gallium/swrast: fix front buffer blitting. (v2)

So I've known this was broken before, cogl has a workaround
for it from what I know, but with the gallium based swrast
drivers BlitFramebuffer from back to front or vice-versa
was pretty broken.

The legacy swrast driver tracks when a front buffer is used
and does the get/put images when it is mapped/unmapped,
so this patch attempts to add the same functionality to the
gallium drivers.

It creates a new context interface to denote when a front
buffer is being created, and passes a private pointer to it,
this pointer is then used to decide on map/unmap if the
contents should be updated from the real frontbuffer using
get/put image.

This is primarily to make gtk's gl code work, the only
thing I've tested so far is the glarea test from
https://github.com/ebassi/glarea-example.git

v2: bump extension version,
check extension version before calling get image. (Ian)

Bugzilla: https://bugs.freedesktop.org/show_bug.cgi?id=91930

Cc: <[email protected]>
Signed-off-by: Dave Airlie <[email protected]>

3 files changed, 8 insertions, 0 deletions

diff --git a/src/gallium/include/pipe/p_screen.h b/src/gallium/include/pipe/p_screen.h
index a22fb938dbb..f868d71db23 100644
--- a/src/gallium/include/pipe/p_screen.h
+++ b/src/gallium/include/pipe/p_screen.h
@@ -169,6 +169,10 @@ struct pipe_screen {
    struct pipe_resource * (*resource_create)(struct pipe_screen *,
 					     const struct pipe_resource *templat);
 
+   struct pipe_resource * (*resource_create_front)(struct pipe_screen *,
+                                                   const struct pipe_resource *templat,
+                                                   const void *map_front_private);
+
    /**
     * Create a texture from a winsys_handle. The handle is often created in
     * another process by first creating a pipe texture and then calling
diff --git a/src/gallium/include/state_tracker/drisw_api.h b/src/gallium/include/state_tracker/drisw_api.h
index 328440cf5ff..cd5a27e2482 100644
--- a/src/gallium/include/state_tracker/drisw_api.h
+++ b/src/gallium/include/state_tracker/drisw_api.h
@@ -11,6 +11,9 @@ struct dri_drawable;
  */
 struct drisw_loader_funcs
 {
+   void (*get_image) (struct dri_drawable *dri_drawable,
+                      int x, int y, unsigned width, unsigned height, unsigned stride,
+                      void *data);
    void (*put_image) (struct dri_drawable *dri_drawable,
                       void *data, unsigned width, unsigned height);
    void (*put_image2) (struct dri_drawable *dri_drawable,
diff --git a/src/gallium/include/state_tracker/sw_winsys.h b/src/gallium/include/state_tracker/sw_winsys.h
index a3479eb0bc3..0b792cd0ce4 100644
--- a/src/gallium/include/state_tracker/sw_winsys.h
+++ b/src/gallium/include/state_tracker/sw_winsys.h
@@ -90,6 +90,7 @@ struct sw_winsys
                             enum pipe_format format,
                             unsigned width, unsigned height,
                             unsigned alignment,
+                            const void *front_private,
                             unsigned *stride );
 
    /**