1 files changed, 94 insertions, 0 deletions
diff --git a/src/utils/fov.c b/src/utils/fov.c
new file mode 100644
index 0000000..3d5ae16
--- /dev/null
+++ b/src/utils/fov.c
@@ -0,0 +1,94 @@
+#include <engine/fov.h>
+#include <engine/utils.h>
+#include <math.h>
+#include <stdint.h>
+
+void fov_shadowcast_rec(const void* map, const v2_i32 mapsize,
+                        bool (*visblocking)(const void*), i32* lightmap,
+                        const i32 range, v2_i32 src, const i32 row, f32 start,
+                        const f32 end, const i8 xx, const i8 xy, const i8 yx,
+                        const i8 yy) {
+
+  if (start < end) return;
+
+  const i32 range_2 = range * range;
+  f32 new_start = start;
+
+  for (i32 i = row; i <= range; i++) {
+    i32 dx = (-1 * i) - 1;
+    i32 dy = -1 * i;
+
+    bool blocked = false;
+
+    while (dx <= 0) {
+      dx += 1;
+
+      const i32 mapx = src.x + dx * xx + dy * xy;
+      const i32 mapy = src.y + dx * yx + dy * yy;
+
+      const f32 slope_l = (((f32)dx) - 0.5f) / (((f32)dy) + 0.5f);
+      const f32 slope_r = (((f32)dx) + 0.5f) / (((f32)dy) - 0.5f);
+
+      if (start < slope_r) continue;
+      if (end > slope_l) break;
+
+      if (dx * dx + dy * dy < range_2) {
+        /* set as visible */
+        if (mapx >= 0 && mapx < (long)mapsize.x && mapy >= 0 &&
+            mapy < (long)mapsize.y) {
+          // TODO: Calculate proper dist from source
+          f32 x_2 = (src.x - mapx) * (src.x - mapx);
+          f32 y_2 = (src.y - mapy) * (src.y - mapy);
+          lightmap[mapy * mapsize.x + mapx] =
+              MAX(lightmap[mapy * mapsize.x + mapx],
+                  range - sqrt((f32)(x_2 + y_2)));
+        }
+      }
+
+      /* sizeof(i32) is the size of enums */
+      /* -- unless the compiler doesn't follow standard behaviour */
+      const bool is_blocked = visblocking(
+          (void*)((u64)map + sizeof(i32)                     /* ~ enum size */
+                                 * (mapsize.x * mapy + mapx) /* index */
+                  ));
+
+      if (blocked) {
+        if (!is_blocked) {
+          new_start = slope_r;
+        } else {
+          blocked = false;
+          start = new_start;
+        }
+      } else if (!is_blocked && i < range) {
+        blocked = true;
+        fov_shadowcast_rec(map, mapsize, visblocking, lightmap, range, src,
+                           i + 1, start, slope_l, xx, xy, yx, yy);
+        new_start = slope_r;
+      }
+    }
+
+    if (blocked) break;
+  }
+}
+
+/* http://www.roguebasin.com/index.php?title=FOV_using_recursive_shadowcasting
+ */
+void fov_shadowcast(const void* map, const v2_i32 mapsize,
+                    bool (*visblocking)(const void*), i32* lightmap,
+                    const i32 range, const v2_i32 src) {
+
+  const i8 m[4][8] = {
+      {1, 0, 0, -1, -1, 0, 0, 1},
+      {0, 1, -1, 0, 0, -1, 1, 0},
+      {0, 1, 1, 0, 0, -1, -1, 0},
+      {1, 0, 0, 1, -1, 0, 0, -1},
+  };
+
+  for (i32 oct = 0; oct < 8; oct++) {
+    fov_shadowcast_rec(map, mapsize, visblocking, lightmap, range, src, 1, 1.0,
+                       0.0, m[0][oct], m[1][oct], m[2][oct], m[3][oct]);
+  }
+
+  /* The center is the most lit square */
+  lightmap[src.y * mapsize.x + src.x] = range;
+}