From 3495b42afa93f76a3028465faa16319716d53e35 Mon Sep 17 00:00:00 2001
From: elwrcl <elwerici@proton.me>
Date: Sun, 4 Oct 2026 20:44:47 +0300
Subject: [PATCH] stitch: a selection over several outputs as one image

---
 src/main.rs   |   1 +
 src/stitch.rs | 116 ++++++++++++++++++++++++++++++++++++++++++++++++++
 2 files changed, 117 insertions(+)
 create mode 100644 src/stitch.rs

diff --git a/src/main.rs b/src/main.rs
index bdce52f..90fe397 100644
--- a/src/main.rs
+++ b/src/main.rs
@@ -20,6 +20,7 @@ mod selection;
 mod shadow;
 mod sound;
 mod stack;
+mod stitch;
 mod theme;
 mod thumbnail;
 mod toolbar;
diff --git a/src/stitch.rs b/src/stitch.rs
new file mode 100644
index 0000000..40b49da
--- /dev/null
+++ b/src/stitch.rs
@@ -0,0 +1,116 @@
+//! A selection over several outputs as one image.
+
+use image::{RgbaImage, imageops};
+
+use crate::frame::Frame;
+use crate::selection::Span;
+
+/// The whole selection: each output's part from its frozen frame at its
+/// place (resized when its output's scale is smaller), transparent where
+/// no output is.
+pub fn stitch(frames: &[Frame], span: &Span) -> RgbaImage {
+    let mut image = RgbaImage::new(span.size.0, span.size.1);
+    for part in &span.parts {
+        let mut crop = frames[part.output].to_rgba(part.rect);
+        if crop.dimensions() != part.size {
+            crop = imageops::resize(
+                &crop,
+                part.size.0,
+                part.size.1,
+                imageops::FilterType::Triangle,
+            );
+        }
+        imageops::replace(&mut image, &crop, part.at.0 as i64, part.at.1 as i64);
+    }
+    image
+}
+
+#[cfg(test)]
+mod tests {
+    use std::sync::Arc;
+
+    use image::RgbaImage;
+
+    use super::*;
+    use crate::frame::{Frame, OutputGeom, PixelRect};
+    use crate::selection::{Part, Span};
+
+    /// A frame of one colour, given as R, G, B (stored as B, G, R, X).
+    fn frame(w: u32, h: u32, rgb: [u8; 3]) -> Frame {
+        Frame {
+            output: OutputGeom {
+                name: "X".into(),
+                x: 0,
+                y: 0,
+                width: w as i32,
+                height: h as i32,
+            },
+            pixels: Arc::new(RgbaImage::from_pixel(
+                w,
+                h,
+                image::Rgba([rgb[2], rgb[1], rgb[0], 0]),
+            )),
+        }
+    }
+
+    fn rect(x: u32, y: u32, width: u32, height: u32) -> PixelRect {
+        PixelRect {
+            x,
+            y,
+            width,
+            height,
+        }
+    }
+
+    #[test]
+    fn parts_land_in_place_and_gaps_stay_clear() {
+        let frames = [frame(10, 10, [255, 0, 0]), frame(10, 10, [0, 0, 255])];
+        let span = Span {
+            size: (8, 6),
+            parts: vec![
+                Part {
+                    output: 0,
+                    rect: rect(0, 0, 4, 3),
+                    at: (4, 3),
+                    size: (4, 3),
+                },
+                Part {
+                    output: 1,
+                    rect: rect(2, 2, 8, 3),
+                    at: (0, 0),
+                    size: (8, 3),
+                },
+            ],
+        };
+        let img = stitch(&frames, &span);
+        assert_eq!(img.dimensions(), (8, 6));
+        assert_eq!(
+            img.get_pixel(0, 0).0,
+            [0, 0, 255, 255],
+            "the monitor's part, opaque"
+        );
+        assert_eq!(img.get_pixel(7, 2).0, [0, 0, 255, 255]);
+        assert_eq!(img.get_pixel(5, 4).0, [255, 0, 0, 255], "the laptop's part");
+        assert_eq!(img.get_pixel(1, 4).0[3], 0, "no output there: transparent");
+    }
+
+    #[test]
+    fn a_smaller_scale_part_is_resized_to_its_place() {
+        let frames = [frame(4, 4, [0, 255, 0])];
+        let span = Span {
+            size: (8, 8),
+            parts: vec![Part {
+                output: 0,
+                rect: rect(0, 0, 4, 4),
+                at: (0, 0),
+                size: (8, 8),
+            }],
+        };
+        let img = stitch(&frames, &span);
+        assert_eq!(
+            img.get_pixel(7, 7).0,
+            [0, 255, 0, 255],
+            "filled to the corner"
+        );
+    }
+}