[PATCH 3/4] Generate swrast GLX extension list, rather than using a fixed list

[Jon TURNEY]

Ensure this kind of bug doesn't occur in future, by generating the GLX extension
list for swrast, in the same way as dri and dri2 do, rather than using a fixed
list of GLX extensions for swrast.

We explicity select the extensions reported by swrast rather than using
__glXInitExtensionEnableBits(), to maintain the historical behaviour, which is
slightly different:

- GLX_SGIS_multisample is not reported on APPLE
- GLX_SGIX_visual_select_group isn't reported

(How swrast handles GLX_MESA_copy_sub_buffer still looks a bit wonky: We always
enable it, but then subsequently also check if the loaded driver supports it,
and if it doesn't all glxCopySubBufferMESA() calls are just going to fail
GLXBadDrawable as the copySubBuffer function pointer is NULL.  This probably
isn't a practical concern.)

Signed-off-by: Jon TURNEY <jon.turney at dronecode.org.uk>
---
 glx/glxdriswrast.c |   36 ++++++++++++++++++++++++++++++++++++
 glx/glxscreens.c   |   14 +-------------
 2 files changed, 37 insertions(+), 13 deletions(-)

diff --git a/glx/glxdriswrast.c b/glx/glxdriswrast.c
index b478398..d5cfaf1 100644
--- a/glx/glxdriswrast.c
+++ b/glx/glxdriswrast.c
@@ -75,6 +75,8 @@ struct __GLXDRIscreen {
     const __DRIcopySubBufferExtension *copySubBuffer;
     const __DRItexBufferExtension *texBuffer;
     const __DRIconfig **driConfigs;
+
+    unsigned char glx_enable_bits[__GLX_EXT_BYTES];
 };
 
 struct __GLXDRIcontext {
@@ -434,6 +436,7 @@ __glXDRIscreenProbe(ScreenPtr pScreen)
 {
     const char *driverName = "swrast";
     __GLXDRIscreen *screen;
+    size_t buffer_size;
 
     screen = calloc(1, sizeof *screen);
     if (screen == NULL)
@@ -445,6 +448,26 @@ __glXDRIscreenProbe(ScreenPtr pScreen)
     screen->base.swapInterval = NULL;
     screen->base.pScreen = pScreen;
 
+    /*
+      Rather than calling __glXInitExtensionEnableBits, we explicitly enable a
+      specific set of extensions here to maintain the historical behaviour, which
+      is slightly different.
+    */
+    __glXEnableExtension(screen->glx_enable_bits, "GLX_ARB_multisample");
+    __glXEnableExtension(screen->glx_enable_bits, "GLX_EXT_visual_info");
+    __glXEnableExtension(screen->glx_enable_bits, "GLX_EXT_visual_rating");
+    __glXEnableExtension(screen->glx_enable_bits, "GLX_EXT_import_context");
+    __glXEnableExtension(screen->glx_enable_bits, "GLX_EXT_texture_from_pixmap");
+    __glXEnableExtension(screen->glx_enable_bits, "GLX_OML_swap_method");
+    __glXEnableExtension(screen->glx_enable_bits, "GLX_SGI_make_current_read");
+#ifndef __APPLE__
+    __glXEnableExtension(screen->glx_enable_bits, "GLX_SGIS_multisample");
+#endif
+    __glXEnableExtension(screen->glx_enable_bits, "GLX_SGIX_fbconfig");
+    __glXEnableExtension(screen->glx_enable_bits, "GLX_SGIX_pbuffer");
+    __glXEnableExtension(screen->glx_enable_bits, "GLX_SGIX_visual_select_group");
+    __glXEnableExtension(screen->glx_enable_bits, "GLX_MESA_copy_sub_buffer");
+
     screen->driver = glxProbeDriver(driverName,
                                     (void **) &screen->core,
                                     __DRI_CORE, __DRI_CORE_VERSION,
@@ -473,6 +496,19 @@ __glXDRIscreenProbe(ScreenPtr pScreen)
 
     __glXScreenInit(&screen->base, pScreen);
 
+    /* The first call simply determines the length of the extension string.
+     * This allows us to allocate some memory to hold the extension string,
+     * but it requires that we call __glXGetExtensionString a second time.
+     */
+    buffer_size = __glXGetExtensionString(screen->glx_enable_bits, NULL);
+    if (buffer_size > 0) {
+        free(screen->base.GLXextensions);
+
+        screen->base.GLXextensions = xnfalloc(buffer_size);
+        (void) __glXGetExtensionString(screen->glx_enable_bits,
+                                       screen->base.GLXextensions);
+    }
+
     screen->base.GLXmajor = 1;
     screen->base.GLXminor = 4;
 
diff --git a/glx/glxscreens.c b/glx/glxscreens.c
index 037b037..3ca2105 100644
--- a/glx/glxscreens.c
+++ b/glx/glxscreens.c
@@ -163,18 +163,6 @@ static const char GLServerExtensions[] =
 static char GLXServerVendorName[] = "SGI";
 unsigned glxMajorVersion = SERVER_GLX_MAJOR_VERSION;
 unsigned glxMinorVersion = SERVER_GLX_MINOR_VERSION;
-static char GLXServerExtensions[] =
-    "GLX_ARB_multisample "
-    "GLX_EXT_visual_info "
-    "GLX_EXT_visual_rating "
-    "GLX_EXT_import_context "
-    "GLX_EXT_texture_from_pixmap "
-    "GLX_OML_swap_method " "GLX_SGI_make_current_read "
-#ifndef __APPLE__
-    "GLX_SGIS_multisample "
-#endif
-    "GLX_SGIX_fbconfig "
-    "GLX_SGIX_pbuffer " "GLX_MESA_copy_sub_buffer ";
 
 static Bool
 glxCloseScreen(ScreenPtr pScreen)
@@ -328,7 +316,7 @@ __glXScreenInit(__GLXscreen * pGlxScreen, ScreenPtr pScreen)
     pGlxScreen->pScreen = pScreen;
     pGlxScreen->GLextensions = strdup(GLServerExtensions);
     pGlxScreen->GLXvendor = strdup(GLXServerVendorName);
-    pGlxScreen->GLXextensions = strdup(GLXServerExtensions);
+    pGlxScreen->GLXextensions = strdup("");
 
     /* All GLX providers must support all of the functionality required for at
      * least GLX 1.2.  If the provider supports a higher version, the GLXminor
-- 
1.7.9