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Determining material/properties of a vertex or triangle on a mesh
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Posts: 2


Sun, Jan 5 2014

Hi There!

Thanks for the framework. It's been working great thus far. I've been looking into re-creating the touch detection that a previous user had created a project for and have it working based on preliminary tests (I'll post to github for sharing soon). Now I'm at the point where I'd like to see what kind of properties I can glean from knowing the particular point in the mesh I have touched.

This is really a general question but given the vertices/triangle on a mesh (or it's tex coords...etc.) how could I determine specific properties of the mesh at that point? For example: If I had a cube and on two of the faces of the cube I applied a specific material while on the other 4 was a different material could I determine the material of the face I was touching? As a newbie to opengl/ninevehGL I'd like to be able to touch a mesh at a certain point and have 'properties' I could derive from touching that position. Is there a smarter way to do this?

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Posts: 571


Sat, Jan 11 2014

In response to: @jjsidhu23

Hello buddy,

To do that you'll enter in the NGLSurface world. It's not hard to understand, but it's hard to use, because you need to know your mesh, I mean, the vertices and structure of your mesh, because you'll work directly with the vertices' indices.

The concept is very simple. Create a NGLSurfaceMulti, inside it put how many NGLSurface(s) you want to divide your mesh. Each surface will automatically receive a unique identifier if you do not this explicitly when creating each NGLSuface.

Each NGLSurface has a start and length index. Which represent the starting vertex's index and the length until the end of this current surface.

This is the hardest part. After that all that you need is similarly create a NGLMaterialMulti or NGLShadersMulti. Each identifier inside these "multi" kinds will match exactly with the index you've set on your NGLSurfaceMulti.

The concept is the same as surfaces in 3D modeling softwares like 3DS Max and Maya. Besides you can notice that all the imported meshes already come with this structure. So if you want to get references, just use NSLog on the imported mesh's material, shader and surface.

Hope this helps.
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