make face culling optional

src/rendering/twn_gl_15_rendering.c

@@ -96,7 +96,11 @@ static void finally_use_space_pipeline(void) {
             if (GLAD_GL_ARB_depth_clamp)
                 glDisable(GL_DEPTH_CLAMP);
 
-            glEnable(GL_CULL_FACE);
+            if (ctx.cull_faces)
+                glEnable(GL_CULL_FACE);
+            else
+                glDisable(GL_CULL_FACE);
+
             glEnable(GL_TEXTURE_2D);
             glActiveTexture(GL_TEXTURE0);
             glEnable(GL_DEPTH_TEST);

src/twn_engine_context_c.h

@@ -81,6 +81,7 @@ typedef struct EngineContext {
     /* signals mouse focus, used to disable mouse capture */
     bool window_mouse_resident;
     bool audio_initialized;
+    bool cull_faces;
 } EngineContext;
 
 /* TODO: does it need to be marked with TWN_API? */

src/twn_loop.c

@@ -596,6 +596,13 @@ static bool initialize(void) {
             }
         }
         SDL_free(datum_font_filtering.u.s);
+
+        toml_datum_t datum_cull_faces = toml_bool_in(engine, "cull_faces");
+        if (!datum_cull_faces.ok) {
+            ctx.cull_faces = true;
+        } else {
+            ctx.cull_faces = datum_cull_faces.u.b;
+        }
     }
 
     /* these are dynamic arrays and will be allocated lazily by stb_ds */