diff --git a/Cargo.lock b/Cargo.lock
index ff30ad2..d7fac33 100644
--- a/Cargo.lock
+++ b/Cargo.lock
@@ -82,6 +82,18 @@ version = "1.0.104"
 source = "registry+https://github.com/rust-lang/crates.io-index"
 checksum = "330a5ed07fa54e4702c9d6c4174f74427fc0ef6e214bbd677ae50a5099946470"
 
+[[package]]
+name = "arrayref"
+version = "0.3.9"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "76a2e8124351fda1ef8aaaa3bbd7ebbcb486bbcd4225aca0aa0d84bb2db8fecb"
+
+[[package]]
+name = "arrayvec"
+version = "0.7.8"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "d3fb67a6e08acf24fdeccbac2cb6ac4305825bd1f117462e0e6f2f193345ad56"
+
 [[package]]
 name = "autocfg"
 version = "1.5.1"
@@ -901,6 +913,12 @@ dependencies = [
  "xkeysym",
 ]
 
+[[package]]
+name = "strict-num"
+version = "0.1.1"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "6637bab7722d379c8b41ba849228d680cc12d0a45ba1fa2b48f2a30577a06731"
+
 [[package]]
 name = "strsim"
 version = "0.11.1"
@@ -971,6 +989,32 @@ dependencies = [
  "cfg-if",
 ]
 
+[[package]]
+name = "tiny-skia"
+version = "0.12.0"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "47ffee5eaaf5527f630fb0e356b90ebdec84d5d18d937c5e440350f88c5a91ea"
+dependencies = [
+ "arrayref",
+ "arrayvec",
+ "bytemuck",
+ "cfg-if",
+ "log",
+ "png",
+ "tiny-skia-path",
+]
+
+[[package]]
+name = "tiny-skia-path"
+version = "0.12.0"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "edca365c3faccca67d06593c5980fa6c57687de727a03131735bb85f01fdeeb9"
+dependencies = [
+ "arrayref",
+ "bytemuck",
+ "strict-num",
+]
+
 [[package]]
 name = "toml"
 version = "1.1.6+spec-1.1.0"
@@ -1120,6 +1164,7 @@ dependencies = [
  "serde_json",
  "smithay-client-toolkit",
  "tempfile",
+ "tiny-skia",
  "toml",
  "tracing",
  "tracing-subscriber",
diff --git a/Cargo.toml b/Cargo.toml
index 13c69fc..cf69cc6 100644
--- a/Cargo.toml
+++ b/Cargo.toml
@@ -20,6 +20,7 @@ serde = { version = "1.0.229", features = ["derive"] }
 serde_ignored = "0.1.14"
 serde_json = "1.0.151"
 smithay-client-toolkit = "0.21.1"
+tiny-skia = "0.12.0"
 toml = "1.1.6"
 tracing = "0.1.44"
 tracing-subscriber = { version = "0.3.23", features = ["env-filter"] }
diff --git a/src/editor/export.rs b/src/editor/export.rs
new file mode 100644
index 0000000..c1657ce
--- /dev/null
+++ b/src/editor/export.rs
@@ -0,0 +1,158 @@
+//! The edited image at full resolution: the base plus every shape,
+//! drawn with tiny-skia from the same geometry as the canvas.
+
+use std::path::{Path, PathBuf};
+
+use image::RgbaImage;
+use tiny_skia::{FillRule, LineCap, LineJoin, Paint, PathBuilder, Pixmap, Stroke, Transform};
+
+use crate::editor::shape::{Prim, Shape, geometry};
+
+pub fn render(base: &RgbaImage, shapes: &[Shape]) -> RgbaImage {
+    let (w, h) = base.dimensions();
+    let mut pixmap = Pixmap::new(w, h).expect("the image has a size");
+    for (dst, src) in pixmap.pixels_mut().iter_mut().zip(base.pixels()) {
+        let [r, g, b, a] = src.0;
+        *dst = tiny_skia::ColorU8::from_rgba(r, g, b, a).premultiply();
+    }
+    for prim in shapes.iter().flat_map(geometry) {
+        draw(&mut pixmap, &prim);
+    }
+    let mut out = RgbaImage::new(w, h);
+    for (dst, src) in out.pixels_mut().zip(pixmap.pixels()) {
+        let c = src.demultiply();
+        dst.0 = [c.red(), c.green(), c.blue(), c.alpha()];
+    }
+    out
+}
+
+fn draw(pixmap: &mut Pixmap, prim: &Prim) {
+    let (points, color) = match prim {
+        Prim::Stroke { points, color, .. } | Prim::Fill { points, color } => (points, color),
+    };
+    let mut pb = PathBuilder::new();
+    pb.move_to(points[0].0, points[0].1);
+    for p in &points[1..] {
+        pb.line_to(p.0, p.1);
+    }
+    let closed = matches!(prim, Prim::Fill { .. } | Prim::Stroke { closed: true, .. });
+    if closed {
+        pb.close();
+    }
+    let Some(path) = pb.finish() else { return };
+    let mut paint = Paint::default();
+    paint.set_color_rgba8(color[0], color[1], color[2], color[3]);
+    paint.anti_alias = true;
+    match prim {
+        Prim::Fill { .. } => pixmap.fill_path(
+            &path,
+            &paint,
+            FillRule::Winding,
+            Transform::identity(),
+            None,
+        ),
+        Prim::Stroke { width, round, .. } => {
+            let stroke = Stroke {
+                width: *width,
+                line_cap: if *round {
+                    LineCap::Round
+                } else {
+                    LineCap::Butt
+                },
+                line_join: if *round {
+                    LineJoin::Round
+                } else {
+                    LineJoin::Miter
+                },
+                ..Stroke::default()
+            };
+            pixmap.stroke_path(&path, &paint, &stroke, Transform::identity(), None);
+        }
+    }
+}
+
+/// `<stem> edited.png` next to `path`, numbered if taken.
+pub fn edited_path(path: &Path) -> PathBuf {
+    let dir = path.parent().unwrap_or(Path::new("."));
+    let stem = path
+        .file_stem()
+        .map(|s| s.to_string_lossy())
+        .unwrap_or_default();
+    crate::output::unique_path(dir, &format!("{stem} edited.png"))
+}
+
+#[cfg(test)]
+mod tests {
+    use super::*;
+    use crate::editor::shape::{Style, Tool};
+    use image::Rgba;
+
+    fn line(tool: Tool, color: [u8; 3]) -> Shape {
+        Shape {
+            tool,
+            style: Style { color, width: 4.0 },
+            points: vec![(10.0, 20.0), (90.0, 20.0)],
+        }
+    }
+
+    #[test]
+    fn line_pixels() {
+        let base = RgbaImage::from_pixel(100, 40, Rgba([255, 255, 255, 255]));
+        let out = render(&base, &[line(Tool::Line, [255, 0, 0])]);
+        assert_eq!(out.dimensions(), (100, 40));
+        assert_eq!(out.get_pixel(50, 20).0, [255, 0, 0, 255], "on the line");
+        assert_eq!(out.get_pixel(50, 5).0, [255, 255, 255, 255], "away from it");
+        assert_eq!(
+            out.get_pixel(5, 20).0,
+            [255, 255, 255, 255],
+            "before its start cap"
+        );
+    }
+
+    #[test]
+    fn highlighter_blends_at_40_percent() {
+        let base = RgbaImage::from_pixel(100, 40, Rgba([0, 0, 255, 255]));
+        let out = render(&base, &[line(Tool::Highlighter, [255, 255, 0])]);
+        let [r, g, b, a] = out.get_pixel(50, 20).0;
+        assert_eq!(a, 255);
+        for (got, want) in [(r, 102), (g, 102), (b, 153)] {
+            assert!(
+                (got as i32 - want).abs() <= 2,
+                "{:?}",
+                out.get_pixel(50, 20)
+            );
+        }
+    }
+
+    #[test]
+    fn keeps_transparency() {
+        let base = RgbaImage::from_pixel(100, 40, Rgba([10, 20, 30, 0]));
+        let mut half = base.clone();
+        half.put_pixel(50, 5, Rgba([200, 100, 50, 128]));
+        let out = render(&half, &[line(Tool::Line, [255, 0, 0])]);
+        assert_eq!(out.get_pixel(0, 0).0[3], 0, "transparent stays transparent");
+        let [r, g, b, a] = out.get_pixel(50, 5).0;
+        assert_eq!(a, 128);
+        assert!(
+            (r as i32 - 200).abs() <= 2
+                && (g as i32 - 100).abs() <= 2
+                && (b as i32 - 50).abs() <= 2
+        );
+        assert_eq!(out.get_pixel(50, 20).0, [255, 0, 0, 255]);
+    }
+
+    #[test]
+    fn edited_path_sits_next_to_the_file() {
+        let dir = tempfile::tempdir().unwrap();
+        let file = dir.path().join("Screenshot at 10.00.png");
+        assert_eq!(
+            edited_path(&file),
+            dir.path().join("Screenshot at 10.00 edited.png")
+        );
+        std::fs::write(dir.path().join("Screenshot at 10.00 edited.png"), b"x").unwrap();
+        assert_ne!(
+            edited_path(&file),
+            dir.path().join("Screenshot at 10.00 edited.png")
+        );
+    }
+}
diff --git a/src/editor/mod.rs b/src/editor/mod.rs
index 761a10c..45cb688 100644
--- a/src/editor/mod.rs
+++ b/src/editor/mod.rs
@@ -1,4 +1,6 @@
 //! `valw edit`: a Markup-like editor window (eframe, OpenGL ES).
 
 pub mod doc;
+pub mod export;
 pub mod shape;
+pub mod view;
diff --git a/src/editor/view.rs b/src/editor/view.rs
new file mode 100644
index 0000000..23215b1
--- /dev/null
+++ b/src/editor/view.rs
@@ -0,0 +1,93 @@
+//! Fitting the image into the canvas: image pixels ↔ egui points.
+
+use crate::editor::shape::P;
+
+#[derive(Debug, Clone, Copy, PartialEq)]
+pub struct Fit {
+    /// Points per image pixel.
+    pub scale: f32,
+    /// Where the image's top-left corner is, in points.
+    pub offset: P,
+}
+
+impl Fit {
+    /// Fits `image` into `area` (x, y, w, h in points), centred, never
+    /// above 100 % (one image pixel per physical pixel).
+    pub fn new(image: (u32, u32), area: (f32, f32, f32, f32), pixels_per_point: f32) -> Fit {
+        let (iw, ih) = (image.0 as f32, image.1 as f32);
+        let (x, y, w, h) = area;
+        let scale = (w / iw).min(h / ih).min(1.0 / pixels_per_point);
+        Fit {
+            scale,
+            offset: (x + (w - iw * scale) / 2.0, y + (h - ih * scale) / 2.0),
+        }
+    }
+
+    pub fn to_screen(self, p: P) -> P {
+        (
+            self.offset.0 + p.0 * self.scale,
+            self.offset.1 + p.1 * self.scale,
+        )
+    }
+
+    pub fn to_image(self, p: P) -> P {
+        (
+            (p.0 - self.offset.0) / self.scale,
+            (p.1 - self.offset.1) / self.scale,
+        )
+    }
+}
+
+/// `p` moved onto the image's area.
+pub fn clamp(p: P, image: (u32, u32)) -> P {
+    (
+        p.0.clamp(0.0, image.0 as f32),
+        p.1.clamp(0.0, image.1 as f32),
+    )
+}
+
+#[cfg(test)]
+mod tests {
+    use super::*;
+
+    #[test]
+    fn small_images_are_not_upscaled() {
+        let f = Fit::new((400, 300), (0.0, 50.0, 1000.0, 800.0), 1.0);
+        assert_eq!(f.scale, 1.0);
+        assert_eq!(f.offset, (300.0, 300.0), "centred");
+    }
+
+    #[test]
+    fn large_images_fit_the_area() {
+        let f = Fit::new((1920, 1080), (0.0, 40.0, 960.0, 1000.0), 1.0);
+        assert_eq!(f.scale, 0.5);
+        assert_eq!(f.offset, (0.0, 40.0 + (1000.0 - 540.0) / 2.0));
+    }
+
+    #[test]
+    fn hundred_percent_means_one_image_pixel_per_physical_pixel() {
+        let f = Fit::new((400, 300), (0.0, 0.0, 1000.0, 800.0), 2.0);
+        assert_eq!(
+            f.scale, 0.5,
+            "0.5 points per image px at 2× = 1 physical px"
+        );
+    }
+
+    #[test]
+    fn round_trip() {
+        let f = Fit::new((1920, 1080), (10.0, 40.0, 1000.0, 700.0), 1.25);
+        for p in [(0.0, 0.0), (1919.0, 1079.0), (333.5, 777.25)] {
+            let q = f.to_image(f.to_screen(p));
+            assert!(
+                (q.0 - p.0).abs() < 1e-3 && (q.1 - p.1).abs() < 1e-3,
+                "{p:?} {q:?}"
+            );
+        }
+    }
+
+    #[test]
+    fn clamp_keeps_points_on_the_image() {
+        assert_eq!(clamp((-5.0, 50.0), (100, 80)), (0.0, 50.0));
+        assert_eq!(clamp((150.0, 90.0), (100, 80)), (100.0, 80.0));
+    }
+}