Merge PR #1238

# Conflicts:
#	crates/pipeline/src/spots.rs
#	crates/ui-egui/src/panels/edit.rs
#	docs/parity-checklist.md

crates/pipeline/src/lib.rs

@@ -471,6 +471,10 @@ pub fn settings_for<'a>(s: &'a DevelopSettings, req: &RenderRequest) -> std::bor
 /// Long edge (pixels) of the small HDR render [`hdr_histogram`] measures.
 pub const HDR_HISTOGRAM_EDGE: usize = 384;
 
+/// Long edge of the render that gives a slider drag its live HDR histogram (drafts have none: a
+/// second render per tick would slow them down), run beside the drafts by the UI.
+pub const HDR_HISTOGRAM_DRAG_EDGE: usize = 192;
+
 /// The histogram of an HDR edit's HDR rendition for a preview request `req`: a small float HDR
 /// render of the same framing ([`HDR_HISTOGRAM_EDGE`]), binned with SDR on the left half and the
 /// whole HDR range ([`Hdr::MAX_EV_LIMIT`](lightcraft_develop::Hdr::MAX_EV_LIMIT) stops above SDR

crates/ui-egui/src/panels/edit.rs

@@ -6,11 +6,13 @@ use egui::{Align2, Color32, Pos2, Rect, RichText, Sense, Stroke, pos2, vec2};
 use lightcraft_catalog::PhotoId;
 use lightcraft_develop::{ControlSpec, DevelopSettings, Section, Track, WbMode, controls};
 use lightcraft_geom::Point;
+use lightcraft_raster::Histogram;
 use serde_json::{Value, json};
 
 use crate::LightcraftApp;
 use crate::icons::{Icon, paint};
 use crate::render::Slot;
+use crate::state::RightPanel;
 use crate::theme::Tokens;
 use crate::widgets::{BAND_COLORS, SliderOut, divider, flyout_row, hex, register, section_header, slider, text_button};
 
@@ -549,11 +551,42 @@ fn preview_histogram(app: &LightcraftApp, id: PhotoId) -> Option<lightcraft_rast
         .or_else(|| app.renderer.textures.get(&Slot::Thumb(id)).and_then(|t| t.histogram.clone()))
 }
 
+/// An HDR edit's histogram stays an HDR histogram: some renders carry only their 8-bit image's
+/// (a drag's drafts, a cached thumbnail or stand-in), and showing those would swap the panel to
+/// the SDR layout and back while a slider moves. Every render with HDR bins replaces the one kept for the photo, so
+/// the histogram still follows the edit live; an SDR edit shows what it gets.
+fn steady_hdr_histogram(ctx: &egui::Context, id: PhotoId, hdr_edit: bool, hist: Option<Histogram>) -> Option<Histogram> {
+    let key = egui::Id::new(("hdrHistogram", id));
+    match hist {
+        Some(h) if h.hdr.is_some() => {
+            ctx.data_mut(|d| d.insert_temp(key, h.clone()));
+            Some(h)
+        }
+        h if hdr_edit => ctx.data(|d| d.get_temp::<Histogram>(key)).or(h),
+        h => h,
+    }
+}
+
 fn histogram(app: &mut LightcraftApp, ui: &mut egui::Ui, id: PhotoId) {
     let t = Tokens::get(ui.ctx());
     let w = ui.available_width();
-    // the loupe render of this photo, else its thumbnail
-    let hist = preview_histogram(app, id);
+    let hdr_edit = app.session.develop_of(id).is_some_and(|d| d.hdr.enabled);
+    // a drag of an HDR edit: its drafts have no HDR histogram, so a small render beside them
+    // gives one (at its own pace: the drafts don't wait for it)
+    let interacting = app.session.interaction.is_some();
+    if interacting && hdr_edit {
+        let edge = lightcraft_pipeline::HDR_HISTOGRAM_DRAG_EDGE;
+        if let Some(job) = app.session.render_job(id, edge, edge, false, app.ui.right != RightPanel::Crop)
+            && app.renderer.live_hdr_histogram.as_ref().is_none_or(|l| l.1 != job.key)
+        {
+            app.renderer.request(Slot::HdrHistogram, job, 95);
+        }
+    }
+    let live = app.renderer.live_hdr_histogram.as_ref().filter(|l| interacting && l.0 == id).map(|l| l.2.clone());
+    // else the loupe render of this photo, else its thumbnail (grid view before the loupe has
+    // rendered it)
+    let hist = live.or_else(|| preview_histogram(app, id));
+    let hist = steady_hdr_histogram(ui.ctx(), id, hdr_edit, hist);
     // an HDR edit's histogram (`pipeline::hdr_histogram`) gets a colour bar and an SDR / HDR label
     // row under the plot
     let hdr = hist.as_ref().and_then(|h| h.hdr);
@@ -1664,3 +1697,29 @@ mod curve_histogram_tests {
         assert!(values.iter().any(|v| *v > 0.0));
     }
 }
+
+#[cfg(test)]
+mod tests {
+    use super::*;
+
+    #[test]
+    fn an_hdr_edit_keeps_its_hdr_histogram_through_8_bit_renders() {
+        let ctx = egui::Context::default();
+        let id = PhotoId(7);
+        let sdr = Histogram::of_hdr(&[], 5.0);
+        let sdr = Histogram { hdr: None, ..sdr };
+        let hdr = |v: f32| Histogram::of_hdr(&[[v, v, v]], 5.0);
+        // nothing kept yet: what arrives
+        assert_eq!(steady_hdr_histogram(&ctx, id, true, Some(sdr.clone())), Some(sdr.clone()));
+        assert_eq!(steady_hdr_histogram(&ctx, id, true, Some(hdr(2.0))), Some(hdr(2.0)));
+        // a cached thumbnail's 8-bit histogram (or none) doesn't swap the panel to SDR
+        assert_eq!(steady_hdr_histogram(&ctx, id, true, Some(sdr.clone())), Some(hdr(2.0)));
+        assert_eq!(steady_hdr_histogram(&ctx, id, true, None), Some(hdr(2.0)));
+        // the next HDR render replaces it: the histogram follows the slider
+        assert_eq!(steady_hdr_histogram(&ctx, id, true, Some(hdr(4.0))), Some(hdr(4.0)));
+        assert_eq!(steady_hdr_histogram(&ctx, id, true, Some(sdr.clone())), Some(hdr(4.0)));
+        // HDR turned off: the SDR histogram at once; other photos keep their own
+        assert_eq!(steady_hdr_histogram(&ctx, id, false, Some(sdr.clone())), Some(sdr.clone()));
+        assert_eq!(steady_hdr_histogram(&ctx, PhotoId(8), true, Some(sdr.clone())), Some(sdr));
+    }
+}

crates/ui-egui/src/render.rs

@@ -55,6 +55,9 @@ pub enum Slot {
     Import(u32),
     /// The second window's view of the active photo.
     Second,
+    /// A slider drag's live HDR histogram: a small full-quality render of an HDR edit, beside the
+    /// drafts (which have no HDR histogram), with no texture ([`Renderer::live_hdr_histogram`]).
+    HdrHistogram,
 }
 
 pub struct Tex {
@@ -187,6 +190,8 @@ pub struct Renderer {
     /// Slot → (key, priority) of the request in flight (queued or running).
     pending: HashMap<Slot, (u64, u32)>,
     pub textures: HashMap<Slot, Tex>,
+    /// The last [`Slot::HdrHistogram`] result: (photo, job key, histogram).
+    pub live_hdr_histogram: Option<(PhotoId, u64, Histogram)>,
     pub last_main_ms: f64,
     /// Jobs finished since start (for inspect/perf).
     pub completed: u64,
@@ -232,7 +237,7 @@ impl Slot {
     /// An interactive view of the open photo: slider drags redo only the stages they feed, and a
     /// draft that finishes late still replaces older pixels.
     pub fn is_view(self) -> bool {
-        matches!(self, Slot::Main | Slot::Region | Slot::RegionBefore | Slot::Before | Slot::Hover)
+        matches!(self, Slot::Main | Slot::Region | Slot::RegionBefore | Slot::Before | Slot::Hover | Slot::HdrHistogram)
     }
 }
 
@@ -263,6 +268,7 @@ impl Renderer {
             seq: 0,
             pending: HashMap::new(),
             textures: HashMap::new(),
+            live_hdr_histogram: None,
             last_main_ms: 0.0,
             completed: 0,
             keep_pixels: false,
@@ -752,6 +758,13 @@ impl Renderer {
             if matches!(slot, Slot::Prefetch(_)) {
                 continue;
             }
+            if slot == Slot::HdrHistogram {
+                if rendered.histogram.hdr.is_some() {
+                    self.live_hdr_histogram = Some((r.photo, r.key, rendered.histogram));
+                    changed = true;
+                }
+                continue;
+            }
             if let Slot::ThumbQuick(id) = slot {
                 if self.textures.contains_key(&Slot::Thumb(id)) {
                     continue; // the real thumbnail won the race
@@ -1278,6 +1291,33 @@ mod thumbnail_tests {
         assert!(!app.renderer.is_pending(Slot::Main));
     }
 
+    #[test]
+    fn a_drag_gets_its_live_hdr_histogram_beside_the_drafts() {
+        let (mut app, work, ctx) = fixture();
+        let mut jobs = Vec::new();
+        for exposure in [1.0, 2.0] {
+            let mut edit = lightcraft_develop::DevelopSettings::default();
+            edit.hdr.enabled = true;
+            edit.light.exposure = exposure;
+            app.session.catalog.apply(Op::SetDevelop { id: PhotoId(1), settings: Arc::new(edit), label: "drag".into(), edited: None }).unwrap();
+            let job = app.session.render_job(PhotoId(1), 32, 32, false, true).unwrap();
+            app.renderer.request(Slot::HdrHistogram, job, 95);
+            jobs.push(take_job(&work).1);
+        }
+        let keys: Vec<u64> = jobs.iter().map(|j| j.key).collect();
+        let mut jobs = jobs.into_iter();
+        let (first, last) = (jobs.next().unwrap(), jobs.next().unwrap());
+        // superseded while the drag goes on, it still lands: the histogram keeps moving
+        finish(&mut app, &work, &ctx, Slot::HdrHistogram, first.run());
+        let live = app.renderer.live_hdr_histogram.clone().expect("a live HDR histogram");
+        assert_eq!((live.0, live.1), (PhotoId(1), keys[0]));
+        assert!(live.2.hdr.is_some(), "HDR bins");
+        finish(&mut app, &work, &ctx, Slot::HdrHistogram, last.run());
+        assert_eq!(app.renderer.live_hdr_histogram.as_ref().map(|l| l.1), Some(keys[1]));
+        // only the histogram is kept: no texture
+        assert!(!app.renderer.textures.contains_key(&Slot::HdrHistogram));
+    }
+
     #[test]
     fn library_reset_rejects_old_job_even_when_photo_id_and_key_are_reused() {
         let (mut app, work, ctx) = fixture();

docs/parity-checklist.md

@@ -152,6 +152,8 @@ differences and missing bindings are in [ui-parity.md](ui-parity.md#shortcuts).
 | LR-VIEW-CLIPPING | Clipping indicators | P0 | ✅ | `cmd:view.clipping` | |
 | LR-VIEW-HISTOGRAM | Histogram | P0 | ✅ | `cmd:view.histogram`, `crates/ui-egui/src/panels/edit.rs`, `crates/pipeline/src/lib.rs` (`hdr_histogram`) | HDR edits: SDR on the left half, the HDR range (0 to 5 stops above SDR white, a fixed scale) on the right with the headroom limit marked; colour bar (white, or Visualize HDR range's colours when that is on) and SDR / HDR labels; no drag-to-adjust on the histogram |
 | LR-VIEW-HDR-DISPLAY | HDR display output | P2 | ⬜ | `apps/lightcraft/src/hdr_display.rs` (`choose`, `preferred_hdr_format`) | SDR/HDR decision (platform, surface format, OS headroom, `LIGHTCRAFT_HDR_DISPLAY=0`) is unit-tested and logged at start; always SDR today because eframe configures an 8-bit surface; no OS headroom query yet |
+| LR-VIEW-HISTOGRAM | Histogram | P0 | ✅ | `cmd:view.histogram`, `crates/ui-egui/src/panels/edit.rs`, `crates/pipeline/src/lib.rs` (`hdr_histogram`) | HDR edits: SDR on the left half, the HDR range (0 to 5 stops above SDR white, a fixed scale) on the right with the headroom limit marked; colour bar (white, or Visualize HDR range's colours when that is on) and SDR / HDR labels; it follows slider drags live (a small render beside the drafts, `Slot::HdrHistogram`) and never drops to the SDR layout mid-drag; no drag-to-adjust on the histogram |
+| LR-VIEW-HDR-DISPLAY | HDR display output | P2 | ⬜ | | |
 
 ## D. Search & filter (FILT)