Split CanvasRasterizer image into many small tiles

src/rasterizer.rs

@@ -1,5 +1,6 @@
 use core::f32;
 use egui::{Color32, ColorImage, Pos2, Rect, Vec2, emath::TSTransform, epaint::Vertex};
+use std::ops::Range;
 
 pub trait BlendFn {
     fn blend(a: Color32, b: Color32) -> Color32;
@@ -88,7 +89,7 @@ pub fn rasterize_onto<'a, Blend: BlendFn>(
 
 /// A bounding box, measured in pixels.
 #[derive(Debug, PartialEq, Eq)]
-struct PxBoundingBox {
+pub struct PxBoundingBox {
     pub x_from: usize,
     pub y_from: usize,
     pub x_to: usize,
@@ -104,9 +105,42 @@ impl PxBoundingBox {
             y_to: self.y_to.min(other.y_to),
         }
     }
+
+    pub fn union(&self, other: &PxBoundingBox) -> PxBoundingBox {
+        PxBoundingBox {
+            x_from: self.x_from.min(other.x_from),
+            y_from: self.y_from.min(other.y_from),
+            x_to: self.x_to.max(other.x_to),
+            y_to: self.y_to.max(other.y_to),
+        }
+    }
+
+    pub fn x_range(&self) -> Range<usize> {
+        self.x_from..self.x_to
+    }
+
+    pub fn y_range(&self) -> Range<usize> {
+        self.y_from..self.y_to
+    }
+
+    /// Test whether two boxes do NOT overlap
+    pub fn overlaps_with(&self, other: &PxBoundingBox) -> bool {
+        !self.is_disjoint_from(other)
+    }
+
+    pub fn is_disjoint_from(&self, other: &PxBoundingBox) -> bool {
+        false
+            || self.x_from > other.x_to
+            || self.y_from > other.y_to
+            || other.x_from > self.x_to
+            || other.y_from > self.y_to
+    }
 }
 
-fn triangle_bounding_box(triangle: &[&Vertex; 3], point_to_pixel: TSTransform) -> PxBoundingBox {
+pub fn triangle_bounding_box(
+    triangle: &[&Vertex; 3],
+    point_to_pixel: TSTransform,
+) -> PxBoundingBox {
     // calculate bounding box in point coords
     let mut rect = Rect::NOTHING;
     for vertex in triangle {