region: a selection across monitors, stitched into one image

docs/test-checklist.md

@@ -147,6 +147,8 @@ image, a cancel brought the thumbnail back, and a swipe still dismissed it.
 - [ ] Each shot is a two-hit "ka-chunk" (macOS-like) with a metallic clatter that grows from shot 2; shots in quick succession play sounds 1 → 5 getting faster and brighter, then 6, 7, 6, 7 (a climbing bell arpeggio over a glide) rising endlessly; every shot about as loud; after a 5 s pause it starts at 1 again. `valw __combo-demo` plays the whole sequence for tuning.
 - [ ] `[sound] enabled = false`, `volume`, `combo_reset_secs` take effect; the toolbar's Play sound option overrides the config; no `pw-play` → no sound, capture still works (warning in the log).
 
+- [ ] Region across monitors: drag from the laptop up onto the monitor and back; each screen shows its part, the label shows the whole size on the screen under the pointer; Shift, Alt and Space work across the edge; the PNG is the whole rectangle, seams exact, parts over no screen transparent; the preview appears on the screen where you let go; a box on one screen is exactly as before.
+
 ### Known minors (deferred from the polish review)
 
 - Releasing Shift mid-drag only updates the rectangle on the next pointer motion.

src/main.rs

@@ -310,6 +310,10 @@ fn capture(mode: Mode, common: Common) -> Result<()> {
                     let source = frames[i].output.name.clone();
                     (vec![(frames[i].to_rgba(r), None)], 0, source)
                 }
+                region::Choice::Span(span, on) => {
+                    let source = frames[on].output.name.clone();
+                    (vec![(stitch::stitch(&frames, &span), None)], 0, source)
+                }
                 region::Choice::Window => {
                     drop(frames);
                     windowed = true;

src/region.rs

@@ -38,6 +38,9 @@ pub const NAMESPACE: &str = "valw-overlay";
 pub enum Choice {
     /// A rectangle in the frame of output `.0`.
     Region(usize, PixelRect),
+    /// A rectangle over several outputs (or past one's edge), with the
+    /// output the pointer was over at release (for the preview).
+    Span(selection::Span, usize),
     /// Space before dragging: capture a window instead.
     Window,
 }
@@ -46,12 +49,12 @@ pub enum Choice {
 pub struct Overlay {
     surfaces: Vec<Surface>,
     selection: Selection,
-    /// Output where the current drag started; the capture is clipped to it.
-    anchor: Option<usize>,
     /// Shift, Alt and Space as the keyboard last reported them.
     mods: Mods,
-    /// The surface the pointer is on and its surface-local position.
+    /// The pointer in global logical coordinates. A drag's events keep
-    pointer: Option<(usize, (f64, f64))>,
+    /// arriving on the surface it started on, with positions past its
+    /// edges, so this stays right across outputs.
+    pointer: Option<Point>,
     outcome: Option<Option<Choice>>,
 }
 
@@ -68,6 +71,9 @@ struct Surface {
     configured: bool,
     frame_pending: bool,
     dirty: bool,
+    /// The selection part and whether the label were last drawn here.
+    shown: Option<PixelRect>,
+    labelled: bool,
 }
 
 /// Shows the overlay on every output and waits for a selection.
@@ -114,7 +120,6 @@ pub fn select(wl: &mut Wayland, outputs: &[Output], frames: &[Frame]) -> Result<
     wl.state.overlay = Some(Overlay {
         surfaces,
         selection: Selection::default(),
-        anchor: None,
         mods: Mods::default(),
         pointer: None,
         outcome: None,
@@ -127,6 +132,21 @@ pub fn select(wl: &mut Wayland, outputs: &[Output], frames: &[Frame]) -> Result<
     outcome.flatten().ok_or_else(|| Cancelled.into())
 }
 
+/// What a finished drag from `a` to `b` captures: one output's crop as
+/// before, or the whole rectangle to stitch; `None` for a click.
+fn choose(
+    a: Point,
+    b: Point,
+    outputs: &[(&OutputGeom, (u32, u32))],
+    pointer: Point,
+) -> Option<Choice> {
+    let span = selection::span(a, b, outputs)?;
+    Some(match span.single() {
+        Some((i, rect)) => Choice::Region(i, rect),
+        None => Choice::Span(span, selection::locate(pointer, outputs)),
+    })
+}
+
 impl Surface {
     fn new(
         layer: LayerSurface,
@@ -151,6 +171,8 @@ impl Surface {
             configured: false,
             frame_pending: false,
             dirty: true,
+            shown: None,
+            labelled: false,
         })
     }
 
@@ -227,9 +249,7 @@ impl Overlay {
 
     fn apply_mods(&mut self, qh: &QueueHandle<State>) {
         self.selection.set_mods(self.mods);
-        if let Some(a) = self.anchor {
+        self.redraw_changed(qh);
-            self.redraw(a, qh);
-        }
     }
 
     pub fn switch_to_window(&mut self) {
@@ -245,26 +265,64 @@ impl Overlay {
             .position(|s| s.layer.wl_surface() == surface)
     }
 
-    /// The selection as drawn on surface `i`: only the anchor output shows it.
+    fn outputs(&self) -> Vec<(&OutputGeom, (u32, u32))> {
+        self.surfaces
+            .iter()
+            .map(|s| (&s.geom, (s.width, s.height)))
+            .collect()
+    }
+
+    /// The selection's part on surface `i`.
     fn selection_on(&self, i: usize) -> Option<PixelRect> {
         let (start, end) = self.selection.corners()?;
         let s = &self.surfaces[i];
-        (self.anchor == Some(i))
+        selection::clip(start, end, &s.geom, s.width, s.height)
-            .then(|| selection::clip(start, end, &s.geom, s.width, s.height))
+    }
-            .flatten()
+
+    /// The size label on surface `i`: the whole shot's size next to the
+    /// pointer, on the output the pointer is over.
+    fn label_on(&self, i: usize) -> Option<(PixelRect, (f64, f64))> {
+        let (start, end) = self.selection.corners()?;
+        let p = self.pointer?;
+        let outputs = self.outputs();
+        if selection::locate(p, &outputs) != i {
+            return None;
+        }
+        let (width, height) = selection::span(start, end, &outputs)?.size;
+        let g = &self.surfaces[i].geom;
+        Some((
+            PixelRect {
+                x: 0,
+                y: 0,
+                width,
+                height,
+            },
+            (p.x - g.x as f64, p.y - g.y as f64),
+        ))
     }
 
     fn redraw(&mut self, i: usize, qh: &QueueHandle<State>) {
         let sel = self.selection_on(i);
-        // The size label goes next to the pointer, on the output it is on.
+        let label = self.label_on(i);
-        let label = sel.zip(self.pointer.filter(|(on, _)| *on == i).map(|(_, at)| at));
         let s = &mut self.surfaces[i];
+        s.shown = sel;
+        s.labelled = label.is_some();
         s.dirty = true;
         if s.configured && !s.frame_pending {
             s.draw(sel, label, qh);
         }
     }
 
+    /// Redraws the surfaces whose part of the selection or label changed.
+    fn redraw_changed(&mut self, qh: &QueueHandle<State>) {
+        for i in 0..self.surfaces.len() {
+            let s = &self.surfaces[i];
+            if self.selection_on(i) != s.shown || s.labelled || self.label_on(i).is_some() {
+                self.redraw(i, qh);
+            }
+        }
+    }
+
     pub fn configure(&mut self, layer: &LayerSurface, (w, h): (u32, u32), qh: &QueueHandle<State>) {
         let Some(i) = self.index_of(layer.wl_surface()) else {
             return;
@@ -303,12 +361,12 @@ impl Overlay {
             let Some(i) = self.index_of(&event.surface) else {
                 continue;
             };
-            self.pointer = Some((i, event.position));
             let g = &self.surfaces[i].geom;
             let p = Point {
                 x: g.x as f64 + event.position.0,
                 y: g.y as f64 + event.position.1,
             };
+            self.pointer = Some(p);
             match event.kind {
                 PointerEventKind::Enter { serial } => {
                     if let Some(cursor) = cursor {
@@ -320,35 +378,29 @@ impl Overlay {
                 } => {
                     // Modifiers already held apply from the start.
                     self.selection.press_with(p, self.mods);
-                    self.anchor = Some(i);
+                    self.redraw_changed(qh);
                 }
                 PointerEventKind::Press {
                     button: BTN_RIGHT, ..
                 } => self.cancel(),
                 PointerEventKind::Motion { .. } => {
                     self.selection.motion(p);
-                    if let Some(a) = self.anchor {
+                    self.redraw_changed(qh);
-                        self.redraw(a, qh);
-                    }
                 }
                 PointerEventKind::Release {
                     button: BTN_LEFT, ..
                 } => {
-                    let (Some((start, end)), Some(a)) = (self.selection.release(p), self.anchor)
+                    let Some((start, end)) = self.selection.release(p) else {
-                    else {
                         continue;
                     };
-                    let s = &self.surfaces[a];
+                    let choice = choose(start, end, &self.outputs(), p);
-                    match selection::resolve(start, end, &s.geom, s.width, s.height) {
+                    match choice {
-                        Some(rect) => {
+                        Some(choice) => {
-                            tracing::info!(
+                            tracing::info!("selected {choice:?} (logical {start:?} to {end:?})");
-                                "selected {rect:?} on {} (logical {start:?} to {end:?})",
+                            self.outcome = Some(Some(choice));
-                                s.geom.name
-                            );
-                            self.outcome = Some(Some(Choice::Region(a, rect)));
                         }
                         // A click, not a drag: clear it and keep waiting.
-                        None => self.redraw(a, qh),
+                        None => self.redraw_changed(qh),
                     }
                 }
                 _ => {}
@@ -356,3 +408,65 @@ impl Overlay {
         }
     }
 }
+
+#[cfg(test)]
+mod tests {
+    use super::*;
+
+    fn out(name: &str, x: i32, y: i32, width: i32, height: i32) -> OutputGeom {
+        OutputGeom {
+            name: name.into(),
+            x,
+            y,
+            width,
+            height,
+        }
+    }
+
+    fn p(x: f64, y: f64) -> Point {
+        Point { x, y }
+    }
+
+    #[test]
+    fn one_output_is_todays_region_and_several_a_span() {
+        let laptop = out("LVDS-1", 0, 0, 1366, 768);
+        let monitor = out("HDMI-A-1", -277, -1080, 1920, 1080);
+        let outputs = [(&laptop, (1366, 768)), (&monitor, (1920, 1080))];
+        assert_eq!(
+            choose(p(100.0, 100.0), p(300.0, 250.0), &outputs, p(300.0, 250.0)),
+            Some(Choice::Region(
+                0,
+                PixelRect {
+                    x: 100,
+                    y: 100,
+                    width: 200,
+                    height: 150
+                }
+            ))
+        );
+        let across = choose(
+            p(100.0, 500.0),
+            p(600.0, -300.0),
+            &outputs,
+            p(600.0, -300.0),
+        );
+        let Some(Choice::Span(span, on)) = across else {
+            panic!("expected a span, got {across:?}");
+        };
+        assert_eq!(
+            (span.size, span.parts.len(), on),
+            ((500, 800), 2, 1),
+            "preview on the monitor"
+        );
+        // A box touching only the laptop but reaching past its left edge.
+        assert!(matches!(
+            choose(p(-50.0, 100.0), p(200.0, 300.0), &outputs, p(200.0, 300.0)),
+            Some(Choice::Span(_, 0))
+        ));
+        assert_eq!(
+            choose(p(10.0, 10.0), p(11.0, 30.0), &outputs, p(11.0, 30.0)),
+            None,
+            "a click"
+        );
+    }
+}

src/selection.rs

@@ -183,17 +183,6 @@ pub fn clip(a: Point, b: Point, out: &OutputGeom, frame_w: u32, frame_h: u32) ->
     })
 }
 
-/// Like [`clip`], but treats anything under [`MIN_PIXELS`] as a click.
-pub fn resolve(
-    a: Point,
-    b: Point,
-    out: &OutputGeom,
-    frame_w: u32,
-    frame_h: u32,
-) -> Option<PixelRect> {
-    clip(a, b, out, frame_w, frame_h).filter(|r| r.width >= MIN_PIXELS && r.height >= MIN_PIXELS)
-}
-
 /// One output's share of a selection and where it goes in the whole image.
 #[derive(Debug, Clone, PartialEq)]
 pub struct Part {
@@ -412,11 +401,12 @@ mod tests {
     #[test]
     fn click_is_not_a_selection() {
         let o = out("A", 0, 0, 1920, 1080);
-        assert_eq!(resolve(p(10.0, 10.0), p(10.0, 10.0), &o, 1920, 1080), None);
+        let outputs = [(&o, (1920, 1080))];
-        assert_eq!(resolve(p(10.0, 10.0), p(11.0, 30.0), &o, 1920, 1080), None);
+        assert_eq!(span(p(10.0, 10.0), p(10.0, 10.0), &outputs), None);
+        assert_eq!(span(p(10.0, 10.0), p(11.0, 30.0), &outputs), None);
         assert_eq!(
-            resolve(p(10.0, 10.0), p(12.0, 12.0), &o, 1920, 1080),
+            span(p(10.0, 10.0), p(12.0, 12.0), &outputs).and_then(|s| s.single()),
-            Some(rect(10, 10, 2, 2))
+            Some((0, rect(10, 10, 2, 2)))
         );
     }