Strange patch behaviour when hgtransform applied to object

Hi,

I have a patch surface consisting of triangular facets. I have a scalar field for with data for each node in the patch. This is used to generate a fringe plot. This has been working well.

p = patch(surf, ...
  'cdata', field_values, ...
  'facecolor','interp', ...
  'facelighting', 'phong', ...
  'edgecolor', 'none',...
  'specularstrength', 0.1);
axis equal; 
set(gca, 'visible', 'off');
caxis(color_scale)
colorbar('location', 'eastoutside');
light

I require orthogonal views of this patch surface. I tried to use hgtransform to re-orient the patch as follows:

% hg=hgtransform;
% set(p,'parent', hg);
% M = makehgtform('yrotate',-pi/2);
% set(hg, 'matrix', M);

The patch surface orients correctly, however the face shading is now distorted, which I guess is due to the vertex normals not updating to the new orientation.

Have I missed something, or is this an inappropriate use of this command, and I would be better off using the camera toolbar.

Thanks for any comments.

Regards Andrew Sims UNSW, Australia.

Answer 1

[Patrick Kalita]

I think this is probably a bug in how the ZBuffer renderer does its lighting computations. If you change the figure's renderer to OpenGL, it should look fine:

set(gcf, 'Renderer', 'OpenGL')

One caveat: the OpenGL renderer does not support Phong lighting. So you will notice that even though the patch's FaceLighting property is set to 'phong' it will fall back to Gouraud-style shading when you change renderers.

[Andrew]

Thank you Patrick. That is very helpful.

Regards

Andrew Sims