GPUBackend: Add new GPUBackend object to manage GL object allocations

This just set a global object responsible for allocating new objects
in a thread safe way without needing any GPUContext bound to this
thread.

This also introduce the GLContext which will contain all the GL related
functions for the current context.

4 files changed, 131 insertions, 48 deletions

diff --git a/source/blender/gpu/intern/gpu_backend.hh b/source/blender/gpu/intern/gpu_backend.hh
new file mode 100644
index 00000000000..24f592f214f
--- /dev/null
+++ b/source/blender/gpu/intern/gpu_backend.hh
@@ -0,0 +1,37 @@
+/*
+ * This program is free software; you can redistribute it and/or
+ * modify it under the terms of the GNU General Public License
+ * as published by the Free Software Foundation; either version 2
+ * of the License, or (at your option) any later version.
+ *
+ * This program is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+ * GNU General Public License for more details.
+ *
+ * You should have received a copy of the GNU General Public License
+ * along with this program; if not, write to the Free Software Foundation,
+ * Inc., 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301, USA.
+ *
+ * Copyright 2020, Blender Foundation.
+ * All rights reserved.
+ */
+
+/** \file
+ * \ingroup gpu
+ *
+ * GPUBackend derived class contain allocators that do not need a context bound.
+ * The backend is init at startup and is accessible using GPU_backend_get() */
+
+#pragma once
+
+struct GPUContext;
+
+class GPUBackend {
+ public:
+  virtual ~GPUBackend(){};
+
+  virtual GPUContext *context_alloc(void *ghost_window) = 0;
+};
+
+GPUBackend *gpu_backend_get(void);
diff --git a/source/blender/gpu/intern/gpu_context.cc b/source/blender/gpu/intern/gpu_context.cc
index c3c0863f6cd..9707c32cede 100644
--- a/source/blender/gpu/intern/gpu_context.cc
+++ b/source/blender/gpu/intern/gpu_context.cc
@@ -28,6 +28,9 @@
  * - free can be called from any thread
  */
 
+/* TODO Create cmake option. */
+#define WITH_OPENGL_BACKEND 1
+
 #include "BLI_assert.h"
 #include "BLI_utildefines.h"
 
@@ -36,63 +39,25 @@
 
 #include "GHOST_C-api.h"
 
+#include "gpu_backend.hh"
 #include "gpu_batch_private.h"
 #include "gpu_context_private.h"
 #include "gpu_matrix_private.h"
 
+#ifdef WITH_OPENGL_BACKEND
+#  include "gl_backend.hh"
+#  include "gl_context.hh"
+#endif
+
 #include <mutex>
-#include <pthread.h>
-#include <string.h>
-#include <unordered_set>
 #include <vector>
 
-#if TRUST_NO_ONE
-#  if 0
-extern "C" {
-extern int BLI_thread_is_main(void); /* Blender-specific function */
-}
-
-static bool thread_is_main()
-{
-  /* "main" here means the GL context's thread */
-  return BLI_thread_is_main();
-}
-#  endif
-#endif
-
 static std::vector<GLuint> orphaned_buffer_ids;
 static std::vector<GLuint> orphaned_texture_ids;
 
 static std::mutex orphans_mutex;
 static std::mutex main_context_mutex;
 
-struct GPUContext {
-  GLuint default_vao;
-  GLuint default_framebuffer;
-  GPUFrameBuffer *current_fbo;
-  std::unordered_set<GPUBatch *> batches; /* Batches that have VAOs from this context */
-#ifdef DEBUG
-  std::unordered_set<GPUFrameBuffer *>
-      framebuffers; /* Framebuffers that have FBO from this context */
-#endif
-  struct GPUMatrixState *matrix_state;
-  std::vector<GLuint> orphaned_vertarray_ids;
-  std::vector<GLuint> orphaned_framebuffer_ids;
-  std::mutex orphans_mutex; /* todo: try spinlock instead */
-#if TRUST_NO_ONE
-  pthread_t thread; /* Thread on which this context is active. */
-  bool thread_is_used;
-#endif
-
-  GPUContext()
-  {
-#if TRUST_NO_ONE
-    thread_is_used = false;
-#endif
-    current_fbo = 0;
-  }
-};
-
 static thread_local GPUContext *active_ctx = NULL;
 
 static void orphans_add(GPUContext *ctx, std::vector<GLuint> *orphan_list, GLuint id)
@@ -142,8 +107,12 @@ static void orphans_clear(GPUContext *ctx)
 
 GPUContext *GPU_context_create(void *ghost_window)
 {
-  /* BLI_assert(thread_is_main()); */
-  GPUContext *ctx = new GPUContext;
+  if (gpu_backend_get() == NULL) {
+    /* TODO move where it make sense. */
+    GPU_backend_init(GPU_BACKEND_OPENGL);
+  }
+
+  GPUContext *ctx = gpu_backend_get()->context_alloc(ghost_window);
   glGenVertexArrays(1, &ctx->default_vao);
   if (ghost_window != NULL) {
     ctx->default_framebuffer = GHOST_GetDefaultOpenGLFramebuffer((GHOST_WindowHandle)ghost_window);
@@ -364,3 +333,37 @@ void GPU_context_main_unlock(void)
 {
   main_context_mutex.unlock();
 }
+
+/* -------------------------------------------------------------------- */
+/** \name Backend selection
+ * \{ */
+
+static GPUBackend *g_backend;
+
+void GPU_backend_init(eGPUBackendType backend_type)
+{
+  BLI_assert(g_backend == NULL);
+
+  switch (backend_type) {
+#if WITH_OPENGL_BACKEND
+    case GPU_BACKEND_OPENGL:
+      g_backend = new GLBackend;
+      break;
+#endif
+    default:
+      BLI_assert(0);
+      break;
+  }
+}
+
+void GPU_backend_exit(void)
+{
+  delete g_backend;
+}
+
+GPUBackend *gpu_backend_get(void)
+{
+  return g_backend;
+}
+
+/** \} */
diff --git a/source/blender/gpu/intern/gpu_context_private.h b/source/blender/gpu/intern/gpu_context_private.h
index 08fbefe3b3f..374a05bc25f 100644
--- a/source/blender/gpu/intern/gpu_context_private.h
+++ b/source/blender/gpu/intern/gpu_context_private.h
@@ -27,12 +27,52 @@
 
 #include "GPU_context.h"
 
+/* TODO cleanup this ifdef */
 #ifdef __cplusplus
-extern "C" {
-#endif
+
+#  include <mutex>
+#  include <pthread.h>
+#  include <string.h>
+#  include <unordered_set>
+#  include <vector>
 
 struct GPUFrameBuffer;
 
+struct GPUContext {
+  GLuint default_vao;
+  GLuint default_framebuffer;
+  GPUFrameBuffer *current_fbo;
+  std::unordered_set<GPUBatch *> batches; /* Batches that have VAOs from this context */
+#  ifdef DEBUG
+  std::unordered_set<GPUFrameBuffer *>
+      framebuffers; /* Framebuffers that have FBO from this context */
+#  endif
+  struct GPUMatrixState *matrix_state;
+  std::vector<GLuint> orphaned_vertarray_ids;
+  std::vector<GLuint> orphaned_framebuffer_ids;
+  std::mutex orphans_mutex; /* todo: try spinlock instead */
+#  if TRUST_NO_ONE
+  pthread_t thread; /* Thread on which this context is active. */
+  bool thread_is_used;
+#  endif
+
+  GPUContext()
+  {
+#  if TRUST_NO_ONE
+    thread_is_used = false;
+#  endif
+    current_fbo = 0;
+  };
+
+  virtual ~GPUContext(){};
+};
+
+#endif
+
+#ifdef __cplusplus
+extern "C" {
+#endif
+
 GLuint GPU_vao_default(void);
 GLuint GPU_framebuffer_default(void);
 
diff --git a/source/blender/gpu/intern/gpu_init_exit.c b/source/blender/gpu/intern/gpu_init_exit.c
index c5061ec9ba3..462a1d395c2 100644
--- a/source/blender/gpu/intern/gpu_init_exit.c
+++ b/source/blender/gpu/intern/gpu_init_exit.c
@@ -26,6 +26,7 @@
 #include "BLI_sys_types.h"
 #include "GPU_batch.h"
 #include "GPU_buffers.h"
+#include "GPU_context.h"
 #include "GPU_immediate.h"
 
 #include "intern/gpu_codegen.h"
@@ -92,6 +93,8 @@ void GPU_exit(void)
   gpu_extensions_exit();
   gpu_platform_exit(); /* must come last */
 
+  GPU_backend_exit();
+
   initialized = false;
 }