Maybe the first direction to take would be the use of shaders and slabs(jitter tutorials 41-43) so you can free your CPU. Another interesting direction would be to explore cv.jit library.
Are you familiar with the GL jitter objects?, if you want to draw lines or any other shapes you can use jit.gl.sketch where you can send ‘raw’ gl commands, for instance the glvertex or the lineto, etc. you can control the width of the line with the line_width message or the linewidth command. For color you have the glcolor.
Shapes can be drawn using the glbegin / glend command and a series of vertices.