port: make the legal screen render correctly

also, total errno death in the same commit because I am dumb

port/fast3d/gfx_window_manager_api.h

@@ -0,0 +1,21 @@
+#ifndef GFX_WINDOW_MANAGER_API_H
+#define GFX_WINDOW_MANAGER_API_H
+
+#include <stdint.h>
+#include <stdbool.h>
+
+struct GfxWindowManagerAPI {
+    void (*init)(const char *game_name, bool start_in_fullscreen);
+    void (*set_fullscreen_changed_callback)(void (*on_fullscreen_changed)(bool is_now_fullscreen));
+    void (*set_fullscreen)(bool enable);
+    void (*main_loop)(void (*run_one_game_iter)(void));
+    void (*get_dimensions)(uint32_t *width, uint32_t *height);
+    void (*handle_events)(void);
+    bool (*start_frame)(void);
+    void (*swap_buffers_begin)(void);
+    void (*swap_buffers_end)(void);
+    double (*get_time)(void); // For debug
+    void *(*get_window_handle)(void);
+};
+
+#endif