Use draw manager offscreen context for the VR session

This way we avoid the big overhead of context switches. Makes frames
render about twice as fast here. For heavy Spring scenes I'm getting
around 20 FPS here, classroom scene is at 50 FPS.
This is great given that drawing itself still isn't optimized for dual
eye rendering.

1 files changed, 11 insertions, 23 deletions

diff --git a/source/blender/windowmanager/intern/wm_xr.c b/source/blender/windowmanager/intern/wm_xr.c
index db4d306217e..200606211e5 100644
--- a/source/blender/windowmanager/intern/wm_xr.c
+++ b/source/blender/windowmanager/intern/wm_xr.c
@@ -141,7 +141,6 @@ static void wm_xr_session_free_data(wmSurface *surface)
 {
   wmXrSurfaceData *data = surface->customdata;
 
-  WM_opengl_context_dispose(surface->ghost_ctx);
   if (surface->secondary_ghost_ctx) {
 #ifdef WIN32
     if (data->gpu_binding_type == GHOST_kXrGraphicsD3D11) {
@@ -150,6 +149,7 @@ static void wm_xr_session_free_data(wmSurface *surface)
 #endif
   }
   GPU_context_active_set(surface->gpu_ctx);
+  DRW_opengl_context_enable_ex(false);
   if (data->viewport) {
     GPU_viewport_clear_from_offscreen(data->viewport);
     GPU_viewport_free(data->viewport);
@@ -157,7 +157,7 @@ static void wm_xr_session_free_data(wmSurface *surface)
   if (data->offscreen) {
     GPU_offscreen_free(data->offscreen);
   }
-  GPU_context_discard(surface->gpu_ctx);
+  DRW_opengl_context_disable_ex(false);
 
   MEM_freeN(surface->customdata);
 
@@ -173,7 +173,6 @@ static wmSurface *wm_xr_session_surface_create(wmWindowManager *wm, unsigned int
 
   wmSurface *surface = MEM_callocN(sizeof(*surface), __func__);
   wmXrSurfaceData *data = MEM_callocN(sizeof(*data), "XrSurfaceData");
-  unsigned int default_fb;
 
 #ifndef WIN32
   BLI_assert(gpu_binding_type == GHOST_kXrGraphicsOpenGL);
@@ -185,10 +184,8 @@ static wmSurface *wm_xr_session_surface_create(wmWindowManager *wm, unsigned int
   data->gpu_binding_type = gpu_binding_type;
   surface->customdata = data;
 
-  wm_window_clear_drawable(wm);
-  wm_surface_clear_drawable();
-  surface->ghost_ctx = WM_opengl_context_create();
-  WM_opengl_context_activate(surface->ghost_ctx);
+  surface->ghost_ctx = DRW_opengl_context_get();
+  DRW_opengl_context_enable();
 
   switch (gpu_binding_type) {
     case GHOST_kXrGraphicsOpenGL:
@@ -200,14 +197,9 @@ static wmSurface *wm_xr_session_surface_create(wmWindowManager *wm, unsigned int
 #endif
   }
 
-  default_fb = GHOST_GetContextDefaultOpenGLFramebuffer(surface->ghost_ctx);
-  surface->gpu_ctx = GPU_context_create(default_fb);
-
-  wm_surface_set_drawable(surface, false);
-  GHOST_SwapContextBuffers(surface->ghost_ctx);
-  GPU_state_init();
+  surface->gpu_ctx = DRW_gpu_context_get();
 
-  wm_surface_clear_drawable();
+  DRW_opengl_context_disable();
 
   g_xr_surface = surface;
 
@@ -254,6 +246,7 @@ static bool wm_xr_session_surface_offscreen_ensure(const GHOST_XrDrawViewInfo *d
     return true;
   }
 
+  DRW_opengl_context_enable();
   if (surface_data->offscreen) {
     GPU_viewport_clear_from_offscreen(surface_data->viewport);
     GPU_viewport_free(surface_data->viewport);
@@ -269,6 +262,7 @@ static bool wm_xr_session_surface_offscreen_ensure(const GHOST_XrDrawViewInfo *d
     GPU_offscreen_free(surface_data->offscreen);
     failure = true;
   }
+  DRW_opengl_context_disable();
 
   if (failure) {
     fprintf(stderr, "%s: failed to get buffer, %s\n", __func__, err_out);
@@ -294,15 +288,14 @@ static GHOST_ContextHandle wm_xr_draw_view(const GHOST_XrDrawViewInfo *draw_view
 
   wm_xr_draw_matrices_create(CTX_data_scene(C), draw_view, clip_start, clip_end, viewmat, winmat);
 
-  DRW_opengl_context_enable();
   if (!wm_xr_session_surface_offscreen_ensure(draw_view)) {
     return NULL;
   }
-  DRW_opengl_context_disable();
 
   offscreen = surface_data->offscreen;
   viewport = surface_data->viewport;
   GPU_viewport_bind(viewport, &rect);
+  glClear(GL_DEPTH_BUFFER_BIT);
 
   BKE_screen_view3d_shading_init(&shading);
   ED_view3d_draw_offscreen_simple(CTX_data_depsgraph(C),
@@ -325,18 +318,12 @@ static GHOST_ContextHandle wm_xr_draw_view(const GHOST_XrDrawViewInfo *draw_view
                                   offscreen,
                                   viewport);
 
-  /* Blit from the DRW context into the offscreen surface context. Would be good to avoid this.
-   * Idea: Allow passing custom offscreen context to DRW? */
-  //  GHOST_ContextBlitOpenGLOffscreenContext(
-  //      g_xr_surface->ghost_ctx, DRW_opengl_context_get(), draw_view->width, draw_view->height);
-
-  GPU_viewport_unbind(viewport);
   GPU_framebuffer_restore();
 
   GPUTexture *texture = GPU_offscreen_color_texture(offscreen);
 
-  WM_opengl_context_activate(g_xr_surface->ghost_ctx);
   wm_draw_offscreen_texture_parameters(offscreen);
+  GPU_depth_test(false);
 
   wmViewport(&rect);
   GPU_viewport_draw_to_screen(viewport, &rect);
@@ -346,6 +333,7 @@ static GHOST_ContextHandle wm_xr_draw_view(const GHOST_XrDrawViewInfo *draw_view
     wm_draw_upside_down(draw_view->width, draw_view->height);
     GPU_texture_unbind(texture);
   }
+  GPU_viewport_unbind(viewport);
 
   return g_xr_surface->ghost_ctx;
 }