[Bf-blender-cvs] [8f327fb0700] soc-2019-openxr: Cleanup: Add comments on GPU data and Ghost context usage

[Julian Eisel]

Commit: 8f327fb070044984a140ce958cdcbdf934d3c3f6
Author: Julian Eisel
Date:   Wed Mar 11 14:14:00 2020 +0100
Branches: soc-2019-openxr
https://developer.blender.org/rB8f327fb070044984a140ce958cdcbdf934d3c3f6

Cleanup: Add comments on GPU data and Ghost context usage

===================================================================

M	intern/ghost/GHOST_C-api.h
M	source/blender/windowmanager/intern/wm_xr.c

===================================================================

diff --git a/intern/ghost/GHOST_C-api.h b/intern/ghost/GHOST_C-api.h
index aefb4403d54..aba5b5f733b 100644
--- a/intern/ghost/GHOST_C-api.h
+++ b/intern/ghost/GHOST_C-api.h
@@ -762,7 +762,9 @@ extern GHOST_TSuccess GHOST_ReleaseOpenGLContext(GHOST_ContextHandle contexthand
 extern unsigned int GHOST_GetContextDefaultOpenGLFramebuffer(GHOST_ContextHandle contexthandle);
 
 /**
- * Returns whether a context is rendered upside down compared to OpenGL.
+ * Returns whether a context is rendered upside down compared to OpenGL. This only needs to be
+ * called if there's a non-OpenGL context, which is really the exception.
+ * So generally, this does not need to be called.
  */
 extern int GHOST_isUpsideDownContext(GHOST_ContextHandle contexthandle);
 
diff --git a/source/blender/windowmanager/intern/wm_xr.c b/source/blender/windowmanager/intern/wm_xr.c
index bd80e668258..d90d513ff6c 100644
--- a/source/blender/windowmanager/intern/wm_xr.c
+++ b/source/blender/windowmanager/intern/wm_xr.c
@@ -471,8 +471,14 @@ void wm_xr_draw_view(const GHOST_XrDrawViewInfo *draw_view, void *customdata)
                                   surface_data->offscreen,
                                   surface_data->viewport);
 
-  /* Re-use the offscreen framebuffer to render the composited viewport into. Keep it bound,
-   * Ghost-XR will then blit from the currently bound framebuffer into the OpenXR swapchain. */
+  /* The draw-manager uses both GPUOffscreen and GPUViewport to manage frame and texture buffers. A
+   * call to GPU_viewport_draw_to_screen() is still needed to get the final result from the
+   * viewport buffers composited together and potentially color managed for display on screen.
+   * It needs a bound framebuffer to draw into, for which we simply reuse the GPUOffscreen one.
+   *
+   * In a next step, Ghost-XR will use the the currently bound framebuffer to retrieve the image to
+   * be submitted to the OpenXR swapchain. So do not un-bind the offscreen yet! */
+
   GPU_offscreen_bind(surface_data->offscreen, false);
 
   wm_xr_draw_viewport_buffers_to_active_framebuffer(surface_data, draw_view);