DRW: Move GPU context lock out of the DST variable.

This doesnt remove the locking but isolate the `GPUContext`
lock to oustide the `DrawManager` class.

This has no functional change.

Pull Request: https://projects.blender.org/blender/blender/pulls/135189

source/blender/draw/intern/DRW_render.hh

@@ -81,6 +81,7 @@ struct DrawEngineType {
 };
 
 /* Shaders */
+/** IMPORTANT: Modify the currently bound context. */
 void DRW_shader_init();
 void DRW_shader_exit();
 

source/blender/draw/intern/draw_manager_c.cc

@@ -111,6 +111,26 @@
 
 static CLG_LogRef LOG = {"draw.manager"};
 
+/* -------------------------------------------------------------------- */
+/** \name Settings
+ *
+ * A global GPUContext is used for rendering every viewports (even on different windows).
+ * This is because some resources cannot be shared between contexts (GPUFramebuffers, GPUBatch).
+ * \{ */
+
+/** Unique ghost context used by Viewports. */
+static void *system_gpu_context = nullptr;
+/** GPUContext associated to the system_gpu_context. */
+static GPUContext *blender_gpu_context = nullptr;
+/**
+ * GPUContext cannot be used concurrently. This isn't required at the moment since viewports
+ * aren't rendered in parallel but this could happen in the future. The old implementation of DRW
+ * was also locking so this is a bit of a preventive measure. Could eventually be removed.
+ */
+static TicketMutex *system_gpu_context_mutex = nullptr;
+
+/** \} */
+
 /** Render State: No persistent data between draw calls. */
 DRWManager DST = {nullptr};
 
@@ -121,7 +141,7 @@ static struct {
 
 static void drw_state_prepare_clean_for_draw(DRWManager *dst)
 {
-  memset(dst, 0x0, offsetof(DRWManager, system_gpu_context));
+  memset(dst, 0x0, offsetof(DRWManager, debug));
 }
 
 /* This function is used to reset draw manager to a state
@@ -131,7 +151,7 @@ static void drw_state_prepare_clean_for_draw(DRWManager *dst)
 #ifndef NDEBUG
 static void drw_state_ensure_not_reused(DRWManager *dst)
 {
-  memset(dst, 0xff, offsetof(DRWManager, system_gpu_context));
+  memset(dst, 0xff, offsetof(DRWManager, debug));
 }
 #endif /* !NDEBUG */
 
@@ -1128,7 +1148,7 @@ void DRW_notify_view_update(const DRWUpdateContext *update_ctx)
    * Check for recursive lock which can deadlock. This should not
    * happen, but in case there is a bug where depsgraph update is called
    * during drawing we try not to hang Blender. */
-  if (!BLI_ticket_mutex_lock_check_recursive(DST.system_gpu_context_mutex)) {
+  if (!BLI_ticket_mutex_lock_check_recursive(system_gpu_context_mutex)) {
     CLOG_ERROR(&LOG, "GPU context already bound");
     BLI_assert_unreachable();
     return;
@@ -1168,7 +1188,7 @@ void DRW_notify_view_update(const DRWUpdateContext *update_ctx)
 
   drw_manager_exit(&DST);
 
-  BLI_ticket_mutex_unlock(DST.system_gpu_context_mutex);
+  BLI_ticket_mutex_unlock(system_gpu_context_mutex);
 }
 
 /* update a viewport which belongs to a GPUOffscreen */
@@ -2815,7 +2835,7 @@ void DRW_engines_free()
   using namespace blender::draw;
   drw_registered_engines_free();
 
-  if (DST.system_gpu_context == nullptr) {
+  if (system_gpu_context == nullptr) {
     /* Nothing has been setup. Nothing to clear.
      * Otherwise, DRW_gpu_context_enable can
      * create a context in background mode. (see #62355) */
@@ -2837,7 +2857,7 @@ void DRW_engines_free()
 
 void DRW_render_context_enable(Render *render)
 {
-  if (G.background && DST.system_gpu_context == nullptr) {
+  if (G.background && system_gpu_context == nullptr) {
     WM_init_gpu();
   }
 
@@ -2895,57 +2915,61 @@ void DRW_render_context_disable(Render *render)
 
 void DRW_gpu_context_create()
 {
-  BLI_assert(DST.system_gpu_context == nullptr); /* Ensure it's called once */
+  BLI_assert(system_gpu_context == nullptr); /* Ensure it's called once */
 
-  DST.system_gpu_context_mutex = BLI_ticket_mutex_alloc();
+  /* Setup compilation context. Called first as it changes the active GPUContext. */
-  /* This changes the active context. */
-  DST.system_gpu_context = WM_system_gpu_context_create();
-  WM_system_gpu_context_activate(DST.system_gpu_context);
-  /* Be sure to create blender_gpu_context too. */
-  DST.blender_gpu_context = GPU_context_create(nullptr, DST.system_gpu_context);
-  /* Setup compilation context. */
   DRW_shader_init();
-  /* Activate the window's context afterwards. */
+
+  system_gpu_context_mutex = BLI_ticket_mutex_alloc();
+  /* This changes the active context. */
+  system_gpu_context = WM_system_gpu_context_create();
+  WM_system_gpu_context_activate(system_gpu_context);
+  /* Be sure to create blender_gpu_context too. */
+  blender_gpu_context = GPU_context_create(nullptr, system_gpu_context);
+  /* Some part of the code assumes no context is left bound. */
+  GPU_context_active_set(nullptr);
+  WM_system_gpu_context_release(system_gpu_context);
+  /* Activate the window's context if any. */
   wm_window_reset_drawable();
 }
 
 void DRW_gpu_context_destroy()
 {
   BLI_assert(BLI_thread_is_main());
-  if (DST.system_gpu_context != nullptr) {
+  if (system_gpu_context != nullptr) {
     DRW_shader_exit();
-    WM_system_gpu_context_activate(DST.system_gpu_context);
+    WM_system_gpu_context_activate(system_gpu_context);
-    GPU_context_active_set(DST.blender_gpu_context);
+    GPU_context_active_set(blender_gpu_context);
-    GPU_context_discard(DST.blender_gpu_context);
+    GPU_context_discard(blender_gpu_context);
-    WM_system_gpu_context_dispose(DST.system_gpu_context);
+    WM_system_gpu_context_dispose(system_gpu_context);
-    BLI_ticket_mutex_free(DST.system_gpu_context_mutex);
+    BLI_ticket_mutex_free(system_gpu_context_mutex);
   }
 }
 
 void DRW_gpu_context_enable_ex(bool /*restore*/)
 {
-  if (DST.system_gpu_context != nullptr) {
+  if (system_gpu_context != nullptr) {
     /* IMPORTANT: We don't support immediate mode in render mode!
      * This shall remain in effect until immediate mode supports
      * multiple threads. */
-    BLI_ticket_mutex_lock(DST.system_gpu_context_mutex);
+    BLI_ticket_mutex_lock(system_gpu_context_mutex);
     GPU_render_begin();
-    WM_system_gpu_context_activate(DST.system_gpu_context);
+    WM_system_gpu_context_activate(system_gpu_context);
-    GPU_context_active_set(DST.blender_gpu_context);
+    GPU_context_active_set(blender_gpu_context);
-    GPU_context_begin_frame(DST.blender_gpu_context);
+    GPU_context_begin_frame(blender_gpu_context);
   }
 }
 
 void DRW_gpu_context_disable_ex(bool restore)
 {
-  if (DST.system_gpu_context != nullptr) {
+  if (system_gpu_context != nullptr) {
-    GPU_context_end_frame(DST.blender_gpu_context);
+    GPU_context_end_frame(blender_gpu_context);
 
     if (BLI_thread_is_main() && restore) {
       wm_window_reset_drawable();
     }
     else {
-      WM_system_gpu_context_release(DST.system_gpu_context);
+      WM_system_gpu_context_release(system_gpu_context);
       GPU_context_active_set(nullptr);
     }
 
@@ -2953,7 +2977,7 @@ void DRW_gpu_context_disable_ex(bool restore)
      * called outside of an existing render loop. */
     GPU_render_end();
 
-    BLI_ticket_mutex_unlock(DST.system_gpu_context_mutex);
+    BLI_ticket_mutex_unlock(system_gpu_context_mutex);
   }
 }
 
@@ -2961,7 +2985,7 @@ void DRW_gpu_context_enable()
 {
   /* TODO: should be replace by a more elegant alternative. */
 
-  if (G.background && DST.system_gpu_context == nullptr) {
+  if (G.background && system_gpu_context == nullptr) {
     WM_init_gpu();
   }
   DRW_gpu_context_enable_ex(true);
@@ -2977,16 +3001,14 @@ void DRW_system_gpu_render_context_enable(void *re_system_gpu_context)
   /* If thread is main you should use DRW_gpu_context_enable(). */
   BLI_assert(!BLI_thread_is_main());
 
-  /* TODO: get rid of the blocking. Only here because of the static global DST. */
+  BLI_ticket_mutex_lock(system_gpu_context_mutex);
-  BLI_ticket_mutex_lock(DST.system_gpu_context_mutex);
   WM_system_gpu_context_activate(re_system_gpu_context);
 }
 
 void DRW_system_gpu_render_context_disable(void *re_system_gpu_context)
 {
   WM_system_gpu_context_release(re_system_gpu_context);
-  /* TODO: get rid of the blocking. */
+  BLI_ticket_mutex_unlock(system_gpu_context_mutex);
-  BLI_ticket_mutex_unlock(DST.system_gpu_context_mutex);
 }
 
 void DRW_blender_gpu_render_context_enable(void *re_gpu_context)
@@ -3018,28 +3040,28 @@ void *DRW_system_gpu_context_get()
    * have to work from the main thread, which is tricky to get working too. The preferable solution
    * would be using a separate thread for VR drawing where a single context can stay active. */
 
-  return DST.system_gpu_context;
+  return system_gpu_context;
 }
 
 void *DRW_xr_blender_gpu_context_get()
 {
   /* XXX: See comment on #DRW_system_gpu_context_get(). */
 
-  return DST.blender_gpu_context;
+  return blender_gpu_context;
 }
 
 void DRW_xr_drawing_begin()
 {
   /* XXX: See comment on #DRW_system_gpu_context_get(). */
 
-  BLI_ticket_mutex_lock(DST.system_gpu_context_mutex);
+  BLI_ticket_mutex_lock(system_gpu_context_mutex);
 }
 
 void DRW_xr_drawing_end()
 {
   /* XXX: See comment on #DRW_system_gpu_context_get(). */
 
-  BLI_ticket_mutex_unlock(DST.system_gpu_context_mutex);
+  BLI_ticket_mutex_unlock(system_gpu_context_mutex);
 }
 
 #endif
@@ -3095,7 +3117,7 @@ bool DRW_gpu_context_release()
     return false;
   }
 
-  if (GPU_context_active_get() != DST.blender_gpu_context) {
+  if (GPU_context_active_get() != blender_gpu_context) {
     /* Context release is requested from the outside of the draw manager main draw loop, indicate
      * this to the `DRW_gpu_context_activate()` so that it restores drawable of the window.
      */
@@ -3103,7 +3125,7 @@ bool DRW_gpu_context_release()
   }
 
   GPU_context_active_set(nullptr);
-  WM_system_gpu_context_release(DST.system_gpu_context);
+  WM_system_gpu_context_release(system_gpu_context);
 
   return true;
 }
@@ -3115,8 +3137,8 @@ void DRW_gpu_context_activate(bool drw_state)
   }
 
   if (drw_state) {
-    WM_system_gpu_context_activate(DST.system_gpu_context);
+    WM_system_gpu_context_activate(system_gpu_context);
-    GPU_context_active_set(DST.blender_gpu_context);
+    GPU_context_active_set(blender_gpu_context);
   }
   else {
     wm_window_reset_drawable();

source/blender/draw/intern/draw_manager_c.hh

@@ -139,14 +139,6 @@ struct DRWManager {
 
   /* ---------- Nothing after this point is cleared after use ----------- */
 
-  /* system_gpu_context serves as the offset for clearing only
-   * the top portion of the struct so DO NOT MOVE IT! */
-  /** Unique ghost context used by the draw manager. */
-  void *system_gpu_context;
-  GPUContext *blender_gpu_context;
-  /** Mutex to lock the drw manager and avoid concurrent context usage. */
-  TicketMutex *system_gpu_context_mutex;
-
   DRWDebugModule *debug;
 };
 

source/blender/draw/intern/draw_manager_shader.cc

@@ -193,9 +193,10 @@ void DRW_shader_init()
   compiler_data().system_gpu_context = WM_system_gpu_context_create();
   compiler_data().blender_gpu_context = GPU_context_create(nullptr,
                                                            compiler_data().system_gpu_context);
+
+  /* Some part of the code assumes no context is left bound. */
   GPU_context_active_set(nullptr);
-  WM_system_gpu_context_activate(DST.system_gpu_context);
+  WM_system_gpu_context_release(compiler_data().system_gpu_context);
-  GPU_context_active_set(DST.blender_gpu_context);
 
   BLI_threadpool_init(&compilation_threadpool(), drw_deferred_shader_compilation_exec, 1);
   BLI_threadpool_insert(&compilation_threadpool(), nullptr);