Blender: Add command line argument to switch gpu backends.

Add command line argument to switch gpu backend. Add `--gpu-backend` option to
override the gpu backend selected by Blender.

Values for this option that will be available in releases for now are:
* opengl: Force blender to select OpenGL backend.

During development and depending on compile options additional values can exist:
* metal: Force Blender to select Metal backend.

When this option isn't provided the internal logic for GPU backend selection will be used.
Note that this is at the time of writing the same as always selecting the opengl backend.

Reviewed By: fclem, brecht, MichaelPW

Differential Revision: https://developer.blender.org/D16297

7 files changed, 94 insertions, 9 deletions

diff --git a/source/blender/gpu/GPU_context.h b/source/blender/gpu/GPU_context.h
index b59ea9e55d2..ac82774039a 100644
--- a/source/blender/gpu/GPU_context.h
+++ b/source/blender/gpu/GPU_context.h
@@ -21,6 +21,8 @@ extern "C" {
  * automatically initializes the back-end, and #GPU_context_discard frees it when there
  * are no more contexts. */
 bool GPU_backend_supported(void);
+void GPU_backend_type_selection_set(const eGPUBackendType backend);
+eGPUBackendType GPU_backend_type_selection_get(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 48d7b2019c5..f6b88c4231c 100644
--- a/source/blender/gpu/intern/gpu_context.cc
+++ b/source/blender/gpu/intern/gpu_context.cc
@@ -223,9 +223,19 @@ void GPU_render_step()
 /* NOTE: To enable Metal API, we need to temporarily change this to `GPU_BACKEND_METAL`.
  * Until a global switch is added, Metal also needs to be enabled in GHOST_ContextCGL:
  * `m_useMetalForRendering = true`. */
-static const eGPUBackendType g_backend_type = GPU_BACKEND_OPENGL;
+static eGPUBackendType g_backend_type = GPU_BACKEND_OPENGL;
 static GPUBackend *g_backend = nullptr;
 
+void GPU_backend_type_selection_set(const eGPUBackendType backend)
+{
+  g_backend_type = backend;
+}
+
+eGPUBackendType GPU_backend_type_selection_get()
+{
+  return g_backend_type;
+}
+
 bool GPU_backend_supported(void)
 {
   switch (g_backend_type) {
diff --git a/source/blender/gpu/intern/gpu_shader_builder.cc b/source/blender/gpu/intern/gpu_shader_builder.cc
index 3aa2963ecd0..9a67ddde5e6 100644
--- a/source/blender/gpu/intern/gpu_shader_builder.cc
+++ b/source/blender/gpu/intern/gpu_shader_builder.cc
@@ -15,6 +15,8 @@
 #include "GPU_init_exit.h"
 #include "gpu_shader_create_info_private.hh"
 
+#include "BLI_vector.hh"
+
 #include "CLG_log.h"
 
 namespace blender::gpu::shader_builder {
@@ -41,6 +43,22 @@ void ShaderBuilder::init()
   CLG_init();
 
   GHOST_GLSettings glSettings = {0};
+  switch (GPU_backend_type_selection_get()) {
+    case GPU_BACKEND_OPENGL:
+      glSettings.context_type = GHOST_kDrawingContextTypeOpenGL;
+      break;
+
+#ifdef WITH_METAL_BACKEND
+    case GPU_BACKEND_METAL:
+      glSettings.context_type = GHOST_kDrawingContextTypeMetal;
+      break;
+#endif
+
+    default:
+      BLI_assert_unreachable();
+      break;
+  }
+
   ghost_system_ = GHOST_CreateSystem();
   ghost_context_ = GHOST_CreateOpenGLContext(ghost_system_, glSettings);
   GHOST_ActivateOpenGLContext(ghost_context_);
@@ -73,13 +91,32 @@ int main(int argc, const char *argv[])
 
   int exit_code = 0;
 
-  blender::gpu::shader_builder::ShaderBuilder builder;
-  builder.init();
-  if (!builder.bake_create_infos()) {
-    exit_code = 1;
+  struct NamedBackend {
+    std::string name;
+    eGPUBackendType backend;
+  };
+
+  blender::Vector<NamedBackend> backends_to_validate;
+  backends_to_validate.append({"OpenGL", GPU_BACKEND_OPENGL});
+#ifdef WITH_METAL_BACKEND
+  backends_to_validate.append({"Metal", GPU_BACKEND_METAL});
+#endif
+  for (NamedBackend &backend : backends_to_validate) {
+    GPU_backend_type_selection_set(backend.backend);
+    if (!GPU_backend_supported()) {
+      printf("%s isn't supported on this platform. Shader compilation is skipped\n",
+             backend.name.c_str());
+      continue;
+    }
+    blender::gpu::shader_builder::ShaderBuilder builder;
+    builder.init();
+    if (!builder.bake_create_infos()) {
+      printf("Shader compilation failed for %s backend\n", backend.name.c_str());
+      exit_code = 1;
+    }
+    builder.exit();
+    exit(exit_code);
   }
-  builder.exit();
-  exit(exit_code);
 
   return exit_code;
 }
diff --git a/source/blender/gpu/intern/gpu_shader_builder_stubs.cc b/source/blender/gpu/intern/gpu_shader_builder_stubs.cc
index 7a06ede5c6d..65bda7ba858 100644
--- a/source/blender/gpu/intern/gpu_shader_builder_stubs.cc
+++ b/source/blender/gpu/intern/gpu_shader_builder_stubs.cc
@@ -46,6 +46,15 @@ void IMB_freeImBuf(ImBuf * /*ibuf*/)
   BLI_assert_unreachable();
 }
 
+struct ImBuf *IMB_allocImBuf(unsigned int /*x*/,
+                             unsigned int /*y*/,
+                             unsigned char /*planes*/,
+                             unsigned int /*flags*/)
+{
+  BLI_assert_unreachable();
+  return nullptr;
+}
+
 /** \} */
 
 /* -------------------------------------------------------------------- */
diff --git a/source/blender/windowmanager/intern/wm_playanim.c b/source/blender/windowmanager/intern/wm_playanim.c
index bf793ee41a0..3e5399a6f56 100644
--- a/source/blender/windowmanager/intern/wm_playanim.c
+++ b/source/blender/windowmanager/intern/wm_playanim.c
@@ -59,6 +59,8 @@
 
 #include "DEG_depsgraph.h"
 
+#include "wm_window_private.h"
+
 #include "WM_api.h" /* only for WM_main_playanim */
 
 #ifdef WITH_AUDASPACE
@@ -1340,6 +1342,8 @@ static bool ghost_event_proc(GHOST_EventHandle evt, GHOST_TUserDataPtr ps_void)
 static void playanim_window_open(const char *title, int posx, int posy, int sizex, int sizey)
 {
   GHOST_GLSettings glsettings = {0};
+  const eGPUBackendType gpu_backend = GPU_backend_type_selection_get();
+  glsettings.context_type = wm_ghost_drawing_context_type(gpu_backend);
   uint32_t scr_w, scr_h;
 
   GHOST_GetMainDisplayDimensions(g_WS.ghost_system, &scr_w, &scr_h);
@@ -1356,7 +1360,6 @@ static void playanim_window_open(const char *title, int posx, int posy, int size
                                          /* Could optionally start full-screen. */
                                          GHOST_kWindowStateNormal,
                                          false,
-                                         GHOST_kDrawingContextTypeOpenGL,
                                          glsettings);
 }
 
diff --git a/source/blender/windowmanager/intern/wm_window.c b/source/blender/windowmanager/intern/wm_window.c
index b1b13390932..6b925b23dcb 100644
--- a/source/blender/windowmanager/intern/wm_window.c
+++ b/source/blender/windowmanager/intern/wm_window.c
@@ -556,6 +556,9 @@ static void wm_window_ghostwindow_add(wmWindowManager *wm,
     glSettings.flags |= GHOST_glDebugContext;
   }
 
+  eGPUBackendType gpu_backend = GPU_backend_type_selection_get();
+  glSettings.context_type = wm_ghost_drawing_context_type(gpu_backend);
+
   int scr_w, scr_h;
   wm_get_desktopsize(&scr_w, &scr_h);
   int posy = (scr_h - win->posy - win->sizey);
@@ -573,7 +576,6 @@ static void wm_window_ghostwindow_add(wmWindowManager *wm,
                                                    win->sizey,
                                                    (GHOST_TWindowState)win->windowstate,
                                                    is_dialog,
-                                                   GHOST_kDrawingContextTypeOpenGL,
                                                    glSettings);
 
   if (ghostwin) {
@@ -1615,6 +1617,23 @@ const char *WM_ghost_backend(void)
 #endif
 }
 
+GHOST_TDrawingContextType wm_ghost_drawing_context_type(const eGPUBackendType gpu_backend)
+{
+  switch (gpu_backend) {
+    case GPU_BACKEND_NONE:
+      return GHOST_kDrawingContextTypeNone;
+    case GPU_BACKEND_ANY:
+    case GPU_BACKEND_OPENGL:
+      return GHOST_kDrawingContextTypeOpenGL;
+#ifdef WITH_METAL_BACKEND
+    case GPU_BACKEND_METAL:
+      return GHOST_kDrawingContextTypeMetal;
+#endif
+  }
+  BLI_assert_unreachable();
+  return GHOST_kDrawingContextTypeNone;
+}
+
 /** \} */
 
 /* -------------------------------------------------------------------- */
diff --git a/source/blender/windowmanager/intern/wm_window_private.h b/source/blender/windowmanager/intern/wm_window_private.h
index f68d4e3e693..dad3e749817 100644
--- a/source/blender/windowmanager/intern/wm_window_private.h
+++ b/source/blender/windowmanager/intern/wm_window_private.h
@@ -7,8 +7,11 @@
 #pragma once
 
 #include "BLI_sys_types.h"
+
 #include "GHOST_Types.h"
 
+#include "GPU_context.h"
+
 /* *************** Message box *************** */
 /* `WM_ghost_show_message_box` is implemented in `wm_windows.c` it is
  * defined here as it was implemented to be used for showing
@@ -21,3 +24,5 @@ void WM_ghost_show_message_box(const char *title,
                                const char *continue_label,
                                const char *link,
                                GHOST_DialogOptions dialog_options);
+
+GHOST_TDrawingContextType wm_ghost_drawing_context_type(const eGPUBackendType gpu_backend);