loader_dri3/glx/egl: Reinstate the loader_dri3_vtable get_dri_screen callback

Removing this callback caused rendering corruption in some multi-screen cases,
so it is reinstated but without the drawable argument which was never used
by implementations and was confusing since the drawable could have been
created with another screen.

Cc: "17.3 18.0" mesa-stable@lists.freedesktop.org
Fixes: 5198e48a0d (loader_dri3/glx/egl: Remove the loader_dri3_vtable get_dri_screen callback)
Bugzilla: https://bugs.freedesktop.org/show_bug.cgi?id=105013
Reported-by: Daniel van Vugt <daniel.van.vugt@canonical.com>
Tested-by: Timo Aaltonen <tjaalton@ubuntu.com>
Signed-off-by: Thomas Hellstrom <thellstrom@vmware.com>
Reviewed-by: Brian Paul <brianp@vmware.com>

src/egl/drivers/dri2/platform_x11_dri3.c

@@ -75,6 +75,17 @@ egl_dri3_get_dri_context(struct loader_dri3_drawable *draw)
    return dri2_ctx->dri_context;
 }
 
+static __DRIscreen *
+egl_dri3_get_dri_screen(void)
+{
+   _EGLContext *ctx = _eglGetCurrentContext();
+   struct dri2_egl_context *dri2_ctx;
+   if (!ctx)
+      return NULL;
+   dri2_ctx = dri2_egl_context(ctx);
+   return dri2_egl_display(dri2_ctx->base.Resource.Display)->dri_screen;
+}
+
 static void
 egl_dri3_flush_drawable(struct loader_dri3_drawable *draw, unsigned flags)
 {
@@ -88,6 +99,7 @@ static const struct loader_dri3_vtable egl_dri3_vtable = {
    .set_drawable_size = egl_dri3_set_drawable_size,
    .in_current_context = egl_dri3_in_current_context,
    .get_dri_context = egl_dri3_get_dri_context,
+   .get_dri_screen = egl_dri3_get_dri_screen,
    .flush_drawable = egl_dri3_flush_drawable,
    .show_fps = NULL,
 };

src/glx/dri3_glx.c

@@ -116,6 +116,16 @@ glx_dri3_get_dri_context(struct loader_dri3_drawable *draw)
    return (gc != &dummyContext) ? dri3Ctx->driContext : NULL;
 }
 
+static __DRIscreen *
+glx_dri3_get_dri_screen(void)
+{
+   struct glx_context *gc = __glXGetCurrentContext();
+   struct dri3_context *pcp = (struct dri3_context *) gc;
+   struct dri3_screen *psc = (struct dri3_screen *) pcp->base.psc;
+
+   return (gc != &dummyContext && psc) ? psc->driScreen : NULL;
+}
+
 static void
 glx_dri3_flush_drawable(struct loader_dri3_drawable *draw, unsigned flags)
 {
@@ -150,6 +160,7 @@ static const struct loader_dri3_vtable glx_dri3_vtable = {
    .set_drawable_size = glx_dri3_set_drawable_size,
    .in_current_context = glx_dri3_in_current_context,
    .get_dri_context = glx_dri3_get_dri_context,
+   .get_dri_screen = glx_dri3_get_dri_screen,
    .flush_drawable = glx_dri3_flush_drawable,
    .show_fps = glx_dri3_show_fps,
 };

src/loader/loader_dri3_helper.c

@@ -1318,6 +1318,7 @@ dri3_get_pixmap_buffer(__DRIdrawable *driDrawable, unsigned int format,
    xcb_sync_fence_t                     sync_fence;
    struct xshmfence                     *shm_fence;
    int                                  fence_fd;
+   __DRIscreen                          *cur_screen;
 
    if (buffer)
       return buffer;
@@ -1348,8 +1349,17 @@ dri3_get_pixmap_buffer(__DRIdrawable *driDrawable, unsigned int format,
    if (!bp_reply)
       goto no_image;
 
+   /* Get the currently-bound screen or revert to using the drawable's screen if
+    * no contexts are currently bound. The latter case is at least necessary for
+    * obs-studio, when using Window Capture (Xcomposite) as a Source.
+    */
+   cur_screen = draw->vtable->get_dri_screen();
+   if (!cur_screen) {
+       cur_screen = draw->dri_screen;
+   }
+
    buffer->image = loader_dri3_create_image(draw->conn, bp_reply, format,
-                                            draw->dri_screen, draw->ext->image,
+                                            cur_screen, draw->ext->image,
                                             buffer);
    if (!buffer->image)
       goto no_image;

src/loader/loader_dri3_helper.h

@@ -99,6 +99,7 @@ struct loader_dri3_vtable {
    void (*set_drawable_size)(struct loader_dri3_drawable *, int, int);
    bool (*in_current_context)(struct loader_dri3_drawable *);
    __DRIcontext *(*get_dri_context)(struct loader_dri3_drawable *);
+   __DRIscreen *(*get_dri_screen)(void);
    void (*flush_drawable)(struct loader_dri3_drawable *, unsigned);
    void (*show_fps)(struct loader_dri3_drawable *, uint64_t);
 };