Basic approach to pupil constriction/dilation of eye model in OpenGL

3
votes

I'm new to OpenGL-ES and looking for the best approach for creating a realistic model of an eye whose pupil can dilate and constrict so I have a plan in mind while running through tutorials.

  1. I've made a mesh in blender that is basically a sphere with a hole (the 'pole' or central vertex is removed and a couple surrounding circle edges).

  2. I plan to add an iris texture directly to the sphere's polys surrounding the hole.

  3. To change pupil size, do I just need a function to reposition the vertices of the hole so the hole dilates or contracts?

  4. I'm going to use OpenGL within an Objective-C app. I have Jeff Lamarche's Objective C export script. Is it standard to export only the mesh from blender, and add textures in code later in xcode? Or is it easier/better to setup the textures on the meshes in blender first and export the more finished product's data to xcode?

1
animationopengl-esblender3d-modelling

1 Answers

1
votes

Your question is a bit old, so I'm not sure how much progress you've made, but as I've been climbing up the learning curve myself I thought I'd take a shot at answering.

If you want to animate the individual vertices of your model, I believe the method you'll want is Vertex Skinning. I can't speak much on that front as I haven't yet had reason to experiment with it, although it's a technique only available in OpenGL ES 2.0. (Which is probably where you want to start anyway, the increased flexibility over 1.1 is more than worth any additional incline to the learning curve.)

The answer to your texturing question is somewhat mixed. You'll need to actually apply the texture in OpenGL. But what Blender can do for you is determine the texture coordinates. Each vertex of your mesh will have a texture coordinate associated with it. The texture coordinate will be X, Y coordinates which map to a location on the texture image. The coordinates are in a range from 0.0 to 1.0 -- so, since your image texture is a rectangle, the texture coordinate {0, 0} maps to the bottom left corner; {1 , 1} maps to the top right corner; {0.5, 0.5} maps to the exact center of the image.

So in blender, you'd want to go ahead and texture the object with UV mappings. When you export, although your exported mesh won't contain any of the image content, it will retain the texture coordinates which map to your image content. This will allow you to apply the texture in OpenGL so that the texture is applied the same way it appeared in blender.

I've personally had some trouble getting Jeff Lamarche's script to spit out the texture coordinates, as Blender api seems to change significantly with each release. I've had more success with an .obj converter. So I've been exporting from blender to .obj, and using a command line tool to go from .obj to a C header file.

If you encounter similar problems with Lamarche's script, this post might help solve it: http://38leinad.wordpress.com/2012/05/29/blender-2-6-exporting-uv-texture-coordinates/

And this is a good resource for a .obj to .h script: http://heikobehrens.net/2009/08/27/obj2opengl/