Growable pixels

Author: nint8835

frontend/src/components/PropertyEditor.svelte

@@ -2,6 +2,8 @@
     import { store } from '../game';
 
     const propertyDescriptions: Record<number, string> = {
+        16: 'Grows',
+        23: 'Causes growth',
         24: 'Floats',
         32: 'Enable gravity',
     };

src/conjam.gleam

@@ -2,6 +2,7 @@ import brush.{apply_brush}
 import canvas
 import constants.{max_x, max_y}
 import gravity.{apply_gravity}
+import growth.{apply_growth}
 
 pub fn draw_frame(
   frame_number: Int,
@@ -46,6 +47,7 @@ fn iter_pixels(
     _, _ -> {
       let new_frame_data =
         frame_data
+        |> apply_growth(x, y, next_pixel_offset)
         |> apply_gravity(x, y, next_pixel_offset)
 
       iter_pixels(new_frame_data, x + next_pixel_offset, y, next_pixel_offset)

src/growth.gleam

@@ -0,0 +1,71 @@
+import canvas
+import constants.{max_x, max_y}
+import gleam/bool
+import properties
+
+pub fn apply_growth(
+  image_data: canvas.ImageData,
+  x: Int,
+  y: Int,
+  next_pixel_offset: Int,
+) -> canvas.ImageData {
+  use <- canvas.ensure_pixel_exists(image_data, x, y)
+
+  let pixel_val = canvas.get_pixel(image_data, x, y)
+
+  use <- bool.guard(when: pixel_val == 0x00000000, return: image_data)
+  use <- bool.guard(
+    when: !properties.has_property(pixel_val, properties.grows),
+    return: image_data,
+  )
+
+  let next_x = x + next_pixel_offset
+
+  let next_pixel_val = case next_x < 0 || next_x > max_x {
+    True -> 0x00000000
+    False -> canvas.get_pixel(image_data, next_x, y)
+  }
+
+  let next_pixel_causes_growth =
+    properties.has_property(next_pixel_val, properties.causes_growth)
+
+  case next_pixel_causes_growth {
+    True -> {
+      image_data
+      |> canvas.set_pixel(next_x, y, pixel_val)
+    }
+    False -> {
+      let above_pixel_val = case y + 1 > max_y {
+        True -> 0x00000000
+        False -> canvas.get_pixel(image_data, x, y + 1)
+      }
+
+      let above_pixel_causes_growth =
+        properties.has_property(above_pixel_val, properties.causes_growth)
+
+      case above_pixel_causes_growth {
+        True -> {
+          image_data
+          |> canvas.set_pixel(x, y + 1, pixel_val)
+        }
+        False -> {
+          let below_pixel_val = case y - 1 < 0 {
+            True -> 0x00000000
+            False -> canvas.get_pixel(image_data, x, y - 1)
+          }
+
+          let below_pixel_causes_growth =
+            properties.has_property(below_pixel_val, properties.causes_growth)
+
+          case below_pixel_causes_growth {
+            True -> {
+              image_data
+              |> canvas.set_pixel(x, y - 1, pixel_val)
+            }
+            False -> image_data
+          }
+        }
+      }
+    }
+  }
+}

src/properties.gleam

@@ -1,5 +1,11 @@
 import gleam/int
 
+// 00000000 00000001 00000000 00000000
+pub const grows = 0x00010000
+
+// 00000000 00000000 00000010 00000000
+pub const causes_growth = 0x00000200
+
 // 00000000 00000000 00000001 00000000
 pub const floats = 0x00000100