Fix T77564: VSE (and compositor background) lost stereoscopy preview

Issue introduced on fe045b2b77.

Since the stereoscopy compositing (anaglyph, ...) is only done for
viewports the VSE preview and compositor need to use viewports.

Reviewed by: dfelinto

Differential Revision: https://developer.blender.org/D8472

source/blender/editors/space_node/node_draw.c

@@ -52,6 +52,7 @@
 #include "GPU_immediate_util.h"
 #include "GPU_matrix.h"
 #include "GPU_state.h"
+#include "GPU_viewport.h"
 
 #include "WM_api.h"
 #include "WM_types.h"
@@ -1755,6 +1756,12 @@ void drawnodespace(const bContext *C, ARegion *region)
   SpaceNode *snode = CTX_wm_space_node(C);
   View2D *v2d = &region->v2d;
 
+  /* Setup offscreen buffers. */
+  GPUViewport *viewport = WM_draw_region_get_viewport(region);
+
+  GPUFrameBuffer *framebuffer_overlay = GPU_viewport_framebuffer_overlay_get(viewport);
+  GPU_framebuffer_bind_no_srgb(framebuffer_overlay);
+
   UI_ThemeClearColor(TH_BACK);
   GPU_clear(GPU_COLOR_BIT);
 

source/blender/editors/space_sequencer/sequencer_draw.c

@@ -56,6 +56,7 @@
 #include "GPU_matrix.h"
 #include "GPU_state.h"
 #include "GPU_vertex_buffer.h"
+#include "GPU_viewport.h"
 
 #include "ED_anim_api.h"
 #include "ED_gpencil.h"
@@ -1537,7 +1538,7 @@ static void sequencer_preview_clear(void)
   float col[3];
 
   UI_GetThemeColor3fv(TH_SEQ_PREVIEW, col);
-  GPU_clear_color(col[0], col[1], col[2], 0.0);
+  GPU_clear_color(col[0], col[1], col[2], 1.0f);
   GPU_clear(GPU_COLOR_BIT);
 }
 
@@ -1780,6 +1781,12 @@ void sequencer_draw_preview(const bContext *C,
     return;
   }
 
+  /* Setup offscreen buffers. */
+  GPUViewport *viewport = WM_draw_region_get_viewport(region);
+
+  GPUFrameBuffer *framebuffer_overlay = GPU_viewport_framebuffer_overlay_get(viewport);
+  GPU_framebuffer_bind_no_srgb(framebuffer_overlay);
+
   /* Setup view. */
   sequencer_display_size(scene, viewrect);
   UI_view2d_totRect_set(v2d, viewrect[0] + 0.5f, viewrect[1] + 0.5f);
@@ -1798,6 +1805,9 @@ void sequencer_draw_preview(const bContext *C,
   ibuf = sequencer_ibuf_get(
       bmain, depsgraph, scene, sseq, cfra, frame_ofs, names[sseq->multiview_eye]);
 
+  /* sequencer_ibuf_get can call GPU_framebuffer_bind. So disable srgb framebuffer again. */
+  GPU_framebuffer_bind_no_srgb(framebuffer_overlay);
+
   if (ibuf) {
     scope = sequencer_get_scope(scene, sseq, ibuf, draw_backdrop);
 

source/blender/gpu/GPU_framebuffer.h

@@ -61,6 +61,7 @@ typedef struct GPUOffScreen GPUOffScreen;
 GPUFrameBuffer *GPU_framebuffer_create(void);
 void GPU_framebuffer_free(GPUFrameBuffer *fb);
 void GPU_framebuffer_bind(GPUFrameBuffer *fb);
+void GPU_framebuffer_bind_no_srgb(GPUFrameBuffer *fb);
 void GPU_framebuffer_restore(void);
 
 bool GPU_framebuffer_bound(GPUFrameBuffer *fb);

source/blender/gpu/intern/gpu_framebuffer.cc

@@ -555,6 +555,18 @@ void GPU_framebuffer_bind(GPUFrameBuffer *fb)
   glViewport(0, 0, fb->width, fb->height);
 }
 
+/* Workaround for binding a srgb framebuffer without doing the srgb transform. */
+void GPU_framebuffer_bind_no_srgb(GPUFrameBuffer *fb)
+{
+  GPU_framebuffer_bind(fb);
+
+  glDisable(GL_FRAMEBUFFER_SRGB);
+
+  GPUTexture *first_target = fb->attachments[GPU_FB_COLOR_ATTACHMENT0].tex;
+  const bool is_srgb_target = (first_target && (GPU_texture_format(first_target) == GPU_SRGB8_A8));
+  GPU_shader_set_framebuffer_srgb_target(!is_srgb_target);
+}
+
 void GPU_framebuffer_restore(void)
 {
   if (GPU_framebuffer_active_get() != NULL) {

source/blender/windowmanager/intern/wm_draw.c

@@ -307,7 +307,9 @@ static void wm_region_test_xr_do_draw(const wmWindowManager *wm,
 
 static bool wm_region_use_viewport_by_type(short space_type, short region_type)
 {
-  return (ELEM(space_type, SPACE_VIEW3D, SPACE_IMAGE) && region_type == RGN_TYPE_WINDOW);
+  return (ELEM(space_type, SPACE_VIEW3D, SPACE_IMAGE, SPACE_NODE) &&
+          region_type == RGN_TYPE_WINDOW) ||
+         ((space_type == SPACE_SEQ) && region_type == RGN_TYPE_PREVIEW);
 }
 
 bool WM_region_use_viewport(ScrArea *area, ARegion *region)