Animate water and lava with gentle waves and flowing textures

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

src/gfx.rs

@@ -609,9 +609,12 @@ fn gen_atlas() -> Image {
     });
     // ---- campaign terrain
     for v in 0..4u32 {
-        // water: dark blue with lighter wave crests
+        // water: dark blue with lighter wave crests. Seamless (period 16): the shader lets it flow
+        // across the tiles, sampled in world space
         cv.cell(T_WATER + v, |x, y| {
-            let wave = ((x as f32 * 0.8 + (y as f32 * 0.9 + v as f32 * 1.7).sin() * 2.2) as i32 + y * 2) % 9;
+            let tau = std::f32::consts::TAU;
+            let bend = ((y as f32 + v as f32 * 3.0) * tau / 16.0).sin() * 1.6 + ((x as f32) * tau / 8.0).sin() * 0.6;
+            let wave = (x + y * 2 + bend.round() as i32).rem_euclid(8);
             let d = (rnd(x, y, v + 120) * 10.0) as i32 - 5;
             Some(match wave {
                 0 => shade((70, 120, 170), d),
@@ -619,9 +622,9 @@ fn gen_atlas() -> Image {
                 _ => shade((24, 50, 88), d),
             })
         });
-        // lava: glowing orange with dark crust plates
+        // lava: glowing orange with dark crust plates (4x4 plates, seamless at the cell border)
         cv.cell(T_LAVA + v, |x, y| {
-            let crust = rnd(x / 3 + (y / 3) % 2, y / 3, v + 130);
+            let crust = rnd((x / 4 + (y / 4) % 2) % 4, y / 4, v + 130);
             let edge = rnd(x, y, v + 131) * 0.25;
             if crust + edge > 0.85 {
                 Some(shade((60, 22, 14), (rnd(x, y, v + 132) * 14.0) as i32))