docs: document 'useprog' debug option

diff --git a/docs/shading.html b/docs/shading.html
index 96060f1..bd02335 100644 (file)
--- a/docs/shading.html
+++ b/docs/shading.html
@@ -55,6 +55,7 @@ execution.  These are generally used for debugging.
     texcoord[0] attributes.
 <li>nopfrag - force fragment shader to be a simple shader that passes
     through the color attribute.
+<li>useprog - log glUseProgram calls to stderr
 </ul>
 <p>
 Example:  export MESA_GLSL=dump,nopt