use texture array instead of atlas for tiles

src/scenes/shader/tile_frag.glsl

@@ -1,9 +1,11 @@
 #version 150
 
+#define MILLIS_PER_TILE 4000u
+
 in vec2 v_uv;
 flat in uint v_tileidx;
 out vec4 pixcolor;
-uniform sampler2D t_atlas;
+uniform sampler2DArray t_tiles;
 uniform b_constants {
   uvec4 anim;
   float R1;
@@ -19,8 +21,8 @@ uniform b_locals {
 void main() {
   vec2 anim_uv = v_uv;
   if (v_tileidx < 128u && bool(anim[v_tileidx / 32u] & 1u << v_tileidx % 32u)) {
-    anim_uv = vec2(v_uv.x, float((uint(v_uv.y * 1000.0) + millis / 4u) % 1000u) / 1000.0);
+    anim_uv = vec2(v_uv.x, v_uv.y + float(millis % MILLIS_PER_TILE) / MILLIS_PER_TILE);
   }
-  vec2 uv = vec2(anim_uv.x, float(v_tileidx) / 256.0 + (1.0 - anim_uv.y) / 256.0);
-  pixcolor = texture(t_atlas, uv);
+
+  pixcolor = texture(t_tiles, vec3(anim_uv.x, 1.0 - anim_uv.y, v_tileidx));
 }