Metal: Compile MTLLibrary on demand when pipeline is created
#103185
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This changes the default shader loading strategy, implemented in the Metal driver, to compile the `MTLLibrary` on demand when the pipeline is created, which reduces cold startup time on IPHONE target OSs. Normally, the `MTLLibrary` is compiled from Metal source asynchronously when Godot calls `RenderingDeviceDriverMetal::shader_create_from_bytecode`; however, this changes this behaviour on mobile platforms to do it on demand when the pipeline is created, as noted in godotengine#96052, Godot will ask to create many more shaders from bytecode than are initially required. Mobile OSs like iOS are limited to compiling to shader libraries concurrently, which results in a significant bottleneck. This is not the default for macOS, as it can concurrently compile many shaders at once, resulting in faster startup times for the Godot editor.
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Closes #103006
This changes the default shader loading strategy for mobile Apple platforms, implemented in the Metal driver, to compile the
MTLLibraryon demand when the pipeline is created. This reduces cold startup time on IPHONE target OSs (iOS, tvOS and visionOS).Normally, the
MTLLibraryis compiled from Metal source asynchronously when Godot callsRenderingDeviceDriverMetal::shader_create_from_bytecode; however, this changes this behaviour on mobile platforms to do it on demand when the pipeline is created. As noted in #96052, Godot will ask to create many more shaders from bytecode than are initially required. Mobile OSs like iOS are limited to compiling two shader libraries concurrently, which results in a significant bottleneck.This is not the default for macOS, as it can concurrently compile many shaders at once, resulting in faster startup times for the Godot editor.