Improve automata slide.

src/component/grid.rs

@@ -145,7 +145,7 @@ impl Grid {
 
                 let cell_width = 1.0 / self.size_cells as f32;
                 // Make sure neighboring cells overlap without gaps.
-                let tolerance = 0.001;
+                let tolerance = 0.0008;
                 for y in 0..self.size_cells {
                     let y_coord = y as f32 / self.size_cells as f32;
                     for x in 0..self.size_cells {

src/slide/s4_automata.rs

@@ -40,8 +40,8 @@ enum AutomataState {
     },
     /// Simulation.
     Life {
-        /// Whether we started expanding the grid yet.
-        expanding: bool,
+        /// Whether we inverted the color and turned on fading yet.
+        rule_changed: bool,
         /// Conway iteration counter.
         iterations: usize,
     },
@@ -95,17 +95,17 @@ impl Slide for Automata {
                     *rules = Some(ctx.input().time)
                 } else {
                     self.state = AutomataState::Life {
-                        expanding: false,
+                        rule_changed: false,
                         iterations: 0,
                     };
                 }
             }
-            AutomataState::Life { expanding, .. } => {
-                if *expanding {
+            AutomataState::Life { rule_changed, .. } => {
+                if !*rule_changed {
+                    *rule_changed = true;
+                } else {
                     // Done with the slide.
                     return true;
-                } else {
-                    *expanding = true;
                 }
             }
         }
@@ -146,17 +146,14 @@ impl Slide for Automata {
                 }
             }
             AutomataState::Life {
-                expanding,
+                rule_changed,
                 iterations,
             } => {
                 // Iterate grid ~5 times a second.
                 if self.governor.ready(ui.ctx().input().time, 0.2) {
                     // Schedule some special events at some iteration counts.
+                    let expanding = *iterations >= 10;
                     match *iterations {
-                        10 => {
-                            // Automatically begin expansion.
-                            *expanding = true;
-                        }
                         20 => {
                             for y in 4..self.life.size_cells - 4 {
                                 // Line on the left.
@@ -185,8 +182,17 @@ impl Slide for Automata {
                     }
 
                     // Boolean to int cast yields 1 if true, 0 otherwise.
-                    let expansion = (*expanding && self.life.size_cells < 64) as usize;
-                    self.life = conways_game_of_life(&self.life, expansion);
+                    let expansion = (expanding && self.life.size_cells < 64) as usize;
+
+                    // Implement rule changes.
+                    let (background_color, alive_color, stroke_color, fade) = if *rule_changed {
+                        (Color32::BLACK, Color32::WHITE, Color32::TRANSPARENT, true)
+                    } else {
+                        (Color32::TRANSPARENT, Color32::BLACK, Color32::GRAY, false)
+                    };
+                    self.life.background = background_color;
+                    self.life.stroke = stroke_color;
+                    self.life = conways_game_of_life(&self.life, expansion, alive_color, fade);
                     *iterations += 1;
                 }
 
@@ -251,7 +257,7 @@ impl Slide for Automata {
 /// Run one iteration of Conway's Game of Life on the grid, producing a new grid.
 ///
 /// A non-zero expansion parameter expands the grid on each side by that many squares.
-fn conways_game_of_life(grid: &Grid, expansion: usize) -> Grid {
+fn conways_game_of_life(grid: &Grid, expansion: usize, alive_color: Color32, fade: bool) -> Grid {
     let mut new = grid.clone();
     new.clear_fill();
 
@@ -271,15 +277,15 @@ fn conways_game_of_life(grid: &Grid, expansion: usize) -> Grid {
                         // Don't consider self.
                         continue;
                     }
-                    if grid.fill(x, y).a() > 0 {
+                    if grid.fill(x, y).is_opaque() {
                         neighbors += 1;
                     }
                 }
             }
 
-            let mut alive = grid.fill(cx, cy).a() > 0;
+            let was_alive = grid.fill(cx, cy).is_opaque();
 
-            alive = match (alive, neighbors) {
+            let alive = match (was_alive, neighbors) {
                 (false, 3) => true,
                 (false, _) => false,
                 (true, 2) | (true, 3) => true,
@@ -291,9 +297,13 @@ fn conways_game_of_life(grid: &Grid, expansion: usize) -> Grid {
                 cx + expansion,
                 cy + expansion,
                 if alive {
-                    Color32::BLACK
-                } else {
+                    alive_color
+                } else if !fade {
                     Color32::TRANSPARENT
+                } else {
+                    // Fade out gradually.
+                    let previous_alpha = grid.fill(cx, cy).a();
+                    set_alpha(alive_color, previous_alpha as f32 / (255.0 * 2.0))
                 },
             );
         }