Raise walls: plan them on own floor, imps build reinforced earth

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

src/gfx.rs

@@ -88,6 +88,7 @@ pub const T_CAP: u32 = 200; // giant mushroom cap, glowing spots
 pub const T_BARK: u32 = 201; // tree trunk
 pub const T_LEAVES: u32 = 202; // 2 variants: tree crown
 pub const T_GRASS: u32 = 204; // 4 variants: grass above ground
+pub const I_WALL: u32 = 208; // wall tool: bricks rising from the floor
 
 pub struct Gfx {
     pub atlas: Texture2D,
@@ -827,6 +828,20 @@ fn gen_atlas() -> Image {
             None
         }
     });
+    // wall tool icon: a block of bricks with an arrow up
+    cv.cell(I_WALL, |x, y| {
+        if (3..=12).contains(&x) && (6..=14).contains(&y) {
+            let row = (y - 6) / 3;
+            let joint = (y - 6) % 3 == 2 || (x + row * 3) % 6 == 0;
+            Some(if joint { c(60, 40, 30) } else { c(150, 100, 70) })
+        } else if y <= 4 && (x - 8).abs() <= 4 - y.max(1) + 1 && y >= 1 {
+            Some(c(200, 140, 255))
+        } else if y == 5 && (7..=9).contains(&x) {
+            Some(c(200, 140, 255))
+        } else {
+            None
+        }
+    });
     // frost spell icon: a snowflake
     cv.cell(I_FREEZE, |x, y| {
         let (dx, dy) = (x - 8, y - 8);