glgsg: add support for p3d_FragData fragment output

This is necessary for GLSL 1.30 which deprecates gl_FragData but does not yet support layout(location=) specifiers

Also fix some function pointer checks for pre-GL 3.0

Fixes #455

panda/src/glstuff/glGraphicsStateGuardian_src.cxx

@@ -1754,14 +1754,6 @@ reset() {
        get_extension_func("glUniform3iv");
     _glUniform4iv = (PFNGLUNIFORM4IVPROC)
        get_extension_func("glUniform4iv");
-    _glUniform1uiv = (PFNGLUNIFORM1UIVPROC)
-       get_extension_func("glUniform1uiv");
-    _glUniform2uiv = (PFNGLUNIFORM2UIVPROC)
-       get_extension_func("glUniform2uiv");
-    _glUniform3uiv = (PFNGLUNIFORM3UIVPROC)
-       get_extension_func("glUniform3uiv");
-    _glUniform4uiv = (PFNGLUNIFORM4UIVPROC)
-       get_extension_func("glUniform4uiv");
     _glUniformMatrix3fv = (PFNGLUNIFORMMATRIX3FVPROC)
        get_extension_func("glUniformMatrix3fv");
     _glUniformMatrix4fv = (PFNGLUNIFORMMATRIX4FVPROC)
@@ -1776,9 +1768,35 @@ reset() {
        get_extension_func("glVertexAttribPointer");
 
     if (is_at_least_gl_version(3, 0)) {
+      _glBindFragDataLocation = (PFNGLBINDFRAGDATALOCATIONPROC)
+         get_extension_func("glBindFragDataLocation");
       _glVertexAttribIPointer = (PFNGLVERTEXATTRIBIPOINTERPROC)
          get_extension_func("glVertexAttribIPointer");
+      _glUniform1uiv = (PFNGLUNIFORM1UIVPROC)
+         get_extension_func("glUniform1uiv");
+      _glUniform2uiv = (PFNGLUNIFORM2UIVPROC)
+         get_extension_func("glUniform2uiv");
+      _glUniform3uiv = (PFNGLUNIFORM3UIVPROC)
+         get_extension_func("glUniform3uiv");
+      _glUniform4uiv = (PFNGLUNIFORM4UIVPROC)
+         get_extension_func("glUniform4uiv");
+
+    } else if (has_extension("GL_EXT_gpu_shader4")) {
+      _glBindFragDataLocation = (PFNGLBINDFRAGDATALOCATIONPROC)
+         get_extension_func("glBindFragDataLocationEXT");
+      _glVertexAttribIPointer = (PFNGLVERTEXATTRIBIPOINTERPROC)
+         get_extension_func("glVertexAttribIPointerEXT");
+      _glUniform1uiv = (PFNGLUNIFORM1UIVPROC)
+         get_extension_func("glUniform1uivEXT");
+      _glUniform2uiv = (PFNGLUNIFORM2UIVPROC)
+         get_extension_func("glUniform2uivEXT");
+      _glUniform3uiv = (PFNGLUNIFORM3UIVPROC)
+         get_extension_func("glUniform3uivEXT");
+      _glUniform4uiv = (PFNGLUNIFORM4UIVPROC)
+         get_extension_func("glUniform4uivEXT");
+
     } else {
+      _glBindFragDataLocation = nullptr;
       _glVertexAttribIPointer = nullptr;
     }
     if (is_at_least_gl_version(4, 1) ||
@@ -1807,6 +1825,7 @@ reset() {
     _glVertexAttribPointer = (PFNGLVERTEXATTRIBPOINTERPROC)
        get_extension_func("glVertexAttribPointerARB");
 
+    _glBindFragDataLocation = nullptr;
     _glVertexAttribIPointer = nullptr;
     _glVertexAttribLPointer = nullptr;
   }
@@ -1858,6 +1877,13 @@ reset() {
   } else {
     _glVertexAttribIPointer = nullptr;
   }
+
+  if (has_extension("GL_EXT_blend_func_extended")) {
+    _glBindFragDataLocation = (PFNGLBINDFRAGDATALOCATIONPROC)
+       get_extension_func("glBindFragDataLocationEXT");
+  } else {
+    _glBindFragDataLocation = nullptr;
+  }
 #endif
 
 #ifndef OPENGLES_1

panda/src/glstuff/glGraphicsStateGuardian_src.h

@@ -146,6 +146,7 @@ typedef void (APIENTRYP PFNGLBLENDFUNCSEPARATEPROC) (GLenum sfactorRGB, GLenum d
 // GLSL shader functions
 typedef void (APIENTRYP PFNGLATTACHSHADERPROC) (GLuint program, GLuint shader);
 typedef void (APIENTRYP PFNGLBINDATTRIBLOCATIONPROC) (GLuint program, GLuint index, const GLchar *name);
+typedef void (APIENTRYP PFNGLBINDFRAGDATALOCATIONPROC) (GLuint program, GLuint color, const GLchar *name);
 typedef void (APIENTRYP PFNGLCOMPILESHADERPROC) (GLuint shader);
 typedef GLuint (APIENTRYP PFNGLCREATEPROGRAMPROC) (void);
 typedef GLuint (APIENTRYP PFNGLCREATESHADERPROC) (GLenum type);
@@ -963,6 +964,7 @@ public:
   // GLSL functions
   PFNGLATTACHSHADERPROC _glAttachShader;
   PFNGLBINDATTRIBLOCATIONPROC _glBindAttribLocation;
+  PFNGLBINDFRAGDATALOCATIONPROC _glBindFragDataLocation;
   PFNGLCOMPILESHADERPROC _glCompileShader;
   PFNGLCREATEPROGRAMPROC _glCreateProgram;
   PFNGLCREATESHADERPROC _glCreateShader;

panda/src/glstuff/glShaderContext_src.cxx

@@ -3219,6 +3219,11 @@ glsl_compile_and_link() {
     _glgsg->_glBindAttribLocation(_glsl_program, 8, "texcoord");
   }
 
+  // Also bind the p3d_FragData array to the first index always.
+  if (_glgsg->_glBindFragDataLocation != nullptr) {
+    _glgsg->_glBindFragDataLocation(_glsl_program, 0, "p3d_FragData");
+  }
+
   // If we requested to retrieve the shader, we should indicate that before
   // linking.
   bool retrieve_binary = false;