It has the right methods,

but claims to not support it

There probably needs to be some git-forensics to sort the history out here.

The problem is with the SVG backend. Its giving correct output with cario backend. Here's the mplcairo implementation to generate SVG file and it seems to work.

import numpy as np
import matplotlib as mpl
mpl.use("module://mplcairo.qt")
import matplotlib.pyplot as plt
import matplotlib.tri as mtri 
from cairocffi import *
#%matplotlib notebook
#plt.switch_backend('mplcairo')
print(mpl.get_backend())
%config InlineBackend.figure_format = 'svg'
# Mesh
N = 10
x, y = np.linspace(0, 1, N), np.linspace(0, 1, N)
X, Y = np.meshgrid(x, y)

# simple function over the mesh
Z = X**2 + Y**2

# triangulate
tri = mtri.Triangulation(X.ravel(), Y.ravel())
plt.Figure()
# plot
fig, ax = plt.subplots(1, 2)


# default
ax = fig.add_subplot(1, 2, 1)
ax.tripcolor(tri, Z.ravel(), 
                   cmap=plt.cm.coolwarm)
ax.set_title('default')
ax.axis('equal')


# gouraud
ax = fig.add_subplot(1, 2, 2)
ax.tripcolor(tri, Z.ravel(), 
                   cmap=plt.cm.coolwarm, 
                   shading='gouraud')
ax.set_title('gouraud')
ax.axis('equal')
plt.savefig('outputmplqt.svg')
#plt.savefig('outputmplqt.png')
plt.show()

@avinashmnit30 Is a diff of the two svg files understandable?

@tacaswell "Cario backend" is using PNG image within <image> element of the SVG. So, it's not actually generating Gouraud-triangles in SVG.
Also, the "SVG backend" implementation of Gouraud triangles is incorrect. Its mentioned that it is following http://www.svgopen.org/2005/papers/Converting3DFaceToSVG/index.html paper. But the implementation is incorrect.

Example:

Code for reproduction: https://matplotlib.org/2.0.1/examples/pylab_examples/quadmesh_demo.html

SVG Backend Output:

Using correct implementation:

Is this still an open issue given #11378?

This is the output on current master.

The non-masked version is now correct. However, there is a difference for triangles that are adjacent to the masked area: Our SVG implementation does not add transparency to these triangles. Probably it should, but I'm not an expert in these things.

fwiw cairo (and thus mplcairo) renders this "correctly" as SVG, but does so by rasterizing the entire mesh.

The current version of svg_backend doesn't work. I think rasterizing the mesh is the only way to achieve Gouraud shading in SVG files at this moment. Because even if triangles get right Gouraud colors, the anti-aliasing issue (#5694) between two adjacent patches would out make the output useless.

Something like this:

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I think this is still valid.

I recently had an issue with svg format and 'gouraud' shading.
Thanks for the tip to add 'rasterized=True' to the tripcolor() function.

This issue has been marked "inactive" because it has been 365 days since the last comment. If this issue is still present in recent Matplotlib releases, or the feature request is still wanted, please leave a comment and this label will be removed. If there are no updates in another 30 days, this issue will be automatically closed, but you are free to re-open or create a new issue if needed. We value issue reports, and this procedure is meant to help us resurface and prioritize issues that have not been addressed yet, not make them disappear. Thanks for your help!

What is the way forward here? As far as I've understood, svg does not support gouraud shading unless you rasterize the surface.

Minimal idea: Can we check the state upon rendering and issue a warning when gouraud shading is used without rasterization?
If anybody wants to look into this: Likely RendererSVG.draw_grouraud_triangles is the place to check.