dmabuf: Allow implicit modifiers

Remove all the roadblocks we've put up to keep implicit modifiers
out. Our importing code already handles them as a signal that says
'No modifiers, please!'. Now we just hope for the best and pass
things along.

This is necessary since some drivers won't produce any explicit
modifiers.

gdk/gdkdmabuf.c

@@ -559,11 +559,10 @@ gdk_dmabuf_get_direct_downloader (void)
  *
  * 1. Disallow any dmabuf format that we do not know.
  *
- * 1. Reject the INVALID modifier, accept the LINEAR one.
+ * 2. Ignore non-linear modifiers.
  *
- * 2. Ignore all other modifiers.
- *
- * 3. Try and fix various inconsistencies between V4L and Mesa, like NV12.
+ * 3. Try and fix various inconsistencies between V4L and Mesa
+ *    for linear modifiers, like the e.g. single-plane NV12.
  *
  * *** WARNING ***
  *
@@ -592,14 +591,6 @@ gdk_dmabuf_sanitize (GdkDmabuf        *dest,
       return FALSE;
     }
 
-  if (src->modifier == DRM_FORMAT_MOD_INVALID)
-    {
-      g_set_error (error,
-                   GDK_DMABUF_ERROR, GDK_DMABUF_ERROR_UNSUPPORTED_FORMAT,
-                   "GTK does not support the INVALID modifier.");
-      return FALSE;
-    }
-
   info = get_drm_format_info (src->fourcc);
 
   if (info == NULL)

gdk/gdkdmabufegl.c

@@ -113,6 +113,12 @@ gdk_dmabuf_egl_downloader_collect_formats (const GdkDmabufDownloader *downloader
           if (external_only[j])
             gdk_dmabuf_formats_builder_add_format (external, fourccs[i], modifiers[j]);
         }
+
+      /* Accept implicit modifiers as long as we accept the format at all.
+       * This is a bit of a crapshot, but unfortunately needed for a bunch
+       * of drivers.
+       */
+      gdk_dmabuf_formats_builder_add_format (formats, fourccs[i], DRM_FORMAT_MOD_INVALID);
     }
 
   g_free (modifiers);

gdk/gdkdmabufformats.c

@@ -37,6 +37,10 @@
  * The list of supported formats is sorted by preference,
  * with the best formats coming first.
  *
+ * The list may contains (format, modfier) pairs where the modifier
+ * is `DMA_FORMAT_MOD_INVALID`, indicating that **_implicit modifiers_**
+ * may be used with this format.
+ *
  * See [class@Gdk.DmabufTextureBuilder] for more information
  * about DMA buffers.
  *

gdk/gdkdmabufformatsbuilder.c

@@ -22,9 +22,6 @@
 
 #include "gdkdmabufformatsprivate.h"
 
-#ifdef HAVE_DMABUF
-#include <drm_fourcc.h>
-#endif
 
 #define GDK_ARRAY_NAME gdk_dmabuf_formats_builder
 #define GDK_ARRAY_TYPE_NAME GdkDmabufFormatsBuilder
@@ -121,12 +118,6 @@ gdk_dmabuf_formats_builder_add_format (GdkDmabufFormatsBuilder *self,
                                        guint32                  fourcc,
                                        guint64                  modifier)
 {
-#ifdef HAVE_DMABUF
-  g_return_if_fail (modifier != DRM_FORMAT_MOD_INVALID);
-#else
-  g_return_if_reached ();
-#endif
-
   gdk_dmabuf_formats_builder_append (self, &(GdkDmabufFormat) { fourcc, modifier });
 }
 

gdk/gdkdmabuftexturebuilder.c

@@ -29,8 +29,6 @@
 #include <cairo-gobject.h>
 #ifdef HAVE_DMABUF
 #include <drm_fourcc.h>
-#else
-#define DRM_FORMAT_MOD_INVALID ((1ULL << 56) - 1)
 #endif
 
 
@@ -90,6 +88,10 @@ struct _GdkDmabufTextureBuilderClass
  * characters. Additionally, each DMA buffer has a **_modifier_**, which is a 64-bit integer
  * that describes driver-specific details of the memory layout, such as tiling or compression.
  *
+ * For historical reasons, some producers of dma-bufs don't provide an explicit modifier, but
+ * instead return `DMA_FORMAT_MOD_INVALID` to indicate that their modifier is **_impliict_**.
+ * GTK tries to accomodate this situation by accepting `DMA_FORMAT_MOD_INVALID` as modifier.
+ *
  * The operation of `GdkDmabufTextureBuilder` is quite simple: Create a texture builder,
  * set all the necessary properties, and then call [method@Gdk.DmabufTextureBuilder.build]
  * to create the new texture.
@@ -611,13 +613,6 @@ gdk_dmabuf_texture_builder_set_modifier (GdkDmabufTextureBuilder *self,
                                          guint64                  modifier)
 {
   g_return_if_fail (GDK_IS_DMABUF_TEXTURE_BUILDER (self));
-  if (modifier == DRM_FORMAT_MOD_INVALID)
-    {
-      g_critical ("GTK does not support the INVALID modifier. "
-                  "If you use code that produces it, it should include "
-                  "instructions how to transform it into a regular modifier.");
-      return;
-    }
 
   if (self->dmabuf.modifier == modifier)
     return;