Improve automata slide.

src/slide/s4_automata.rs

@@ -156,25 +156,37 @@ impl Slide for Automata {
             } => {
                 // Iterate grid ~5 times a second.
                 if self.governor.ready(ui.ctx().input().time, 0.2) {
-                    if *iterations == 10 {
-                        // Automatically begin expansion.
-                        *expanding = true;
-                    } else if *iterations == 20 {
-                        // Draw a vertical line on the left to create a cool pattern.
-                        for y in 4..self.life.size_cells - 4 {
-                            self.life.set_fill(2, y, Color32::BLACK);
+                    // Schedule some special events at some interation counts.
+                    match *iterations {
+                        10 => {
+                            // Automatically begin expansion.
+                            *expanding = true;
                         }
-                    } else if *iterations == 30 {
-                        // Draw another set of lines to create a cool pattern.
-                        for x in 4..self.life.size_cells - 4 {
-                            // Solid line at the bottom.
-                            self.life
-                                .set_fill(x, self.life.size_cells - 2, Color32::BLACK);
-                            // Line with gaps at the top.
-                            if x % 6 != 0 {
-                                self.life.set_fill(x, 2, Color32::BLACK);
+                        20 => {
+                            for y in 4..self.life.size_cells - 4 {
+                                // Line on the left.
+                                self.life.set_fill(2, y, Color32::BLACK);
+
+                                // Line with gaps on the right.
+                                if y < self.life.size_cells - 11 && y % 8 != 0 {
+                                    self.life
+                                        .set_fill(self.life.size_cells - 2, y, Color32::BLACK);
+                                }
+                            }
+                        }
+                        30 => {
+                            // Draw another set of lines to create a cool pattern.
+                            for x in 4..self.life.size_cells - 4 {
+                                // Solid line at the bottom.
+                                self.life
+                                    .set_fill(x, self.life.size_cells - 2, Color32::BLACK);
+                                // Line with gaps at the top.
+                                if x % 6 != 0 {
+                                    self.life.set_fill(x, 2, Color32::BLACK);
+                                }
                             }
                         }
+                        _ => {}
                     }
 
                     // Boolean to int cast yields 1 if true, 0 otherwise.