mesa: allow MESA_GL_VERSION_OVERRIDE to override the API type

Change the format to MAJOR.MINOR[FC]
For example: 2.1, 3.0FC, 3.1

The FC suffix indicates a forward compatible context, and
is only valid for versions >= 3.0.

Examples:
2.1:   GL Legacy/Compatibility context
3.0:   GL Legacy/Compatibility context
3.0FC: GL Core Profile context + Forward Compatible
3.1:   GL Core Profile context
3.1FC: GL Core Profile context + Forward Compatible

Signed-off-by: Jordan Justen <jordan.l.justen@intel.com>
Reviewed-by: Chad Versace <chad.versace@linux.intel.com>
Reviewed-by: Eric Anholt <eric@anholt.net>

docs/envvars.html

@@ -69,9 +69,25 @@ If the extension string is too long, the buffer overrun can cause the game
 to crash.
 This is a work-around for that.
 <li>MESA_GL_VERSION_OVERRIDE - changes the value returned by
-glGetString(GL_VERSION). Valid values are point-separated version numbers,
-such as "3.0". Mesa will not really implement all the features of the given
-version if it's higher than what's normally reported.
+glGetString(GL_VERSION) and possibly the GL API type.
+<ul>
+<li> The format should be MAJOR.MINOR[FC]
+<li> FC is an optional suffix that indicates a forward compatible context.
+This is only valid for versions &gt;= 3.0.
+<li> GL versions &lt; 3.0 are set to a compatibility (non-Core) profile
+<li> GL versions = 3.0, see below
+<li> GL versions &gt; 3.0 are set to a Core profile
+<li> Examples: 2.1, 3.0, 3.0FC, 3.1, 3.1FC
+<ul>
+<li> 2.1 - select a compatibility (non-Core) profile with GL version 2.1
+<li> 3.0 - select a compatibility (non-Core) profile with GL version 3.0
+<li> 3.0FC - select a Core+Forward Compatible profile with GL version 3.0
+<li> 3.1 - select a Core profile with GL version 3.1
+<li> 3.1FC - select a Core+Forward Compatible profile with GL version 3.1
+</ul>
+<li> Mesa may not really implement all the features of the given version.
+(for developers only)
+</ul>
 <li>MESA_GLSL_VERSION_OVERRIDE - changes the value returned by
 glGetString(GL_SHADING_LANGUAGE_VERSION). Valid values are integers, such as
 "130".  Mesa will not really implement all the features of the given language version

src/mesa/main/context.c

@@ -921,6 +921,10 @@ _mesa_initialize_context(struct gl_context *ctx,
    ctx->WinSysDrawBuffer = NULL;
    ctx->WinSysReadBuffer = NULL;
 
+   if (_mesa_is_desktop_gl(ctx)) {
+      _mesa_override_gl_version(ctx);
+   }
+
    /* misc one-time initializations */
    one_time_init(ctx);
 

src/mesa/main/version.c

@@ -28,30 +28,25 @@
 #include "git_sha1.h"
 
 /**
- * Override the context's GL version if the environment variable
- * MESA_GL_VERSION_OVERRIDE is set. Valid values of MESA_GL_VERSION_OVERRIDE
- * are point-separated version numbers, such as "3.0".
+ * Scans 'string' to see if it ends with 'ending'.
  */
-static void
-override_version(struct gl_context *ctx)
+static GLboolean
+check_for_ending(char *string, const char *ending)
 {
-   const char *env_var = "MESA_GL_VERSION_OVERRIDE";
-   const char *version;
-   int n;
-   int major, minor;
+   int len1, len2;
 
-   version = getenv(env_var);
-   if (!version) {
-      return;
+   len1 = strlen(string);
+   len2 = strlen(ending);
+
+   if (len2 > len1) {
+      return GL_FALSE;
    }
 
-   n = sscanf(version, "%u.%u", &major, &minor);
-   if (n != 2) {
-      fprintf(stderr, "error: invalid value for %s: %s\n", env_var, version);
-      return;
+   if (strcmp(string + (len1 - len2), ending) == 0) {
+      return GL_TRUE;
+   } else {
+      return GL_FALSE;
    }
-
-   ctx->Version = major * 10 + minor;
 }
 
 /**
@@ -77,6 +72,55 @@ create_version_string(struct gl_context *ctx, const char *prefix)
    }
 }
 
+/**
+ * Override the context's version and/or API type if the
+ * environment variable MESA_GL_VERSION_OVERRIDE is set.
+ *
+ * Example uses of MESA_GL_VERSION_OVERRIDE:
+ *
+ * 2.1: select a compatibility (non-Core) profile with GL version 2.1
+ * 3.0: select a compatibility (non-Core) profile with GL version 3.0
+ * 3.0FC: select a Core+Forward Compatible profile with GL version 3.0
+ * 3.1: select a Core profile with GL version 3.1
+ * 3.1FC: select a Core+Forward Compatible profile with GL version 3.1
+ */
+void
+_mesa_override_gl_version(struct gl_context *ctx)
+{
+   const char *env_var = "MESA_GL_VERSION_OVERRIDE";
+   const char *version;
+   int n;
+   int major, minor;
+   GLboolean fc_suffix;
+
+   version = getenv(env_var);
+   if (!version) {
+      return;
+   }
+
+   fc_suffix = check_for_ending(version, "FC");
+
+   n = sscanf(version, "%u.%u", &major, &minor);
+   if (n != 2) {
+      fprintf(stderr, "error: invalid value for %s: %s\n", env_var, version);
+   } else {
+      ctx->Version = major * 10 + minor;
+      if (ctx->Version < 30 && fc_suffix) {
+         fprintf(stderr, "error: invalid value for %s: %s\n", env_var, version);
+      } else {
+         if (ctx->Version >= 30 && fc_suffix) {
+            ctx->API = API_OPENGL_CORE;
+            ctx->Const.ContextFlags |= GL_CONTEXT_FLAG_FORWARD_COMPATIBLE_BIT;
+         } else if (ctx->Version >= 31) {
+            ctx->API = API_OPENGL_CORE;
+         } else {
+            ctx->API = API_OPENGL;
+         }
+         create_version_string(ctx, "");
+      }
+   }
+}
+
 /**
  * Override the context's GLSL version if the environment variable
  * MESA_GLSL_VERSION_OVERRIDE is set. Valid values for
@@ -244,8 +288,6 @@ compute_version(struct gl_context *ctx)
 
    ctx->Version = major * 10 + minor;
 
-   override_version(ctx);
-
    create_version_string(ctx, "");
 }
 

src/mesa/main/version.h

@@ -45,6 +45,9 @@ struct gl_context;
 extern void
 _mesa_compute_version(struct gl_context *ctx);
 
+extern void
+_mesa_override_gl_version(struct gl_context *ctx);
+
 extern void
 _mesa_override_glsl_version(struct gl_context *ctx);