gdk: Add GDK_DEBUG=dmabuf-disable

I chose the name for consistency with gl-disable and vulkan-disable.

gdk/gdk.c

@@ -133,6 +133,7 @@ static const GdkDebugKey gdk_debug_keys[] = {
   { "default-settings",GDK_DEBUG_DEFAULT_SETTINGS, "Force default values for xsettings", TRUE },
   { "high-depth",      GDK_DEBUG_HIGH_DEPTH, "Use high bit depth rendering if possible", TRUE },
   { "no-vsync",        GDK_DEBUG_NO_VSYNC, "Repaint instantly (uses 100% CPU with animations)", TRUE },
+  { "dmabuf-disable",  GDK_DEBUG_DMABUF_DISABLE, "Disable dmabuf support", TRUE },
 };
 
 

gdk/gdkdebugprivate.h

@@ -53,6 +53,7 @@ typedef enum {
   GDK_DEBUG_DEFAULT_SETTINGS= 1 << 24,
   GDK_DEBUG_HIGH_DEPTH      = 1 << 25,
   GDK_DEBUG_NO_VSYNC        = 1 << 26,
+  GDK_DEBUG_DMABUF_DISABLE  = 1 << 27,
 } GdkDebugFlags;
 
 extern guint _gdk_debug_flags;

gdk/gdkdisplay.c

@@ -1851,11 +1851,14 @@ init_dmabuf_formats (GdkDisplay *display)
   if (display->dmabuf_formats != NULL)
     return;
 
-  gdk_display_prepare_gl (display, NULL);
-
   builder = gdk_dmabuf_formats_builder_new ();
 
-  gdk_dmabuf_texture_add_supported_formats (builder);
+  if (!GDK_DEBUG_CHECK (DMABUF_DISABLE))
+    {
+      gdk_display_prepare_gl (display, NULL);
+
+      gdk_dmabuf_texture_add_supported_formats (builder);
+    }
 
   display->dmabuf_formats = gdk_dmabuf_formats_builder_free_to_formats (builder);
 }

gdk/gdkdmabuftexturebuilder.c

@@ -21,6 +21,7 @@
 
 #include "gdkdmabuftexturebuilder.h"
 
+#include "gdkdebugprivate.h"
 #include "gdkdisplay.h"
 #include "gdkenumtypes.h"
 #include "gdkdmabuftextureprivate.h"
@@ -975,6 +976,13 @@ gdk_dmabuf_texture_builder_build (GdkDmabufTextureBuilder *self,
   for (int i = 0; i < self->n_planes; i++)
     g_return_val_if_fail (self->fds[i] != -1 || self->offsets[i] != 0, NULL);
 
+  if (GDK_DEBUG_CHECK (DMABUF_DISABLE))
+    {
+      g_set_error_literal (error, GDK_DMABUF_ERROR, GDK_DMABUF_ERROR_NOT_AVAILABLE,
+                           "dmabuf support disabled via GDK_DEBUG environment variable");
+      return NULL;
+    }
+
   return gdk_dmabuf_texture_new_from_builder (self, destroy, data, error);
 }