Programming my own triangle rasterization for OpenGL?

Question

I am trying to render rounded triangles to increase performance. To illustrate what I mean, see the picture below:

I tried in the CPU, now is there a way to move this algorithm somehow to the GPU? I can change the method's code that calls the fragment shader?

By the way if I can do it, then what programming language I need to re-make it to?

I am using an OpenGL 2.1 GPU with just 20GB-30GB memory bandwidth.

Answer 1

I'm not sure exactly what you're up to, but it seems a bit dubious. You can actually end up hurting performance trying to do some of these custom calculations in a shader to render a circle or ellipse.

Modern GPU hardware can push billions of triangles a second. You're probably splitting hairs here.

In any case, if you want to 'fake' the geometry, this may be of interest to you: https://alfonse.bitbucket.io/oldtut/Illumination/Tutorial%2013.html

Answer 2

Read the paper Resolution Independent Curve Rendering using Programmable Graphics Hardware by Charles Loop and Jim Blinn.

Short version: assuming you have an efficient inside/outside test for your curve, render the enclosing hull shape as triangle(s), use a fragment shader to discard the pixels outside the curve.

Second the concern by Aeluned that transferring the algorithm to the GPU won't automatically make it faster.

Answer 3

1. Well on OpenGL 2.1 you do not have geometry shaders (3.2+) so you can forget about GPU.
2. You can not improve rasterizing performance of convex shapes by your curved triangles
   • complexity of rasterization of any convex polygon is the same as any triangle of the same area
   • the difference is only in:
   • number of passing vertexes
     • memory transfer
     • with geometry shader this will be better with your triangles usage
   • number of boundary lines
     • boundary lines rasterization for filling
     • will be worse with your triangles usage
     • (need to join more triangles instead of single shape polygon)

So its not a good idea to implement this for better performance in your case.

The only thing i can think of to use this for is to ease up manual generation of shapes.

In that case just write a function glRoundedTriangle(....)

• which generate the correct vertexes,colors,normals,texture coordinates from given input parameters.

how it would looked like is unknown because you did not specify the rounded triangle geometry/shape and/or input parameters (for example 3 points + 3 signed curve radiuses ?)

To improve performance in OpenGL use VBO/VAO