Per-face colors in plot_trisurf

[deeplycloudy]

The docs for pylab.plot_trisurf state that triangles is of shape (N,3) and that color should also be of shape (N, 3), implying that the colors will apply to the triangle faces, not the vertices.

However, the observed behavior (on version 0.4.0a2 from PyPI) is to color the vertices.

colors = np.ones((4,3))*.3
colors[0, 2] = 1.0
colors[3, 2] = 1.0
plot_trisurf([0, 0, 3., 3.], [0, 4., 0, 4.], [1, 0., 0, 1.], 
                triangles=[[0, 2, 3], [0, 3, 1]], color=colors)

If the above behavior is as intended? If so, is there another way to set the triangle face color directly?

[maartenbreddels]

Hi Eric,

I've modified the docs, it is only possible to specify per vertex properties, and these will be interpolated (at least that I know of, for WebGL).
A workaround is thus to duplicate the vertices:

ipv.figure()
colors = np.ones((6,3))*.3
colors[:3, 2] = 1.0
colors[3:, 0] = 1.0
x = [0, 3., 3., 0, 0., 3.]
y = [0, 0., 4., 0, 4., 4.]
z = [1, 0., 1., 1, 0., 1.]
ipv.plot_trisurf(x, y, z, 
                triangles=[[0, 1, 2], [3, 5, 4]], color=colors)
ipv.show()

Maybe it's an idea to have face_colors supported, that would do this automatically.
I've also updated the documentation for this. Let me know if this solves it.

cheers,

Maarten

[deeplycloudy]

Hi Maarten,

Yes, the docs update will be helpful for others, and for now I can duplicate the vertices as you suggest. I'm doing some tests with fairly large meshes — O(10^6) vertices from a research weather radar — so there is some downside to duplicating, but I should still be ok.

In the future, +1 for face_colors support!

Thanks,
Eric

[deeplycloudy]

Another thought: I was using the face_colors support in vispy in some earlier tests. Not sure if they also auto-duplicated vertices, or if they used some lower-level GL support for face colors.

[maartenbreddels]

Thanks, I'll keep this open and dive into it later, maybe it is possible more efficiently.

[maartenbreddels]

I think this can be done at the kernel side first, I guess face_colors and triangle_colors arguments to plot_* would need to sort out the duplication of vertices manually.