fix: show finished shapes as the export draws them

src/editor/doc.rs

@@ -8,6 +8,7 @@ pub struct Doc {
     shapes: Vec<Shape>,
     redo: Vec<Shape>,
     saved: Vec<Shape>,
+    revision: u64,
 }
 
 impl Doc {
@@ -22,6 +23,7 @@ impl Doc {
     pub fn add(&mut self, shape: Shape) {
         self.shapes.push(shape);
         self.redo.clear();
+        self.revision += 1;
     }
 
     pub fn undo(&mut self) -> bool {
@@ -29,6 +31,7 @@ impl Doc {
             return false;
         };
         self.redo.push(shape);
+        self.revision += 1;
         true
     }
 
@@ -37,9 +40,15 @@ impl Doc {
             return false;
         };
         self.shapes.push(shape);
+        self.revision += 1;
         true
     }
 
+    /// Changes whenever the drawn shapes do.
+    pub fn revision(&self) -> u64 {
+        self.revision
+    }
+
     pub fn can_undo(&self) -> bool {
         !self.shapes.is_empty()
     }
@@ -87,6 +96,24 @@ mod tests {
         assert!(!d.redo());
     }
 
+    #[test]
+    fn revision_follows_the_shapes() {
+        let mut d = Doc::new();
+        let r0 = d.revision();
+        d.add(line(1.0));
+        let r1 = d.revision();
+        assert_ne!(r1, r0);
+        d.mark_saved();
+        assert_eq!(d.revision(), r1, "saving doesn't change what is drawn");
+        d.undo();
+        assert_ne!(d.revision(), r1);
+        let r2 = d.revision();
+        assert!(!d.undo(), "nothing left");
+        assert_eq!(d.revision(), r2);
+        d.redo();
+        assert_ne!(d.revision(), r2);
+    }
+
     #[test]
     fn a_new_shape_clears_redo() {
         let mut d = Doc::new();

src/editor/mod.rs

@@ -52,7 +52,11 @@ pub fn run(path: &Path) -> Result<()> {
 struct Editor {
     path: PathBuf,
     base: RgbaImage,
+    /// The base with every finished shape, drawn by the export renderer so
+    /// the canvas shows the saved pixels.
     texture: egui::TextureHandle,
+    /// The `Doc::revision` the texture shows.
+    shown: u64,
     doc: Doc,
     tool: Tool,
     color: usize,
@@ -74,6 +78,7 @@ impl Editor {
             path,
             base,
             texture,
+            shown: 0,
             doc: Doc::new(),
             tool: Tool::Arrow,
             color: 0,
@@ -299,6 +304,14 @@ impl Editor {
             Color32::WHITE,
         );
 
+        if self.doc.revision() != self.shown {
+            let composite = export::render(&self.base, self.doc.shapes());
+            let size = [composite.width() as usize, composite.height() as usize];
+            let pixels = egui::ColorImage::from_rgba_unmultiplied(size, composite.as_raw());
+            self.texture.set(pixels, egui::TextureOptions::LINEAR);
+            self.shown = self.doc.revision();
+        }
+
         let shift = ui.input(|i| i.modifiers.shift);
         let pointer = response
             .interact_pointer_pos()
@@ -321,9 +334,10 @@ impl Editor {
             }
         }
 
-        let live = self.drag.as_ref().map(|d| d.shape(shift));
-        for shape in self.doc.shapes().iter().chain(live.as_ref()) {
-            for prim in geometry(shape) {
+        // Finished shapes are in the texture; only the one being drawn is
+        // painted here.
+        if let Some(live) = self.drag.as_ref().map(|d| d.shape(shift)) {
+            for prim in geometry(&live) {
                 paint(&painter, &prim, fit.scale, to_pos);
             }
         }