Fix T99706: Crash rendering with headless builds

When rendering with headless builds, show an error instead of crashing.

Previously GPU_backend_init was called indirectly from
DRW_opengl_context_create, a new function is now called from the window
manager (GPU_backend_init_once), so it's possible to check if the GPU
has a back-end.

This also disables the `bgl` Python module when building WITH_HEADLESS.

Reviewed By: fclem

Ref D15463

3 files changed, 15 insertions, 5 deletions

diff --git a/source/blender/gpu/CMakeLists.txt b/source/blender/gpu/CMakeLists.txt
index 0cb92e02515..774f2a0f312 100644
--- a/source/blender/gpu/CMakeLists.txt
+++ b/source/blender/gpu/CMakeLists.txt
@@ -5,7 +5,7 @@
 # to more easily highlight code-paths in other libraries that need to be refactored,
 # bf_gpu is allowed to have opengl regardless of this option.
 
-if(NOT WITH_OPENGL AND NOT WITH_METAL_BACKEND)
+if(NOT WITH_OPENGL AND NOT WITH_METAL_BACKEND AND NOT WITH_HEADLESS)
   add_definitions(-DWITH_OPENGL)
 endif()
 
diff --git a/source/blender/gpu/GPU_context.h b/source/blender/gpu/GPU_context.h
index 1fcd94c48fc..b04a4422baa 100644
--- a/source/blender/gpu/GPU_context.h
+++ b/source/blender/gpu/GPU_context.h
@@ -17,6 +17,7 @@
 extern "C" {
 #endif
 
+bool GPU_backend_init_once(void);
 void GPU_backend_init(eGPUBackendType backend);
 void GPU_backend_exit(void);
 bool GPU_backend_supported(eGPUBackendType type);
diff --git a/source/blender/gpu/intern/gpu_context.cc b/source/blender/gpu/intern/gpu_context.cc
index 4a0a9ecc7f6..d3b208dc6f6 100644
--- a/source/blender/gpu/intern/gpu_context.cc
+++ b/source/blender/gpu/intern/gpu_context.cc
@@ -85,10 +85,7 @@ Context *Context::get()
 
 GPUContext *GPU_context_create(void *ghost_window)
 {
-  if (GPUBackend::get() == nullptr) {
-    /* TODO: move where it make sense. */
-    GPU_backend_init(GPU_BACKEND_OPENGL);
-  }
+  GPU_backend_init_once();
 
   Context *ctx = GPUBackend::get()->context_alloc(ghost_window);
 
@@ -214,6 +211,18 @@ bool GPU_backend_supported(eGPUBackendType type)
   }
 }
 
+bool GPU_backend_init_once()
+{
+  if (GPUBackend::get() == nullptr) {
+    if (!GPU_backend_supported(GPU_BACKEND_OPENGL)) {
+      return false;
+    }
+    /* TODO: move where it make sense. */
+    GPU_backend_init(GPU_BACKEND_OPENGL);
+  }
+  return true;
+}
+
 void GPU_backend_init(eGPUBackendType backend_type)
 {
   BLI_assert(g_backend == nullptr);