handwritin: Grow and shrink the canvas without refreshing

src/handwriting/canvas_rasterizer.rs

@@ -18,6 +18,7 @@ const CHUNK_SIZE: usize = 64;
 /// Rasterize onto a resizeable canvas.
 #[derive(Default)]
 pub struct CanvasRasterizer {
+    image_size: [usize; 2],
     tiles: HashMap<[usize; 2], Tile>,
 }
 
@@ -49,12 +50,30 @@ impl Tile {
 }
 
 impl CanvasRasterizer {
-    //pub fn clear(&mut self) {
-    //    self.image = ColorImage::new(self.image.size, Color32::TRANSPARENT);
-    //    self.texture_is_dirty = true;
-    //}
-
     pub fn set_size(&mut self, width: usize, height: usize) {
+        self.image_size = [width, height];
+        self.populate_tiles();
+    }
+
+    pub fn clear(&mut self) {
+        log::error!("clearing all tiles");
+        self.tiles.clear();
+        self.populate_tiles();
+    }
+
+    pub fn clear_and_set_size(&mut self, width: usize, height: usize) {
+        self.image_size = [width, height];
+        self.clear();
+    }
+
+    fn populate_tiles(&mut self) {
+        let [width, height] = self.image_size;
+
+        // discard tiles that are out of bounds
+        self.tiles.retain(|_, tile| {
+            tile.bounding_box.x_from <= width && tile.bounding_box.y_from <= height
+        });
+
         let chunk = |max: usize| {
             (0..)
                 .step_by(CHUNK_SIZE)
@@ -62,6 +81,7 @@ impl CanvasRasterizer {
                 .enumerate()
         };
 
+        // create new tiles where we need them
         for (xi, _x) in chunk(width) {
             for (yi, _y) in chunk(height) {
                 self.tiles
@@ -71,13 +91,6 @@ impl CanvasRasterizer {
         }
     }
 
-    pub fn clear_and_set_size(&mut self, width: usize, height: usize) {
-        log::error!("clearing all tiles");
-        self.tiles.clear();
-
-        self.set_size(width, height);
-    }
-
     pub fn rasterize<'a>(
         &mut self,
         point_to_pixel: TSTransform,

src/handwriting/mod.rs

@@ -105,20 +105,9 @@ struct MeshContext {
 
     pub pixels_per_point: f32,
 
-    /// Canvas size in points
-    pub size: Vec2,
-
     pub stroke: Stroke,
 }
 
-impl MeshContext {
-    /// Calculate canvas size in pixels
-    pub fn pixel_size(&self) -> [usize; 2] {
-        let Vec2 { x, y } = self.size * self.pixels_per_point;
-        [x, y].map(|f| f.ceil() as usize)
-    }
-}
-
 impl Default for Handwriting {
     fn default() -> Self {
         Self {
@@ -379,7 +368,6 @@ impl Handwriting {
         let new_context = MeshContext {
             ui_theme: ui.ctx().theme(),
             pixels_per_point: ui.pixels_per_point(),
-            size: mesh_rect.size(),
             stroke: style.stroke,
         };
 
@@ -388,6 +376,13 @@ impl Handwriting {
             self.e.refresh_texture = true;
         }
 
+        let [px_width, px_height] = {
+            let Vec2 { x, y } = mesh_rect.size() * new_context.pixels_per_point;
+            [x, y].map(|f| f.ceil() as usize)
+        };
+
+        self.e.canvas_rasterizer.set_size(px_width, px_height);
+
         if self.e.refresh_texture {
             // ...if we do, rasterize the entire texture from scratch
             self.refresh_texture(style, new_context);
@@ -457,11 +452,10 @@ impl Handwriting {
         //    debug_assert!(vertex.pos.y.is_finite(), "{} must be finite", vertex.pos.y);
         //}
 
-        let [px_x, px_y] = mesh_context.pixel_size();
         let point_to_pixel = TSTransform::from_scaling(mesh_context.pixels_per_point);
         let triangles = mesh_triangles(&self.e.mesh);
 
-        self.e.canvas_rasterizer.clear_and_set_size(px_x, px_y);
+        self.e.canvas_rasterizer.clear();
         self.e
             .canvas_rasterizer
             .rasterize(point_to_pixel, triangles);