## High level overview

Under the hood every element has an id, this id allows the library to store state
between frames. 
Elements are also cached such that when the ui tree is rebuilt at the beginning of 
every frame the element data structure doesn't have to be rebuilt.

Elements are arranged in a tree, nodes are container elements that can contain other
elements, leafs are elements that cannot contain other elements.

Every element has a size and a position, containers also have to keep track of their
layout information and some other state.

Elements can push commands into the draw stack, which is a structure that contains 
all the draw commands that the user application has to perform do display the ui
correctly, such commands include drawing lines, rectangles, sprites, text, etc.


```text
            +-----------+
            | ug_init() |
            +-----+-----+
                  |
                  |
                  |
        +---------v----------+
        |ug_input_keyboard() |
        |ug_input_mouse()    <----+
        |ug_input_clipboard()|    |
        |        ...         |    |
        +---------+----------+    |
                  |               |
                  |               |
          +-------v--------+      |
          |ug_frame_begin()|      |
          +-------+--------+      |
                  |               |
                  |               |
        +---------v----------+    |
        |ug_window_start()   |    |
   +---->ug_container_start()|    |
   |    |ug_div_start()      |    |
   |    |        ...         |    |
   |    +---------+----------+    |
   |              |               |
   |              |               |
multiple +--------v---------+     |
 times   |ug_layout_row()   |     |
   |     |ug_layout_column()|     |
   |     |ug_layout_float() |     |
   |     |       ...        |     |
   |     +--------+---------+     |
   |              |               |
   |              |               |
   |       +------v------+        |
   |       |ug_button()  |        |
   |       |ug_text_box()|        |
   |       |ug_slider()  |        |
   |       |     ...     |        |
   |       +------+------+        |
   |              |               |
   +--------------+               |
                  |               |
         +--------v---------+     |
         |ug_window_end()   |     |
         |ug_container_end()|     |
         |ug_div_end()      |     |
         |       ...        |     |
         +--------+---------+     |
                  |               |
                  |               |
                  |               |
           +------v-------+       |
           |ug_frame_end()|       |
           +------+-------+       |
                  |               |
                  |               |
                  |               |
           +------v-------+       |
           |user draws the|       |
           |      ui      +-------+
           +------+-------+
                  |
                  |quit
                  |
           +------v-------+
           | ug_destroy() |
           +--------------+
```

### Notes

How elements determine if they have focus or not

```C
// in begin_{container} code
calculate focus
set has_focus property



// in the element code
if(PARENT_HAS_FOCUS()) {
	update stuff
} else {
	fast path to return 
}
```