rework to context: now there's engine and user code copies, renaming of fields, most things that shouldn't be there are hidden

src/twn_engine_context_c.h

@@ -17,6 +17,8 @@
 
 typedef struct EngineContext {
     /* user code facing context */
+    Context game_copy;
+    /* engine-side context, copied to `game_copy` before every frame */
     Context game;
 
     InputState input;
@@ -27,6 +29,8 @@ typedef struct EngineContext {
     /* where the app was run from, used as the root for packs */
     char *base_dir;
 
+    Vec2i window_dims;
+
     /* configuration */
     toml_table_t *config_table;
     int64_t base_render_width;
@@ -52,6 +56,7 @@ typedef struct EngineContext {
     uint8_t audio_stream_channel_count;
 
     /* main loop machinery */
+    int64_t delta_time; /* preserves real time frame delta with no manipilation */
     int64_t clocks_per_second;
     int64_t prev_frame_time;
     int64_t desired_frametime;  /* how long one tick should be */
@@ -59,10 +64,17 @@ typedef struct EngineContext {
     int64_t delta_averager_residual;
     int64_t time_averager[4];
 
+    /* this should be a multiple of the current ticks per second */
+    /* use it to simulate low framerate (e.g. at 60 tps, set to 2 for 30 fps) */
+    /* it can be changed at runtime; any resulting logic anomalies are bugs */
+    uint32_t update_multiplicity;
+
     SDL_GLContext *gl_context;
     SDL_Window *window;
     uint32_t window_id;
 
+    bool is_running;
+    bool window_size_has_changed;
     bool resync_flag;
     bool was_successful;
 } EngineContext;