Can a shader be used to not render parts of a skinned mesh?

Assu$$anonymous$$g your shaders write to/test the depth buffer (i.e. ZWrite On and ZTest LEqual, which are default for any non-transparent shaders) then the behaviour you describe already happens automatically - when a candidate pixel is about to be rendered, if there is already a pixel in the depth buffer that is closer to the camera then the candidate will be culled. Unless I've misunderstood your question, in which case perhaps a screenshot would help of what you're trying to describe..

Ok I've added a screenshot. What I need is for the part of the small sphere that is inside the large sphere to not be rendered. This is similar to a boolean operation except the mesh itself would not be changed, just the intersecting polygons would not be rendered. Is this more clear?

To the best of my knowledge, no. You cannot use a shader for the purpose you described. A shader is a program that ultimately calculates the color of a pixel of an object it is assigned to. It works on the object's level (and various parts of the shader program work on vertex level and pixel level) and cannot have any knowledge of any nearby objects of their surface properties.

Like tanoshimi said, the depth check happens automatically anyway, but if the background object gets rendered first, and then foreground object draws over it, then yeah you're dealing with "overdraw", essentially you're wasting time by drawing the background object.

$$anonymous$$ost 3D Engines, Unity included, do their best to overcome this problem by drawing closest objects first. But long story short, no there really isn't anything you can do about it in your particular example.

In fact you'd probably spend more CPU or GPU time figuring out what's occluded/clipped and discarding those surfaces, then simply rendering everything without such conditions.

If your currently struggling with performance, you're looking at the wrong solutions. Reduce the number of objects on scene, or use simpler shaders to draw them, use static occluders and Occlusion bake as much as possible. If you're using multiple dynamic lights, use deferred renderer. If not, use forward renderer and bake all non-dynamic lights in. If you have any custom written shaders, give them a once-over against known shader optimization guides to make sure they're not running slower than they should.

@Eudaimonium , ok how about if ins$$anonymous$$d of trying to figure out exactly what is intersecting what, I only use a texture. So for example all of the black parts of the texture would not get rendered but the white parts would get rendered. This is similar to an alpha texture, but it would not make the surface only transparent, it would not render those polygons.