Refactor PShapeOpenGL

[codeanticode]

So all the VBO code goes a into a Cache object, like Texture does for PImage.

[codeanticode]

@benfry I will start working on this after 2.1 final is out, feel free to add any notes/comments/suggestions you think are relevant.

[codeanticode]

This refactoring could also be an opportunity to reduce the memory footprint of PShapeOpenGL:

http://forum.processing.org/two/discussion/1071/point-clouds-in-processing-2-1-with-opengl#Item_2

[kosowski]

I think it would be interesting to have some kind of basic PShape, something closer to GlGraphics GlModel, where the flexibility of PShape is traded for GlModel’s performance.

I would like to move some ongoing projects to Processing 2, but without lowering the number of vertices used. Dealing with the arrays in order to modify vertex properties is worth the performance difference for me.

[codeanticode]

Something else to keep in mind, not necessarily for 3.x but maybe for a later time, is the support of generic vertex attributes. Right now the vertex attributes are hard-coded in the renderer to be position, color, normal, texture coordinates, ambient, specular and emissive colors, and shininess, as a legacy of the fixed-function pipeline in 1.x. In the programmable pipeline that now Processing uses, one can assign arbitrary parameters to each vertex, i.e. instead of position, or color, or any of the others we support, a shader can take its own variables, like, say, "fuzziness".

So eventually we'd implement this something like:

sh = createShape();
sh.beginShape();

sh.fill(203, 100, 44);
sh.attrib("fuzziness", 0.5);
sh.vertex(40, 30, 20);

sh.fill(200, 141, 100);
sh.attrib("fuzziness", 0.4);
sh.vertex(30, 20 30);

// .. and so on

sh.endShape(); 

Implemented in #2963

[codeanticode]

As part of this, I will combine VertexBuffer with PGraphicsOpenGL.VertexAttribute.

[benfry]

FWIW, I think this is post-3.0, unless there's something serious that's being fixed here. It's not pretty at the moment, but it's not like people are raiding the castle demanding a cleaner internal design for PShapeOpenGL.