cogl: Derive GLSL version from major, minor and GL vs GLES

The GLSL version can be derived from the major and the minor, with the
exception that GLSL ES versions require the "es" suffix.

Part-of: <https://gitlab.gnome.org/GNOME/mutter/-/merge_requests/3907>

cogl/cogl/cogl-context-private.h

@@ -79,14 +79,7 @@ struct _CoglContext
 
   int glsl_major;
   int glsl_minor;
-
-  /* This is the GLSL version that we will claim that snippets are
-   * written against using the #version pragma. This will be the
-   * largest version that is less than or equal to the version
-   * provided by the driver without massively altering the syntax. Eg,
-   * we wouldn't use version 1.3 even if it is available because that
-   * removes the ‘attribute’ and ‘varying’ keywords. */
-  int glsl_version_to_use;
+  gboolean glsl_es;
 
   /* Features cache */
   unsigned long features[COGL_FLAGS_N_LONGS_FOR_SIZE (_COGL_N_FEATURE_IDS)];

cogl/cogl/driver/gl/cogl-pipeline-vertend-glsl.c

@@ -188,6 +188,17 @@ add_layer_fragment_boilerplate_cb (CoglPipelineLayer *layer,
   return TRUE;
 }
 
+static char *
+glsl_version_string (CoglContext *ctx)
+{
+  gboolean needs_es_annotation = ctx->glsl_es && ctx->glsl_major > 1;
+
+  return g_strdup_printf ("%d%02d%s",
+                          ctx->glsl_major,
+                          ctx->glsl_minor,
+                          needs_es_annotation ? " es" : "");
+}
+
 void
 _cogl_glsl_shader_set_source_with_boilerplate (CoglContext *ctx,
                                                GLuint shader_gl_handle,
@@ -202,16 +213,17 @@ _cogl_glsl_shader_set_source_with_boilerplate (CoglContext *ctx,
 
   const char **strings = g_alloca (sizeof (char *) * (count_in + 4));
   GLint *lengths = g_alloca (sizeof (GLint) * (count_in + 4));
-  char *version_string;
+  g_autofree char *glsl_version = NULL;
+  g_autofree char *version_string = NULL;
   int count = 0;
-
   int n_layers;
 
   vertex_boilerplate = _COGL_VERTEX_SHADER_BOILERPLATE;
   fragment_boilerplate = _COGL_FRAGMENT_SHADER_BOILERPLATE;
 
-  version_string = g_strdup_printf ("#version %i\n\n",
-                                    ctx->glsl_version_to_use);
+  glsl_version = glsl_version_string (ctx);
+  version_string = g_strdup_printf ("#version %s\n\n", glsl_version);
+
   strings[count] = version_string;
   lengths[count++] = -1;
 
@@ -308,8 +320,6 @@ _cogl_glsl_shader_set_source_with_boilerplate (CoglContext *ctx,
 
   GE( ctx, glShaderSource (shader_gl_handle, count,
                            (const char **) strings, lengths) );
-
-  g_free (version_string);
 }
 GLuint
 _cogl_pipeline_vertend_glsl_get_shader (CoglPipeline *pipeline)

cogl/cogl/driver/gl/gl/cogl-driver-gl.c

@@ -482,7 +482,7 @@ _cogl_driver_update_features (CoglContext  *ctx,
 
   ctx->glsl_major = 1;
   ctx->glsl_minor = 40;
-  ctx->glsl_version_to_use = 140;
+  ctx->glsl_es = FALSE;
 
   if (!check_glsl_version (ctx, error))
     return FALSE;

cogl/cogl/driver/gl/gles/cogl-driver-gles.c

@@ -663,7 +663,7 @@ _cogl_driver_update_features (CoglContext  *context,
 
   context->glsl_major = 1;
   context->glsl_minor = 0;
-  context->glsl_version_to_use = 100;
+  context->glsl_es = TRUE;
 
   if (!check_glsl_version (context, error))
     return FALSE;