Simplify Langton.update

AllenDowney · AllenDowney · commit 096ebddffc6a · 2019-09-13T14:30:13.000-04:00
diff --git a/ch15/Conway.java b/ch15/Conway.java
@@ -13,14 +13,14 @@ public class Conway extends Automaton {
      */
     public Conway() {
         grid = new GridCanvas(30, 25, SIZE);
-        grid.flip(1, 2);
-        grid.flip(2, 2);
-        grid.flip(3, 2);
-        grid.flip(6, 1);
-        grid.flip(7, 2);
-        grid.flip(7, 3);
-        grid.flip(8, 1);
-        grid.flip(8, 2);
+        grid.getCell(1, 2).turnOn();
+        grid.getCell(2, 2).turnOn();
+        grid.getCell(3, 2).turnOn();
+        grid.getCell(6, 1).turnOn();
+        grid.getCell(7, 2).turnOn();
+        grid.getCell(7, 3).turnOn();
+        grid.getCell(8, 1).turnOn();
+        grid.getCell(8, 2).turnOn();
     }
 
     /**
@@ -71,7 +71,8 @@ public Conway(String path, int margin) {
             for (int c = 0; c < line.length(); c++) {
                 char x = line.charAt(c);
                 if (x == 'O') {
-                    grid.flip(r + margin, c + margin);
+                    Cell cell = grid.getCell(r + margin, c + margin);
+                    cell.turnOn();
                 }
             }
         }
diff --git a/ch15/GridCanvas.java b/ch15/GridCanvas.java
@@ -21,12 +21,14 @@ public GridCanvas(int rows, int cols, int size) {
         // build 2D array of cells
         array = new Cell[rows][cols];
         for (int r = 0; r < rows; r++) {
+        	int y = r * size;
             for (int c = 0; c < cols; c++) {
-                array[r][c] = new Cell(c * size, r * size, size);
+            	int x = c * size;
+                array[r][c] = new Cell(x, y, size);
             }
         }
 
-        // set up the canvas drawing
+        // set the canvas size
         setSize(cols * size, rows * size);
     }
 
@@ -53,17 +55,6 @@ public Cell getCell(int r, int c) {
         return array[r][c];
     }
 
-    /**
-     * Toggles the cell on/off.
-     * 
-     * @param r row index
-     * @param c column index
-     */
-    public void flip(int r, int c) {
-        Cell cell = array[r][c];
-        cell.flip();
-    }
-
     /**
      * Returns 1 if the cell at (r, c) exists and is on. Returns 0 if the cell
      * doesn't exist or is off.
diff --git a/ch15/Langton.java b/ch15/Langton.java
@@ -26,17 +26,11 @@ public void update() {
         if (cell.isOn()) {
             // at a black square; flip color and turn left
             cell.turnOff();
-            head -= 1;
-            if (head < 0) {
-                head = 3;
-            }
+            head = (head + 3) % 4;
         } else {
             // at a white square; flip color and turn right
             cell.turnOn();
-            head += 1;
-            if (head > 3) {
-                head = 0;
-            }
+            head = (head + 1) % 4;
         }
 
         // move forward one unit
@@ -57,6 +51,8 @@ public void update() {
 
         // update the display
         grid.repaint();
+        
+        // TODO: draw a triangle to show the ant
     }
 
 }
diff --git a/ch15/Main.java b/ch15/Main.java
@@ -13,7 +13,8 @@ public class Main {
      */
     public static void main(String[] args) {
         String title = "Conway's Game of Life";
-        Automaton game = new Conway("pulsar.cells", 2);
+        Automaton game = new Conway();
+        // Automaton game = new Conway("pulsar.cells", 2);
         runSimulation(title, game, 500);
     }
 

Original file line number	Diff line number	Diff line change
`@@ -13,7 +13,8 @@ public class Main {`
`13`	`13`	`*/`
`14`	`14`	`public static void main(String[] args) {`
`15`	`15`	`String title = "Conway's Game of Life";`
`16`		`- Automaton game = new Conway("pulsar.cells", 2);`
	`16`	`+ Automaton game = new Conway();`
	`17`	`+ // Automaton game = new Conway("pulsar.cells", 2);`
`17`	`18`	`runSimulation(title, game, 500);`
`18`	`19`	`}`
`19`	`20`