shaders are always constant, it appears

panda/src/pgraph/nodePath.cxx

@@ -3138,7 +3138,7 @@ get_texture(TextureStage *stage) const {
 //  Description: 
 ////////////////////////////////////////////////////////////////////
 void NodePath::
-set_shader(Shader *sha, int priority) {
+set_shader(const Shader *sha, int priority) {
   nassertv_always(!is_empty());
 
   const RenderAttrib *attrib =

panda/src/pgraph/nodePath.h

@@ -564,7 +564,7 @@ PUBLISHED:
   Texture *get_texture() const;
   Texture *get_texture(TextureStage *stage) const;
 
-  void set_shader(Shader *sha, int priority = 0);
+  void set_shader(const Shader *sha, int priority = 0);
   void set_shader_off(int priority = 0);
   void clear_shader();
   void set_shader_input(const ShaderInput *inp);