjusting the lights. But client then changes its "idea" to totaly different timing. Nice, some more light moving fun. Next day the client wants to try something else with glow timing. More fun. More fun. More fun. etc.

If it's doable in post - there's no reason not to do it in post.

[krumpytail]

I see your point. Less work is more fun. Lets try it in post.