Shaders: runtime and shader node codegen (#2985)

* shader-rt: initial

* shader-rt: fix recursion when generating shader node

* shader-rt: replace gpu node's args and ret types with `Raster<GPU>`

* shader-rt: properly cfg out the gpu node

* shader-rt: fix `impl Context` in the wrong places

* shader-rt: disable gpu blend node, needs two images

* shader-rt: connect shader runtime

* shader-rt: pass WgpuExecutor by reference

* shader-rt: correct bindings with derpy arg buffer

* shader-rt: manual pipeline layout, fixing errors when bindings got DCE'd

* shader-rt: correct RT format, working invert gpu node

* shader-rt: cleanup codegen with common sym struct

* shader-rt: correct arg buffer handling

* shader-nodes feature: put shader nodes behind feature gate

* shader-nodes feature: rename any `gpu_node` to `shader-node`

* shaders-rt: fix wgpu label name

* shaders-rt: explain fullscreen_vertex coordinates with a drawing

node-graph/node-macro/src/shader_nodes/mod.rs

@@ -3,24 +3,38 @@ use crate::shader_nodes::per_pixel_adjust::PerPixelAdjust;
 use proc_macro2::{Ident, TokenStream};
 use quote::quote;
 use strum::VariantNames;
-use syn::Error;
 use syn::parse::{Parse, ParseStream};
+use syn::punctuated::Punctuated;
+use syn::{Error, Token};
 
 pub mod per_pixel_adjust;
 
 pub const STD_FEATURE_GATE: &str = "std";
+pub const SHADER_NODES_FEATURE_GATE: &str = "shader-nodes";
 
 pub fn modify_cfg(attributes: &NodeFnAttributes) -> TokenStream {
-	match (&attributes.cfg, &attributes.shader_node) {
-		(Some(cfg), Some(_)) => quote!(#[cfg(all(#cfg, feature = #STD_FEATURE_GATE))]),
-		(Some(cfg), None) => quote!(#[cfg(#cfg)]),
-		(None, Some(_)) => quote!(#[cfg(feature = #STD_FEATURE_GATE)]),
-		(None, None) => quote!(),
-	}
+	let feature_gate = match &attributes.shader_node {
+		// shader node cfg is done on the mod
+		Some(ShaderNodeType::ShaderNode) => quote!(),
+		Some(_) => quote!(feature = #STD_FEATURE_GATE),
+		None => quote!(),
+	};
+	let cfgs: Punctuated<_, Token![,]> = match &attributes.cfg {
+		None => [&feature_gate].into_iter().collect(),
+		Some(cfg) => [cfg, &feature_gate].into_iter().collect(),
+	};
+	quote!(#[cfg(all(#cfgs))])
 }
 
-#[derive(Debug, VariantNames)]
+#[derive(Debug, Clone, VariantNames)]
 pub(crate) enum ShaderNodeType {
+	/// Marker for this node being in a gpu node crate, but not having a gpu implementation. This is distinct from not
+	/// declaring `shader_node` at all, as it will wrap the CPU node with a `#[cfg(feature = "std")]` feature gate.
+	None,
+	/// Marker for this node being a generated gpu node implementation, that should not emit anything to prevent
+	/// recursively generating more gpu nodes. But it still counts as a gpu node and will get the
+	/// `#[cfg(feature = "std")]` feature gate around it's impl.
+	ShaderNode,
 	PerPixelAdjust(PerPixelAdjust),
 }
 
@@ -28,24 +42,37 @@ impl Parse for ShaderNodeType {
 	fn parse(input: ParseStream) -> syn::Result<Self> {
 		let ident: Ident = input.parse()?;
 		Ok(match ident.to_string().as_str() {
+			"None" => ShaderNodeType::None,
 			"PerPixelAdjust" => ShaderNodeType::PerPixelAdjust(PerPixelAdjust::parse(input)?),
 			_ => return Err(Error::new_spanned(&ident, format!("attr 'shader_node' must be one of {:?}", Self::VARIANTS))),
 		})
 	}
 }
 
-pub trait CodegenShaderEntryPoint {
-	fn codegen_shader_entry_point(&self, parsed: &ParsedNodeFn) -> syn::Result<TokenStream>;
+pub trait ShaderCodegen {
+	fn codegen(&self, parsed: &ParsedNodeFn) -> syn::Result<ShaderTokens>;
 }
 
-impl CodegenShaderEntryPoint for ShaderNodeType {
-	fn codegen_shader_entry_point(&self, parsed: &ParsedNodeFn) -> syn::Result<TokenStream> {
-		if parsed.is_async {
-			return Err(Error::new_spanned(&parsed.fn_name, "Shader nodes must not be async"));
+impl ShaderCodegen for ShaderNodeType {
+	fn codegen(&self, parsed: &ParsedNodeFn) -> syn::Result<ShaderTokens> {
+		match self {
+			ShaderNodeType::None | ShaderNodeType::ShaderNode => (),
+			_ => {
+				if parsed.is_async {
+					return Err(Error::new_spanned(&parsed.fn_name, "Shader nodes must not be async"));
+				}
+			}
 		}
 
 		match self {
-			ShaderNodeType::PerPixelAdjust(x) => x.codegen_shader_entry_point(parsed),
+			ShaderNodeType::None | ShaderNodeType::ShaderNode => Ok(ShaderTokens::default()),
+			ShaderNodeType::PerPixelAdjust(x) => x.codegen(parsed),
 		}
 	}
 }
+
+#[derive(Clone, Default)]
+pub struct ShaderTokens {
+	pub shader_entry_point: TokenStream,
+	pub gpu_node: TokenStream,
+}