4 files changed, 37 insertions, 31 deletions

diff --git a/source/blender/gpu/GPU_context.h b/source/blender/gpu/GPU_context.h
index c81296093a1..9d92ea2cad9 100644
--- a/source/blender/gpu/GPU_context.h
+++ b/source/blender/gpu/GPU_context.h
@@ -17,14 +17,10 @@
 extern "C" {
 #endif
 
-/* GPU backends abstract the differences between different APIs. These must be
- * initialized before creating contexts, and deleted after the last context is
- * discarded. GPU_context_create automatically initializes a backend if none
- * exists yet. */
-bool GPU_backend_init_once(void);
-void GPU_backend_exit(void);
-bool GPU_backend_supported(eGPUBackendType type);
-
+/* GPU backends abstract the differences between different APIs. GPU_context_create
+ * automatically initializes the backend, and GPU_context_discard frees it when there
+ * are no more contexts. */
+bool GPU_backend_supported(void);
 eGPUBackendType GPU_backend_get_type(void);
 
 /** Opaque type hiding blender::gpu::Context. */
diff --git a/source/blender/gpu/intern/gpu_context.cc b/source/blender/gpu/intern/gpu_context.cc
index 5ae020e45a4..20d9208a199 100644
--- a/source/blender/gpu/intern/gpu_context.cc
+++ b/source/blender/gpu/intern/gpu_context.cc
@@ -44,6 +44,12 @@ using namespace blender::gpu;
 
 static thread_local Context *active_ctx = nullptr;
 
+static std::mutex backend_users_mutex;
+static int num_backend_users = 0;
+
+static void gpu_backend_create();
+static void gpu_backend_discard();
+
 /* -------------------------------------------------------------------- */
 /** \name gpu::Context methods
  * \{ */
@@ -86,7 +92,14 @@ Context *Context::get()
 
 GPUContext *GPU_context_create(void *ghost_window)
 {
-  GPU_backend_init_once();
+  {
+    std::scoped_lock lock(backend_users_mutex);
+    if (num_backend_users == 0) {
+      /* Automatically create backend when first context is created. */
+      gpu_backend_create();
+    }
+    num_backend_users++;
+  }
 
   Context *ctx = GPUBackend::get()->context_alloc(ghost_window);
 
@@ -99,6 +112,16 @@ void GPU_context_discard(GPUContext *ctx_)
   Context *ctx = unwrap(ctx_);
   delete ctx;
   active_ctx = nullptr;
+
+  {
+    std::scoped_lock lock(backend_users_mutex);
+    num_backend_users--;
+    BLI_assert(num_backend_users >= 0);
+    if (num_backend_users == 0) {
+      /* Discard backend when last context is discarded. */
+      gpu_backend_discard();
+    }
+  }
 }
 
 void GPU_context_active_set(GPUContext *ctx_)
@@ -189,11 +212,12 @@ void GPU_render_step()
 /** \name Backend selection
  * \{ */
 
+static const eGPUBackendType g_backend_type = GPU_BACKEND_OPENGL;
 static GPUBackend *g_backend = nullptr;
 
-bool GPU_backend_supported(eGPUBackendType type)
+bool GPU_backend_supported(void)
 {
-  switch (type) {
+  switch (g_backend_type) {
     case GPU_BACKEND_OPENGL:
 #ifdef WITH_OPENGL_BACKEND
       return true;
@@ -212,21 +236,12 @@ bool GPU_backend_supported(eGPUBackendType type)
   }
 }
 
-bool GPU_backend_init_once()
+static void gpu_backend_create()
 {
-  if (GPUBackend::get() != nullptr) {
-    return true;
-  }
-
-  const eGPUBackendType backend_type = GPU_BACKEND_OPENGL;
-  if (!GPU_backend_supported(backend_type)) {
-    return false;
-  }
+  BLI_assert(g_backend == nullptr);
+  BLI_assert(GPU_backend_supported(g_backend_type));
 
-  static std::mutex backend_init_mutex;
-  std::scoped_lock lock(backend_init_mutex);
-
-  switch (backend_type) {
+  switch (g_backend_type) {
 #ifdef WITH_OPENGL_BACKEND
     case GPU_BACKEND_OPENGL:
       g_backend = new GLBackend;
@@ -241,8 +256,6 @@ bool GPU_backend_init_once()
       BLI_assert(0);
       break;
   }
-
-  return true;
 }
 
 void gpu_backend_delete_resources()
@@ -251,7 +264,7 @@ void gpu_backend_delete_resources()
   g_backend->delete_resources();
 }
 
-void GPU_backend_exit()
+void gpu_backend_discard()
 {
   /* TODO: assert no resource left. */
   delete g_backend;
diff --git a/source/blender/gpu/tests/gpu_testing.cc b/source/blender/gpu/tests/gpu_testing.cc
index 5a2ad893360..224a9afcf59 100644
--- a/source/blender/gpu/tests/gpu_testing.cc
+++ b/source/blender/gpu/tests/gpu_testing.cc
@@ -17,7 +17,6 @@ void GPUTest::SetUp()
   GHOST_GLSettings glSettings = {0};
   CLG_init();
   ghost_system = GHOST_CreateSystem();
-  GPU_backend_init_once();
   ghost_context = GHOST_CreateOpenGLContext(ghost_system, glSettings);
   GHOST_ActivateOpenGLContext(ghost_context);
   context = GPU_context_create(nullptr);
@@ -29,7 +28,6 @@ void GPUTest::TearDown()
   GPU_exit();
   GPU_context_discard(context);
   GHOST_DisposeOpenGLContext(ghost_system, ghost_context);
-  GPU_backend_exit();
   GHOST_DisposeSystem(ghost_system);
   CLG_exit();
 }
diff --git a/source/blender/windowmanager/intern/wm_init_exit.c b/source/blender/windowmanager/intern/wm_init_exit.c
index 7324abfd096..7f5ec77e16d 100644
--- a/source/blender/windowmanager/intern/wm_init_exit.c
+++ b/source/blender/windowmanager/intern/wm_init_exit.c
@@ -169,7 +169,7 @@ void WM_init_opengl(void)
     wm_ghost_init(NULL);
   }
 
-  if (!GPU_backend_init_once()) {
+  if (!GPU_backend_supported()) {
     return;
   }
 
@@ -613,7 +613,6 @@ void WM_exit_ex(bContext *C, const bool do_python)
   else {
     UI_exit();
   }
-  GPU_backend_exit();
 
   BKE_blender_userdef_data_free(&U, false);