API to accept and use precompiled shader

[hajimehoshi]

Operating System

• Windows
• macOS
• Linux
• FreeBSD
• OpenBSD
• Android
• iOS
• Nintendo Switch
• PlayStation 5
• Xbox
• Web Browsers

What feature would you like to be added?

On consoles, compiling shaders is possible but takes long (Xbox), or, is probably impossible (PS5) 😢. We might need a tool to precompile shader and APIs to use them...

Why is this needed?

For some special environments where dynamic compiling shaders is difficult.

[f9x0]

Hello. Consider adding an API to use your shaders.
Without a doubt, this feature will be for experienced developers and will open the way to the world of shaders. Naga, wgsl and other community tools. I like Kage, but it's good to have an alternative..

[hajimehoshi]

I'm afraid this suggestion is not for enabling other languages than Kage

[hajimehoshi]

To minimize an impact of the existing APIs, I suggest this API:

// AddPrecompiledShader adds a pair of a shader source and a shader binary.
// When a new shader is created by NewShader,
// Ebitengine tries to seek the pair that has the same shader source.
// If there is such a pair, Ebitengine uses a registered shader binary for the same shader source instead of compiling it.
//
// AddPrecompiledShader is useful to shoten the shader compile time, or even necessary in an environment
// where you cannot compile a shader on the fly.
func AddPrecompiledShader(kageShaderSource []byte, nativeShaderBinary []byte, graphicsLibrary GraphicsLibrary) error

EDIT: Hmm, how can we treat vertex shader?

[hajimehoshi]

OpenGL: It is impossible to precompile shaders. AddPrecompiledShader should always return an error.

DirectX: A native shader binary is the result of D3DCompile. This function returns ID3DBlob, and this can be converted to a byte slice, and be created via D3DCreateBlob. A vertex shader and a pixel shader are separated.

Metal: A native shader binary is a .metallib format. This can be used at makeLibrary for NSData. See also https://developer.apple.com/documentation/metal/shader_libraries/building_a_shader_library_by_precompiling_source_files. A vertex shader and a fragment shader are NOT separated. So, Ebitengine would have to expose the binary for a vertex shader? Hmm.

[hajimehoshi]

Instead of exposing the the vertex shader, would this work?

func CompileShaderToNativeSource(kageShaderSource []byte, graphicsLibrary GraphicsLibrary) ([]byte, error)

// Compiling a native source to a native binary is a developer's responsibility.

func AddPrecompiledShader(kageShaderSource []byte, nativeShaderBinary []byte, graphicsLibrary GraphicsLibrary) error

[hajimehoshi]

Compiling and using a shader

in a pseudo Go-like code.

OpenGL

vertex_shader_source, fragment_shader_source = glsl.Compile(ir)
vertex_shader = glNewShader(vertex_shader_source)
fragment_shader = glNewShader(fragment_shader_source)
program = glNewProgram(vertex_shader, fragmen_shader, array_buffer_layout_names)

Metal

src = metal.Compile(ir)
lib = MakeLibrary(src)
vertex_function = MakeFunction(lib, vertex_name)
fragment_function = MakeFunction(lib, fragment_name)

See also:

• https://developer.apple.com/documentation/metal/shader_libraries/building_a_shader_library_by_precompiling_source_files?language=objc

DirectX

vertex_shader_source, pixel_shader_source, offsets = hlsl.Compile(ir)
vertex_blob = D3DCompile(vertex_shader, name, ...)
pixel_blob = D3DCompile(pixel_shader, name, ...)

See also:

• https://learn.microsoft.com/en-us/windows/win32/direct3dtools/dx-graphics-tools-fxc-using
• https://learn.microsoft.com/en-us/windows/win32/direct3dhlsl/dx-graphics-hlsl-part1
• https://learn.microsoft.com/en-us/windows/win32/direct3d11/how-to--compile-a-shader

Proposal (TBD)

As there are various ways to compile and use shaders in different environments, the precompilation APIs should be separate for each environment unfortunately.

package shaderprecomp

func BuiltinShaderSources() [][]byte
 
func CompileToHLSL(kageSource []byte) (vertex []byte, pixel []byte, err error)

func RegisterDirectXShaderBlobs(kageSource []byte, vertexBlob []byte, pixelBlob []byte)

func CompileToMSL(kageSource []byte) ([]byte, error)

func RegisterMetalShaderLibrary(kageSource []byte, library []byte)

[hajimehoshi]

The final API is like this

package shaderprecomp

type ShaderSource struct {
    // ...
}
func NewShaderSource([]byte) (*ShaderSource, error)
func (s *ShaderSource) ID() ShaderSourceID

type ShaderSourceID [16]byte
func (s *ShaderSourceID) String() string

func AppendBuiltinShaderSources(sources []*ShaderSource) []*ShaderSource
 
func CompileToHLSL(vertexWriter, pixelWriter io.Writer, kageSource *ShaderSource) error

func RegisterFXCs(id ShaderSourceID, vertexFXC []byte, pixelFXC []byte)

func CompileToMSL(w io.Writer, kageSource *ShaderSource) error

func RegisterMetalLibrary(id ShaderSourceID, library []byte)

[hajimehoshi]

With #2984, I realized some considerations:

• Builtin shaders don't have to or should not be exposed.
• The shader complation processes like what the examples/shaderprecomp does can be provided by this package, and CompileTo* might able to be hidden.

Thus, until I decide a better API design, I'd like to retract the package once. I might postpone the milestone for release.