diff --git a/main.c b/main.c
index 9c6a898..6c35d6f 100644
--- a/main.c
+++ b/main.c
@@ -33,6 +33,7 @@
     #error "unknown pixel format"
 #endif
 
+/* state that must be accessible by libmgba camera callbacks */
 static SDL_Surface* scaled = NULL;
 static SDL_Surface* filtered[NUM_CHANNELS] = { NULL, NULL, NULL };
 
@@ -41,8 +42,10 @@ struct AppState {
     SDL_Window* window;
     SDL_Renderer* renderer;
 
+    /* indices used by SelectCamera */
     int cam_idx, spec_idx;
 
+    /* used by FlipCamera */
     SDL_CameraID front_camera;
     SDL_CameraID back_camera;
 
@@ -51,6 +54,7 @@ struct AppState {
     SDL_Surface* screens[NUM_CHANNELS];
     struct mCore* cores[NUM_CHANNELS];
 
+    /* GB button presses fed to mgba */
     unsigned keys;
 };