Use the old GLSL extensions if GL 2.0 is not available

Some drivers have good support for GLSL but don't have the complete
set of features needed to advertise GL 2.0 support. We should accept
the three old GLSL extensions (GL_ARB_shader_objects,
GL_ARB_vertex_shader and GL_ARB_fragment_shader) to support shaders on
these drivers.

This patch splits the shader functions into four sections :- those
that are provided only in GL 2.0, those that have the same name in the
shader objects extension, those that are provided by the vertex
shader extension (they all share the same name) and those that have a
different name in the shader objects extension.

If GL 2.0 is not supported but all three of the extensions are then
the pointers to the GL2-only functions will be replaced to point to
the equivalent functions from the extensions. That way the rest of the
Cogl source doesn't have to worry about the name differences.

https://bugzilla.gnome.org/show_bug.cgi?id=677078

Reviewed-by: Robert Bragg <robert@linux.intel.com>

(cherry picked from commit 71ecb51bd20dc3053b4221961b57e5a2b1029bdf)

cogl/driver/gl/cogl-gl.c

@@ -424,6 +424,33 @@ _cogl_driver_update_features (CoglContext *ctx,
       flags |= COGL_FEATURE_SHADERS_GLSL;
       COGL_FLAGS_SET (ctx->features, COGL_FEATURE_ID_GLSL, TRUE);
     }
+  /* If all of the old GLSL extensions are available then we can fake
+   * the GL 2.0 GLSL support by diverting to the old function names */
+  else if (ctx->glCreateProgramObject && /* GL_ARB_shader_objects */
+           ctx->glVertexAttribPointer && /* GL_ARB_vertex_shader */
+           _cogl_check_extension ("GL_ARB_fragment_shader", gl_extensions))
+    {
+      ctx->glCreateShader = ctx->glCreateShaderObject;
+      ctx->glCreateProgram = ctx->glCreateProgramObject;
+      ctx->glDeleteShader = ctx->glDeleteObject;
+      ctx->glDeleteProgram = ctx->glDeleteObject;
+      ctx->glAttachShader = ctx->glAttachObject;
+      ctx->glUseProgram = ctx->glUseProgramObject;
+      ctx->glGetProgramInfoLog = ctx->glGetInfoLog;
+      ctx->glGetShaderInfoLog = ctx->glGetInfoLog;
+      ctx->glGetShaderiv = ctx->glGetObjectParameteriv;
+      ctx->glGetProgramiv = ctx->glGetObjectParameteriv;
+      ctx->glDetachShader = ctx->glDetachObject;
+      ctx->glGetAttachedShaders = ctx->glGetAttachedObjects;
+      /* FIXME: there doesn't seem to be an equivalent for glIsShader
+       * and glIsProgram. This doesn't matter for now because Cogl
+       * doesn't use these but if we add support for simulating a
+       * GLES2 context on top of regular GL then we'll need to do
+       * something here */
+
+      flags |= COGL_FEATURE_SHADERS_GLSL;
+      COGL_FLAGS_SET (ctx->features, COGL_FEATURE_ID_GLSL, TRUE);
+    }
 
   if (ctx->glGenBuffers)
     {

cogl/gl-prototypes/cogl-all-functions.h

@@ -229,3 +229,38 @@ COGL_EXT_FUNCTION (void, glSamplerParameteri,
                     GLenum pname,
                     GLint param))
 COGL_EXT_END ()
+
+/* These only list functions that come from the old GLSL extensions.
+ * Functions that are common to the extensions and GLSL 2.0 should
+ * instead be listed in cogl-glsl-functions.h */
+COGL_EXT_BEGIN (shader_objects, 255, 255,
+                0, /* not in either GLES */
+                "ARB\0",
+                "shader_objects")
+COGL_EXT_FUNCTION (GLuint, glCreateProgramObject,
+                   (void))
+COGL_EXT_FUNCTION (GLuint, glCreateShaderObject,
+                   (GLenum shaderType))
+COGL_EXT_FUNCTION (void, glDeleteObject,
+                   (GLuint obj))
+COGL_EXT_FUNCTION (void, glAttachObject,
+                   (GLuint container, GLuint obj))
+COGL_EXT_FUNCTION (void, glUseProgramObject,
+                   (GLuint programObj))
+COGL_EXT_FUNCTION (void, glGetInfoLog,
+                   (GLuint                obj,
+                    GLsizei               maxLength,
+                    GLsizei              *length,
+                    char                 *infoLog))
+COGL_EXT_FUNCTION (void, glGetObjectParameteriv,
+                   (GLuint                obj,
+                    GLenum                pname,
+                    GLint                *params))
+COGL_EXT_FUNCTION (void, glDetachObject,
+                   (GLuint container, GLuint obj))
+COGL_EXT_FUNCTION (void, glGetAttachedObjects,
+                   (GLuint program,
+                    GLsizei maxcount,
+                    GLsizei* count,
+                    GLuint* shaders))
+COGL_EXT_END ()

cogl/gl-prototypes/cogl-glsl-functions.h

@@ -49,9 +49,9 @@
  * extensions match then it will be used.
  */
 
-/* The function names in OpenGL 2.0 are different so we can't easily
+/* This lists functions that are unique to GL 2.0 or GLES 2.0 and are
-   just check for GL 2.0 */
+ * not in the old GLSL extensions */
-COGL_EXT_BEGIN (shaders_glsl, 2, 0,
+COGL_EXT_BEGIN (shaders_glsl_2_only, 2, 0,
                 COGL_EXT_IN_GLES2,
                 "\0",
                 "\0")
@@ -59,25 +59,13 @@ COGL_EXT_FUNCTION (GLuint, glCreateProgram,
                    (void))
 COGL_EXT_FUNCTION (GLuint, glCreateShader,
                    (GLenum                shaderType))
-COGL_EXT_FUNCTION (void, glShaderSource,
-                   (GLuint                shader,
-                    GLsizei               count,
-                    const char   * const *string,
-                    const GLint          *length))
-COGL_EXT_FUNCTION (void, glCompileShader,
-                   (GLuint                shader))
 COGL_EXT_FUNCTION (void, glDeleteShader,
                    (GLuint                shader))
 COGL_EXT_FUNCTION (void, glAttachShader,
                    (GLuint                program,
                     GLuint                shader))
-COGL_EXT_FUNCTION (void, glLinkProgram,
-                   (GLuint                program))
 COGL_EXT_FUNCTION (void, glUseProgram,
                    (GLuint                program))
-COGL_EXT_FUNCTION (GLint, glGetUniformLocation,
-                   (GLuint                program,
-                    const char           *name))
 COGL_EXT_FUNCTION (void, glDeleteProgram,
                    (GLuint                program))
 COGL_EXT_FUNCTION (void, glGetShaderInfoLog,
@@ -85,23 +73,50 @@ COGL_EXT_FUNCTION (void, glGetShaderInfoLog,
                     GLsizei               maxLength,
                     GLsizei              *length,
                     char                 *infoLog))
+COGL_EXT_FUNCTION (void, glGetProgramInfoLog,
+                   (GLuint                program,
+                    GLsizei               bufSize,
+                    GLsizei              *length,
+                    char                 *infoLog))
 COGL_EXT_FUNCTION (void, glGetShaderiv,
                    (GLuint                shader,
                     GLenum                pname,
                     GLint                *params))
+COGL_EXT_FUNCTION (void, glGetProgramiv,
+                   (GLuint                program,
+                    GLenum                pname,
+                    GLint                *params))
+COGL_EXT_FUNCTION (void, glDetachShader,
+                   (GLuint program, GLuint shader))
+COGL_EXT_FUNCTION (void, glGetAttachedShaders,
+                   (GLuint program,
+                    GLsizei maxcount,
+                    GLsizei* count,
+                    GLuint* shaders))
+COGL_EXT_FUNCTION (GLboolean, glIsShader,
+                   (GLuint shader))
+COGL_EXT_FUNCTION (GLboolean, glIsProgram,
+                   (GLuint program))
+COGL_EXT_END ()
 
-COGL_EXT_FUNCTION (void, glVertexAttribPointer,
+/* These functions are provided by GL_ARB_shader_objects or are in GL
-                   (GLuint		 index,
+ * 2.0 core */
-                    GLint		 size,
+COGL_EXT_BEGIN (shader_objects_or_gl2, 2, 0,
-                    GLenum		 type,
+                COGL_EXT_IN_GLES2,
-                    GLboolean		 normalized,
+                "ARB\0",
-                    GLsizei		 stride,
+                "shader_objects\0")
-                    const GLvoid		*pointer))
+COGL_EXT_FUNCTION (void, glShaderSource,
-COGL_EXT_FUNCTION (void, glEnableVertexAttribArray,
+                   (GLuint                shader,
-                   (GLuint		 index))
+                    GLsizei               count,
-COGL_EXT_FUNCTION (void, glDisableVertexAttribArray,
+                    const char   * const *string,
-                   (GLuint		 index))
+                    const GLint          *length))
-
+COGL_EXT_FUNCTION (void, glCompileShader,
+                   (GLuint                shader))
+COGL_EXT_FUNCTION (void, glLinkProgram,
+                   (GLuint                program))
+COGL_EXT_FUNCTION (GLint, glGetUniformLocation,
+                   (GLuint                program,
+                    const char           *name))
 COGL_EXT_FUNCTION (void, glUniform1f,
                    (GLint                 location,
                     GLfloat               v0))
@@ -194,18 +209,39 @@ COGL_EXT_FUNCTION (void, glGetUniformiv,
                    (GLuint                program,
                     GLint                 location,
                     GLint                *params))
-
+COGL_EXT_FUNCTION (void, glGetActiveUniform,
-COGL_EXT_FUNCTION (void, glGetProgramiv,
                    (GLuint program,
-                    GLenum                pname,
+                    GLuint index,
-                    GLint                *params))
+                    GLsizei bufsize,
-
-COGL_EXT_FUNCTION (void, glGetProgramInfoLog,
-                   (GLuint                program,
-                    GLsizei               bufSize,
                     GLsizei* length,
-                    char                 *infoLog))
+                    GLint* size,
+                    GLenum* type,
+                    GLchar* name))
+COGL_EXT_FUNCTION (void, glGetShaderSource,
+                   (GLuint shader,
+                    GLsizei bufsize,
+                    GLsizei* length,
+                    GLchar* source))
+COGL_EXT_FUNCTION (void, glValidateProgram, (GLuint program))
+COGL_EXT_END ()
 
+/* These functions are provided by GL_ARB_vertex_shader or are in GL
+ * 2.0 core */
+COGL_EXT_BEGIN (vertex_shaders, 2, 0,
+                COGL_EXT_IN_GLES2,
+                "ARB\0",
+                "vertex_shader\0")
+COGL_EXT_FUNCTION (void, glVertexAttribPointer,
+                   (GLuint		 index,
+                    GLint		 size,
+                    GLenum		 type,
+                    GLboolean		 normalized,
+                    GLsizei		 stride,
+                    const GLvoid        *pointer))
+COGL_EXT_FUNCTION (void, glEnableVertexAttribArray,
+                   (GLuint		 index))
+COGL_EXT_FUNCTION (void, glDisableVertexAttribArray,
+                   (GLuint		 index))
 COGL_EXT_FUNCTION (void, glVertexAttrib1f, (GLuint indx, GLfloat x))
 COGL_EXT_FUNCTION (void, glVertexAttrib1fv,
                    (GLuint indx, const GLfloat* values))
@@ -220,17 +256,14 @@ COGL_EXT_FUNCTION (void, glVertexAttrib4f,
                    (GLuint index, GLfloat x, GLfloat y, GLfloat z, GLfloat w))
 COGL_EXT_FUNCTION (void, glVertexAttrib4fv,
                    (GLuint indx, const GLfloat* values))
-
 COGL_EXT_FUNCTION (void, glGetVertexAttribfv,
                    (GLuint index, GLenum pname, GLfloat* params))
 COGL_EXT_FUNCTION (void, glGetVertexAttribiv,
                    (GLuint index, GLenum pname, GLint* params))
 COGL_EXT_FUNCTION (void, glGetVertexAttribPointerv,
                    (GLuint index, GLenum pname, GLvoid** pointer))
-
 COGL_EXT_FUNCTION (GLint, glGetAttribLocation,
                    (GLuint program, const char *name))
-
 COGL_EXT_FUNCTION (void, glBindAttribLocation,
                    (GLuint program,
                     GLuint index,
@@ -243,32 +276,4 @@ COGL_EXT_FUNCTION (void, glGetActiveAttrib,
                     GLint* size,
                     GLenum* type,
                     GLchar* name))
-COGL_EXT_FUNCTION (void, glGetActiveUniform,
-                   (GLuint program,
-                    GLuint index,
-                    GLsizei bufsize,
-                    GLsizei* length,
-                    GLint* size,
-                    GLenum* type,
-                    GLchar* name))
-COGL_EXT_FUNCTION (void, glDetachShader,
-                   (GLuint program, GLuint shader))
-COGL_EXT_FUNCTION (void, glGetAttachedShaders,
-                   (GLuint program,
-                    GLsizei maxcount,
-                    GLsizei* count,
-                    GLuint* shaders))
-COGL_EXT_FUNCTION (void, glGetShaderSource,
-                   (GLuint shader,
-                    GLsizei bufsize,
-                    GLsizei* length,
-                    GLchar* source))
-
-COGL_EXT_FUNCTION (GLboolean, glIsShader,
-                   (GLuint shader))
-COGL_EXT_FUNCTION (GLboolean, glIsProgram,
-                   (GLuint program))
-
-COGL_EXT_FUNCTION (void, glValidateProgram, (GLuint program))
-
 COGL_EXT_END ()