glgsg: Fix skinning shader being unable to render unskinned models

Panda was adding a column with weights (0, 0, 0, 0), but these weights don't add up to 1 so no useful identity matrix can be produced.  Instead it's better to fall back to the OpenGL default, (0, 0, 0, 1).

I'm also defaulting the transform_index values to (0, 1, 2, 3) to support non-indexed skinning (although that's pretty esoteric, given that that only supports 4 transforms...)

panda/src/display/standardMunger.cxx

@@ -123,8 +123,9 @@ munge_data_impl(const GeomVertexData *data) {
   }
 
   GeomVertexAnimationSpec animation = new_data->get_format()->get_animation();
-  if (_shader_skinning || (_auto_shader && hardware_animated_vertices &&
-      !basic_shaders_only && animation.get_animation_type() == AT_panda)) {
+  if ((_shader_skinning && animation.get_animation_type() != AT_none) ||
+      (_auto_shader && hardware_animated_vertices &&
+       !basic_shaders_only && animation.get_animation_type() == AT_panda)) {
     animation.set_hardware(4, true);
 
   } else if (hardware_animated_vertices &&

panda/src/glstuff/glGraphicsStateGuardian_src.cxx

@@ -1909,6 +1909,8 @@ reset() {
          get_extension_func("glUniform3uiv");
       _glUniform4uiv = (PFNGLUNIFORM4UIVPROC)
          get_extension_func("glUniform4uiv");
+      _glVertexAttribI4ui = (PFNGLVERTEXATTRIBI4UIPROC)
+         get_extension_func("glVertexAttribI4ui");
 
     } else if (has_extension("GL_EXT_gpu_shader4")) {
       _glBindFragDataLocation = (PFNGLBINDFRAGDATALOCATIONPROC)
@@ -1923,10 +1925,13 @@ reset() {
          get_extension_func("glUniform3uivEXT");
       _glUniform4uiv = (PFNGLUNIFORM4UIVPROC)
          get_extension_func("glUniform4uivEXT");
+      _glVertexAttribI4ui = (PFNGLVERTEXATTRIBI4UIPROC)
+         get_extension_func("glVertexAttribI4uiEXT");
 
     } else {
       _glBindFragDataLocation = nullptr;
       _glVertexAttribIPointer = nullptr;
+      _glVertexAttribI4ui = nullptr;
     }
     if (is_at_least_gl_version(4, 1) ||
         has_extension("GL_ARB_vertex_attrib_64bit")) {
@@ -1955,8 +1960,11 @@ reset() {
        get_extension_func("glVertexAttribPointerARB");
 
     _glBindFragDataLocation = nullptr;
+    _glVertexAttribI4ui = nullptr;
     _glVertexAttribIPointer = nullptr;
     _glVertexAttribLPointer = nullptr;
+  } else {
+    _glVertexAttribI4ui = nullptr;
   }
 #endif
 
@@ -2003,8 +2011,11 @@ reset() {
   if (is_at_least_gles_version(3, 0)) {
     _glVertexAttribIPointer = (PFNGLVERTEXATTRIBIPOINTERPROC)
       get_extension_func("glVertexAttribIPointer");
+    _glVertexAttribI4ui = (PFNGLVERTEXATTRIBI4UIPROC)
+      get_extension_func("glVertexAttribI4ui");
   } else {
     _glVertexAttribIPointer = nullptr;
+    _glVertexAttribI4ui = nullptr;
   }
 
   if (has_extension("GL_EXT_blend_func_extended")) {

panda/src/glstuff/glGraphicsStateGuardian_src.h

@@ -186,6 +186,7 @@ typedef void (APIENTRYP PFNGLUNIFORMMATRIX4FVPROC) (GLint location, GLsizei coun
 typedef void (APIENTRYP PFNGLVALIDATEPROGRAMPROC) (GLuint program);
 typedef void (APIENTRYP PFNGLVERTEXATTRIB4FVPROC) (GLuint index, const GLfloat *v);
 typedef void (APIENTRYP PFNGLVERTEXATTRIB4DVPROC) (GLuint index, const GLdouble *v);
+typedef void (APIENTRYP PFNGLVERTEXATTRIBI4UIPROC) (GLuint index, GLuint x, GLuint y, GLuint z, GLuint w);
 typedef void (APIENTRYP PFNGLVERTEXATTRIBPOINTERPROC) (GLuint index, GLint size, GLenum type, GLboolean normalized, GLsizei stride, const GLvoid *pointer);
 typedef void (APIENTRYP PFNGLVERTEXATTRIBIPOINTERPROC) (GLuint index, GLint size, GLenum type, GLsizei stride, const GLvoid *pointer);
 typedef void (APIENTRYP PFNGLVERTEXATTRIBLPOINTERPROC) (GLuint index, GLint size, GLenum type, GLsizei stride, const GLvoid *pointer);
@@ -1010,6 +1011,7 @@ public:
   PFNGLVALIDATEPROGRAMPROC _glValidateProgram;
   PFNGLVERTEXATTRIB4FVPROC _glVertexAttrib4fv;
   PFNGLVERTEXATTRIB4DVPROC _glVertexAttrib4dv;
+  PFNGLVERTEXATTRIBI4UIPROC _glVertexAttribI4ui;
   PFNGLVERTEXATTRIBPOINTERPROC _glVertexAttribPointer;
   PFNGLVERTEXATTRIBIPOINTERPROC _glVertexAttribIPointer;
   PFNGLVERTEXATTRIBLPOINTERPROC _glVertexAttribLPointer;

panda/src/glstuff/glShaderContext_src.cxx

@@ -2529,6 +2529,10 @@ update_shader_vertex_arrays(ShaderContext *prev, bool force) {
           _glgsg->_glVertexAttrib4fv(p, _glgsg->_scene_graph_color.get_data());
 #endif
         }
+        else if (name == InternalName::get_transform_index() &&
+                 _glgsg->_glVertexAttribI4ui != nullptr) {
+          _glgsg->_glVertexAttribI4ui(p, 0, 1, 2, 3);
+        }
       }
     }