Windows: Fall back to D3D12 if Vulkan is not supported and vice versa

[kus04e4ek]

• Fixes: Windows PC without Vulkan or OpenGL should default to Direct3D12 #94760.

Similar approach to rendering/gl_compatibility/fallback_to_angle, rendering/gl_compatibility/fallback_to_gles and rendering/gl_compatibility/fallback_to_native.
Can be tested with this (with this Godot will always try to fall back to another driver):

diff --git a/platform/windows/display_server_windows.cpp b/platform/windows/display_server_windows.cpp
index b8fcab64177..36cf4e10bd3 100644
--- a/platform/windows/display_server_windows.cpp
+++ b/platform/windows/display_server_windows.cpp
@@ -5928,7 +5928,7 @@ DisplayServerWindows::DisplayServerWindows(const String &p_rendering_driver, Win
 #endif
 
 	if (rendering_context) {
-		if (rendering_context->initialize() != OK) {
+		if (true) {
 			bool failed = true;
 #if defined(VULKAN_ENABLED)
 			bool fallback_to_vulkan = GLOBAL_GET("rendering/rendering_device/vulkan/fallback_to_vulkan");

[Calinou]

Note that the original issue also refers to PCs without OpenGL support (i.e. ARM laptops without the compatibility pack installed). Falling back to Direct3D 12 on those would imply using a different rendering method – and therefore different visuals – unless ANGLE is used. I expect ANGLE to be quite a bit slower than a native D3D12 implementation.

Either way, this might be worth its own proposal so you can choose which rendering methods can fall back to other ones (e.g. falling back to Compatibility if Forward+/Mobile is not supported, or vice versa).

[kus04e4ek]

Not quite sure I understood your comment correctly.

Note that the original issue also refers to PCs without OpenGL support (i.e. ARM laptops without the compatibility pack installed). Falling back to Direct3D 12 on those would imply using a different rendering method.

This PR doesn't do it, it will only fall back to Direct3D 12 from Vulkan. If native OpenGL is not supported Godot already falls back to ANGLE on Windows.

Either way, this might be worth its own proposal so you can choose which rendering methods can fall back to other ones (e.g. falling back to Compatibility if Forward+/Mobile is not supported, or vice versa).

Agree, I think this PR is ok as is for 4.3 cause Godot already falls back to different rendering drivers within the same rendering method, this can be improved in future versions.

[bruvzg]

Note that the original issue also refers to PCs without OpenGL support (i.e. ARM laptops without the compatibility pack installed). Falling back to Direct3D 12 on those would imply using a different rendering method – and therefore different visuals – unless ANGLE is used. I expect ANGLE to be quite a bit slower than a native D3D12 implementation.

Currently, we aren't even trying to load native GL on ARM64 if engine was compiled with ANGLE, it's switching to ANGLE (over D3D11) automatically.

[bruvzg]

Wouldn't it be clearer to have it named rendering/rendering_device/d3d12/fallback_to_vulkan and rendering/rendering_device/vulkan/fallback_to_d3d12, since it's Direct3D falling back to Vulkan and vice versa? Or have it directly under the rendering/rendering_device/

[kus04e4ek]

Moved to rendering/rendering_device/, but I don't have a strong opinion

[akien-mga]

Thanks!