Stronger liquid swell, flow along rivers, brighter lava and new lava texture

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

src/gfx.rs

@@ -622,19 +622,27 @@ fn gen_atlas() -> Image {
                 _ => shade((24, 50, 88), d),
             })
         });
-        // lava: glowing orange with dark crust plates (4x4 plates, seamless at the cell border)
+        // lava: molten orange with hot yellow streaks and darker red troughs, no black crust.
+        // Seamless (period 16) so it can flow across the tiles
         cv.cell(T_LAVA + v, |x, y| {
-            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))
-            } else if crust + edge > 0.7 {
-                Some(c(200, 60, 20))
-            } else if hash(x, y, v + 133) % 11 == 0 {
-                Some(c(255, 230, 120))
+            let tau = std::f32::consts::TAU;
+            let (fx, fy) = (x as f32 / 16.0, y as f32 / 16.0);
+            let o = v as f32 * 1.3;
+            let heat = (tau * (fx + fy * 2.0) + o).sin() * 0.45
+                + (tau * (fx * 3.0 - fy) + (tau * fy * 2.0 + o).sin() * 1.2).sin() * 0.35
+                + (tau * (fy * 3.0 + fx * 2.0) + o * 2.0).sin() * 0.2;
+            let d = (rnd(x, y, v + 134) * 16.0) as i32 - 8;
+            Some(if heat > 0.62 {
+                shade((255, 228, 120), d / 2)
+            } else if heat > 0.3 {
+                shade((255, 170, 55), d)
+            } else if heat > -0.35 {
+                shade((240, 110, 25), d)
+            } else if heat > -0.7 {
+                shade((200, 64, 18), d)
             } else {
-                Some(shade((250, 130, 30), (rnd(x, y, v + 134) * 30.0) as i32 - 15))
-            }
+                shade((150, 40, 14), d)
+            })
         });
         // knight fortress walls: pale stone blocks with blue-grey mortar
         cv.cell(T_FORTWALL + v, |x, y| {