Speed up fractal_clock painting (#152)

clip unwatchable line before drawing

egui/src/painter.rs

@@ -116,6 +116,9 @@ impl Painter {
             .add(self.clip_rect, shape)
     }
 
+    /// Add many shapes at once.
+    ///
+    /// Calling this once is generally faster than calling [`Self::add`] multiple times.
     pub fn extend(&self, shapes: Vec<Shape>) {
         if !shapes.is_empty() {
             self.ctx

egui_demo_lib/src/apps/fractal_clock.rs

@@ -13,6 +13,7 @@ pub struct FractalClock {
     length_factor: f32,
     luminance_factor: f32,
     width_factor: f32,
+    line_count: usize,
 }
 
 impl Default for FractalClock {
@@ -26,6 +27,7 @@ impl Default for FractalClock {
             length_factor: 0.8,
             luminance_factor: 0.8,
             width_factor: 0.9,
+            line_count: 0,
         }
     }
 }
@@ -79,6 +81,7 @@ impl FractalClock {
         } else {
             ui.label("The fractal_clock clock is not showing the correct time");
         };
+        ui.label(format!("Painted line count: {}", self.line_count));
 
         ui.checkbox(&mut self.paused, "Paused");
         ui.add(Slider::f32(&mut self.zoom, 0.0..=1.0).text("zoom"));
@@ -128,13 +131,16 @@ impl FractalClock {
         ];
 
         let scale = self.zoom * rect.width().min(rect.height());
-        let paint_line = |points: [Pos2; 2], color: Color32, width: f32| {
+        let mut shapes: Vec<Shape> = Vec::new();
+        let mut paint_line = |points: [Pos2; 2], color: Color32, width: f32| {
             let line = [
                 rect.center() + scale * points[0].to_vec2(),
                 rect.center() + scale * points[1].to_vec2(),
             ];
 
-            painter.line_segment([line[0], line[1]], (width, color));
+            if rect.intersects(Rect::from_two_pos(line[0], line[1])) {
+                shapes.push(Shape::line_segment(line, (width, color)));
+            }
         };
 
         let hand_rotations = [
@@ -199,5 +205,7 @@ impl FractalClock {
 
             std::mem::swap(&mut nodes, &mut new_nodes);
         }
+        self.line_count = shapes.len();
+        painter.extend(shapes);
     }
 }

emath/src/rect.rs

@@ -91,6 +91,14 @@ impl Rect {
             max: pos2(*x_range.end(), *y_range.end()),
         }
     }
+    pub fn from_two_pos(a: Pos2, b: Pos2) -> Self {
+        let (left, right) = if a.x > b.x { (b.x, a.x) } else { (a.x, b.x) };
+        let (top, bottom) = if a.y > b.y { (b.y, a.y) } else { (a.y, b.y) };
+        Rect {
+            min: pos2(left, top),
+            max: pos2(right, bottom),
+        }
+    }
 
     /// Expand by this much in each direction, keeping the center
     #[must_use]