refactor: Spread game code into modular files for better maintainability

This commit reorganizes the game's source code into multiple files within a `js/` directory, creating a more modular and maintainable structure. The changes include:

- Created separate files for different game components:
  - `constants.js`: Game constants and element types
  - `world.js`: World management functions
  - `terrain.js`: Terrain generation logic
  - `physics.js`: Physics simulation
  - `render.js`: Rendering functions
  - `input.js`: Input handling
  - `main.js`: Main game initialization and loop
  - Element-specific files in `js/elements/`:
    - `basic.js`: Sand, water, dirt behaviors
    - `plants.js`: Grass, seeds, flowers
    - `trees.js`: Tree growth and leaf generation
    - `fire.js`: Fire and lava behaviors

- Updated `index.html` to load modules in the correct order
- Removed the monolithic `script.js`

The modular approach improves code readability, makes future extensions easier, and separates concerns more effectively.

js/elements/plants.js

@@ -0,0 +1,159 @@
+// Plant element behaviors (grass, seeds, trees)
+function updateGrass(x, y) {
+    // Grass behaves like dirt for physics
+    if (getPixel(x, y + 1) === EMPTY) {
+        setPixel(x, y, EMPTY);
+        setPixel(x, y + 1, GRASS);
+    } 
+    else if (getPixel(x - 1, y + 1) === EMPTY) {
+        setPixel(x, y, EMPTY);
+        setPixel(x - 1, y + 1, GRASS);
+    } 
+    else if (getPixel(x + 1, y + 1) === EMPTY) {
+        setPixel(x, y, EMPTY);
+        setPixel(x + 1, y + 1, GRASS);
+    }
+    else if (getPixel(x, y + 1) === WATER) {
+        setPixel(x, y, WATER);
+        setPixel(x, y + 1, GRASS);
+    }
+    
+    // Grass can spread to nearby dirt
+    if (Math.random() < 0.0005) {
+        const directions = [
+            {dx: -1, dy: 0}, {dx: 1, dy: 0}, 
+            {dx: 0, dy: -1}, {dx: 0, dy: 1}
+        ];
+        
+        const dir = directions[Math.floor(Math.random() * directions.length)];
+        if (getPixel(x + dir.dx, y + dir.dy) === DIRT) {
+            setPixel(x + dir.dx, y + dir.dy, GRASS);
+        }
+    }
+    
+    // Grass dies if covered (no air above)
+    if (getPixel(x, y - 1) !== EMPTY && Math.random() < 0.05) {
+        setPixel(x, y, DIRT);
+    }
+}
+
+function updateSeed(x, y) {
+    // Seeds fall like sand
+    if (getPixel(x, y + 1) === EMPTY) {
+        setPixel(x, y, EMPTY);
+        setPixel(x, y + 1, SEED);
+        moveMetadata(x, y, x, y + 1);
+    } 
+    else if (getPixel(x - 1, y + 1) === EMPTY) {
+        setPixel(x, y, EMPTY);
+        setPixel(x - 1, y + 1, SEED);
+        moveMetadata(x, y, x - 1, y + 1);
+    } 
+    else if (getPixel(x + 1, y + 1) === EMPTY) {
+        setPixel(x, y, EMPTY);
+        setPixel(x + 1, y + 1, SEED);
+        moveMetadata(x, y, x + 1, y + 1);
+    }
+    // Seeds can float on water
+    else if (getPixel(x, y + 1) === WATER) {
+        // Just float, don't do anything
+    }
+    // If seed is on dirt or grass, it can germinate
+    else if (getPixel(x, y + 1) === DIRT || getPixel(x, y + 1) === GRASS) {
+        const metadata = getMetadata(x, y);
+        
+        // Check if this is a flower seed
+        if (metadata && metadata.type === 'flower') {
+            setPixel(x, y, FLOWER);
+            // Set a random flower color
+            setMetadata(x, y, { 
+                type: 'flower',
+                color: FLOWER_COLORS[Math.floor(Math.random() * FLOWER_COLORS.length)],
+                age: 0,
+                height: 1
+            });
+        } else {
+            // Regular seed becomes a grass blade
+            setPixel(x, y, GRASS_BLADE);
+            setMetadata(x, y, { age: 0, height: 1 });
+        }
+    }
+}
+
+function updateGrassBlade(x, y) {
+    // Grass blades are static once grown
+    const metadata = getMetadata(x, y);
+    
+    if (!metadata) {
+        setMetadata(x, y, { age: 0, height: 1 });
+        return;
+    }
+    
+    // Increment age
+    metadata.age++;
+    setMetadata(x, y, metadata);
+    
+    // Grass blades can grow taller up to a limit
+    if (metadata.age % 200 === 0 && metadata.height < 3 && getPixel(x, y - 1) === EMPTY) {
+        setPixel(x, y - 1, GRASS_BLADE);
+        setMetadata(x, y - 1, { age: 0, height: metadata.height + 1 });
+        metadata.isTop = false;
+        setMetadata(x, y, metadata);
+    }
+    
+    // Grass blades die if covered by something other than another grass blade
+    if (getPixel(x, y - 1) !== EMPTY && getPixel(x, y - 1) !== GRASS_BLADE && Math.random() < 0.01) {
+        setPixel(x, y, EMPTY);
+        removeMetadata(x, y);
+    }
+}
+
+function updateFlower(x, y) {
+    // Flowers are similar to grass blades but with a colored top
+    const metadata = getMetadata(x, y);
+    
+    if (!metadata) {
+        setMetadata(x, y, { 
+            type: 'flower',
+            color: FLOWER_COLORS[Math.floor(Math.random() * FLOWER_COLORS.length)],
+            age: 0,
+            height: 1
+        });
+        return;
+    }
+    
+    // Increment age
+    metadata.age++;
+    setMetadata(x, y, metadata);
+    
+    // Flowers can grow taller up to a limit (2x bigger)
+    if (metadata.age % 300 === 0 && metadata.height < 8 && getPixel(x, y - 1) === EMPTY) {
+        // If this is the top of the flower, make it a stem and put a new flower on top
+        setPixel(x, y - 1, FLOWER);
+        setMetadata(x, y - 1, { 
+            type: 'flower',
+            color: metadata.color,
+            age: 0,
+            height: metadata.height + 1,
+            isTop: true
+        });
+        metadata.isTop = false;
+        setMetadata(x, y, metadata);
+    }
+    
+    // Flowers die if covered
+    if (getPixel(x, y - 1) !== EMPTY && getPixel(x, y - 1) !== FLOWER && Math.random() < 0.01) {
+        setPixel(x, y, EMPTY);
+        removeMetadata(x, y);
+    }
+    
+    // Flowers can drop seeds occasionally
+    if (metadata.isTop && Math.random() < 0.0001) {
+        const directions = [-1, 1];
+        const dir = directions[Math.floor(Math.random() * directions.length)];
+        if (getPixel(x + dir, y) === EMPTY) {
+            setPixel(x + dir, y, SEED);
+            setMetadata(x + dir, y, { type: 'flower' });
+        }
+    }
+}