automatic detenction of texture mode and batching based on it

src/textures.h

@@ -2,6 +2,7 @@
 #define TEXTURES_H
 
 #include "private/textures.h"
+#include "textures/modes.h"
 #include "util.h"
 
 #include <SDL2/SDL.h>
@@ -45,6 +46,9 @@ int32_t textures_get_atlas_id(const struct texture_cache *cache, t_texture_key k
 /* binds atlas texture in opengl state */
 void textures_bind(const struct texture_cache *cache, t_texture_key key, GLenum target);
 
+/* returns helpful information about contents of alpha channel in given texture */
+enum texture_mode textures_get_mode(const struct texture_cache *cache, t_texture_key key);
+
 /* returns the number of atlases in the cache */
 size_t textures_get_num_atlases(const struct texture_cache *cache);