DarkRoom/core/dr-pipeline/src/lib.rs

//! The develop pipeline — operations, descriptors, and shader composition.
//!
//! # What this crate is
//!
//! An operation here is three things: a **descriptor** saying what its
//! parameters are, a **WGSL fragment** saying what it does to a colour, and
//! the **state** of its current settings. It is not a shader, not a pipeline,
//! and not a control — those belong to `dr-gpu` and `dr-ui` respectively.
//!
//! That split is what lets this crate have no GPU dependency at all: the
//! generated WGSL is a string, and everything about it can be tested without
//! a device (ARCH §6.5a).
//!
//! # Composable shaders
//!
//! The interesting property. Operations are separate in Rust but *fused* on
//! the GPU: [`operation::compose`] concatenates the enabled operations'
//! fragments into one compute shader, so an edit with three active
//! adjustments runs as one dispatch with one texture read and one write.
//!
//! An operation at neutral settings contributes nothing — no code, no
//! uniform, no branch. The shader for a given op-set compiles once and is
//! cached by [`operation::ComposedShader::structure_hash`], which covers the
//! operations and their order but not their values; moving a slider uploads
//! uniforms and reuses the pipeline.
//!
//! # Where this sits
//!
//! Input is the demosaiced texture from `dr-gpu`: linear, scene-referred,
//! camera colour space. Working in linear light is what makes exposure a
//! single multiply and white balance a per-channel scale; on gamma-encoded
//! data neither would be physically meaningful (ARCH §5.2).

pub mod descriptor;
pub mod framing;
pub mod graph;
pub mod lens;
pub mod operation;
pub mod ops;
pub mod sidecar;

pub use descriptor::{
    Facet, LocalizedKey, OpDescriptor, OpId, ParamDescriptor, ParamId, ParamKind, Presentation,
    Scale, Unit, WidgetKind,
};
pub use framing::{CropRect, Framing};
pub use graph::{EditGraph, OpCapability, ParamCapability};
pub use lens::{compose_warps, ComposedWarp, Warp};
pub use operation::{
    compose, compose_with_framing, Affects, ComposedShader, Helper, Operation, Uniform,
    RESERVED_UNIFORM_FIELDS,
};
pub use sidecar::{Sidecar, Version};

#[cfg(test)]
mod tests {
    use super::*;

    /// Every operation in the default chain, activated.
    ///
    /// Parameters are moved away from their defaults by differing amounts,
    /// scaled by position. A uniform nudge is not enough: the tone curve's
    /// neutral is a *relationship* between its parameters rather than a set
    /// of values, so shifting every point by the same amount slides it along
    /// the identity diagonal and leaves the operation correctly inactive.
    /// Varying the step breaks that symmetry, as any real edit would.
    fn fully_active() -> EditGraph {
        let mut g = EditGraph::default_chain();
        for desc in g.descriptors() {
            for (i, p) in desc.params.iter().enumerate() {
                let v = match p.kind {
                    ParamKind::Scalar { min, max, .. } => {
                        // A fraction that differs per parameter, so no two
                        // move in lockstep.
                        let fraction = 0.15 + 0.05 * (i % 4) as f32;
                        let step = (max - min) * fraction;
                        if p.default + step <= max {
                            p.default + step
                        } else {
                            p.default - step
                        }
                    }
                    ParamKind::Bool => 1.0 - p.default,
                };
                g.set_param(desc.id, p.id, v);
            }
        }
        g
    }

    #[test]
    fn every_operation_can_be_activated_together() {
        let g = fully_active();
        assert!(!g.is_neutral());
        let shader = g.compose();
        // Counted against the chain rather than a literal, so adding an
        // operation does not require editing this test.
        assert_eq!(
            shader.source.matches("---- ").count(),
            g.descriptors().len(),
            "every operation in the chain should appear"
        );
    }

    #[test]
    fn the_full_chain_generates_a_well_formed_uniform_block() {
        let shader = fully_active().compose();
        assert_eq!(
            shader.uniforms.len() % 4,
            0,
            "the uniform block must be 16-byte aligned"
        );
        assert!(shader.uniforms.iter().all(|v| v.is_finite()));
    }

    #[test]
    fn no_operation_declares_a_duplicate_id() {
        // Two operations sharing an id would collide in the generated
        // uniform struct and produce a shader that does not compile.
        let g = EditGraph::default_chain();
        let mut ids: Vec<&str> = g.descriptors().iter().map(|d| d.id.0).collect();
        let before = ids.len();
        ids.sort_unstable();
        ids.dedup();
        assert_eq!(before, ids.len(), "operation ids must be unique");
    }

    #[test]
    fn no_operation_declares_a_duplicate_parameter() {
        for desc in EditGraph::default_chain().descriptors() {
            let mut ids: Vec<&str> = desc.params.iter().map(|p| p.id.0).collect();
            let before = ids.len();
            ids.sort_unstable();
            ids.dedup();
            assert_eq!(before, ids.len(), "{} has a duplicate parameter", desc.id);
        }
    }

    #[test]
    fn every_default_is_within_its_declared_range() {
        // A default outside its own range would mean a fresh image opens
        // with a value the UI cannot represent.
        for desc in EditGraph::default_chain().descriptors() {
            for p in desc.params {
                assert_eq!(
                    p.clamp(p.default),
                    p.default,
                    "{}.{} default {} is outside its range",
                    desc.id,
                    p.id,
                    p.default
                );
            }
        }
    }

    #[test]
    fn defaults_leave_every_operation_inactive() {
        // The invariant behind "opening an image shows the image": every
        // operation must read its own default as neutral.
        let g = EditGraph::default_chain();
        for desc in g.descriptors() {
            for p in desc.params {
                assert_eq!(
                    g.param(desc.id, p.id),
                    Some(p.default),
                    "{}.{} does not start at its default",
                    desc.id,
                    p.id
                );
            }
        }
        assert!(g.is_neutral());
    }

    #[test]
    fn generated_uniform_names_are_valid_wgsl_identifiers() {
        let shader = fully_active().compose();

        // Only the `struct Params` block. Scanning the whole source picks up
        // helper *signatures* such as `fn contrast_curve(x: f32, ...)`, whose
        // parameters are not uniform declarations at all.
        let body = shader
            .source
            .split_once("struct Params {")
            .expect("a uniform struct is always generated")
            .1
            .split_once('}')
            .expect("the struct is closed")
            .0;

        let mut checked = 0;
        for line in body.lines() {
            let trimmed = line.trim();
            if trimmed.starts_with("//") {
                continue;
            }
            let Some((name, _)) = trimmed.split_once(':') else {
                continue;
            };
            let name = name.trim();
            assert!(
                !name.is_empty()
                    && name.chars().all(|c| c.is_ascii_alphanumeric() || c == '_')
                    && !name.starts_with(|c: char| c.is_ascii_digit()),
                "{name} is not a valid WGSL identifier"
            );
            checked += 1;
        }
        assert!(checked > 0, "the struct should declare fields");
    }

    #[test]
    fn no_fragment_declares_a_wgsl_reserved_keyword() {
        // Caught the hard way: `let target = ...` in the contrast fragment
        // failed to compile with "name `target` is a reserved keyword", and
        // the error pointed at generated source rather than at the operation
        // that wrote it. Checking here names the culprit directly.
        //
        // Not the full reserved list — the ones a colour operation would
        // plausibly reach for.
        const RESERVED: &[&str] = &[
            "target",
            "sample",
            "filter",
            "texture",
            "buffer",
            "binding",
            "const",
            "enum",
            "mat",
            "vec",
            "ptr",
            "ref",
            "shared",
            "static",
            "typedef",
            "union",
            "unless",
            "handle",
            "layout",
            "packed",
            "premerge",
            "regardless",
            "typedef",
            "active",
            "do",
            "enum",
            "input",
            "output",
            "private",
            "resource",
            "restrict",
            "self",
            "std",
            "where",
        ];

        let g = EditGraph::default_chain();
        for cap in g.capabilities() {
            // Activate the whole operation so its fragment is emitted.
            let mut probe = EditGraph::default_chain();
            for p in &cap.params {
                if let ParamKind::Scalar { max, .. } = p.kind {
                    probe.set_param(cap.id, p.id, max * 0.5);
                }
            }
            let source = probe.compose().source;

            for keyword in RESERVED {
                let declaration = format!("let {keyword} ");
                let var_declaration = format!("var {keyword} ");
                assert!(
                    !source.contains(&declaration) && !source.contains(&var_declaration),
                    "{} declares `{keyword}`, which is a WGSL reserved keyword",
                    cap.id
                );
            }
        }
    }

    #[test]
    fn a_full_chain_declares_each_helper_once() {
        // Six of the seven operations want `luminance`. A duplicate function
        // definition fails to compile, so this is the property that keeps
        // helper sharing safe as operations are added.
        let source = fully_active().compose().source;
        for helper in ["luminance", "tone_position", "colour_saturation"] {
            let count = source.matches(&format!("fn {helper}(")).count();
            assert!(count <= 1, "{helper} declared {count} times");
        }
    }
}