Apply clipping planes to only specific area of object

[PavelBoytchev]

@Panda

My current solution is to split the model into two separate meshes so that I can apply the clipping planes in isolation. This works, although since my models are slightly transparent, there is a visual bug where the other portion of the model cannot be seen through the inside of the other. Messing with the rendering order between the two meshes only seems to flip which side this happens on

I tried slightly different approach and there is no visible problem where the two halves are attached, although there are transparency issues in other parts of the shape, but they are not related to the cutting and stitching. Here is the result (left is stitched object, middle and right are both halves):

https://codepen.io/boytchev/full/ExeoeOJ

I do the following:

• Cutting is done by an additional horizontal cutting plane through the middle of the object. So, there are two identical obejcts: one shows only its top half, the other – its bottom.
• To resolve transparency at the point of object cutting, each of the two identical objects are additionally split into two – with FrontSides and BackSides.
• Overall I have 4 identical objects – top-front, top-back, bottom-front, bottom-back. Render order ensures the back objects are drawn before the front objects.
• Obviously there are no caps.