Shortlist
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[x] let pass flat args in ui_size_push() and ui_box_set_size()
[x] separate style stacks
[x] animation time stack
[>] margins? as part of size, or different styling stack?

[ ] Let build code set target style directly, and animate from current to target
[ ] filter styles stack by tag
[ ] image backgrounds/gradients?
[ ] animating open/close widgets?

[.] Text box widget
	[ ] Draw selection
	[ ] Set cursor on click
	[ ] Scroll to cursor

Canvas Drawing
--------------
[.] Correctly handle resizing / viewport
	[x] associate surfaces with mp_windows
	[x] window resize resizes surface. Surface always renders to whole mp_window
	[x] Add ability to create sub-views, and create surfaces for these
		- window comes with a main view, so we can get a surface for the whole window
	[>] Clean native mp_window_data struct (don't need to cache a lot of stuff here)

[.] Add images bliting
	[x] Clean, rename uv vs texUV stuff
	[>] Destroy stuff
	[>] More unified handle system
	[.] Rounded images (sortof)
	[ ] path clipped images

[ ] Add color gradients?
[ ] Make canvas implicit?
[/] Handle based error signaling
[/] Allow polling events in main thread, and updating/rendering in background thread.

[x] font metrics shouldn't depend on surface, & font
    shouldn't really depend on canvas either???
	> meaning we should be able to pass fonts without canvas in ui
	> and only pass canvas when drawing at the end...

UI
--
[x] Make gui context implicit?
[x] Uniform ui_box struct + cache widgets
[x] Prune unused boxes
[.] Layout boxes
	[x] basic two pass layout
	[x] Layout from start or end
	[>] Add overflow flags to layout, & solve conflicts

[x] Temporarily push transform and text flip when rendering UI, so that the coord system is y down, origin at top left
[x] Canvas render the same size on a high-dpi surface
	> it works with abstract 'pixel' units, which are transformed to pixels in the shader, according to backing store scaling

[.] Style struct and style stack
	[ ] Maybe use individual stack for different style attributes
[x] Pass initial style in ui_begin_frame()

[.] Draw boxes
	[x] use flags to enable/disable drawing each feature
	[ ] active/hovered transitions

[x] Change input state handling a move it to app layer
[x] Compute signals for ui_box
[x] Use ui_size_push() and pass axis instead of ui_width/height_push()
[>] Use value is ui_size as margin when kind == text or == children?

[ ] Allow animating sizes according to hot/active?

[ ] Basic helpers
	[.] button
	[.] slider (or rather, scroll bar)
	[.] simple spacers
		[ ] have a flag for non-cached stuff
	[.] scrolling panel
		[ ] Allow/disallow scrolling in x/y
		[ ] Scroll with mousewheel
		[/] add margins to scrollbars (disallow scrollbars crossing)

[?] Maybe let builder code handle "active"/"hot" state, since it
    depends on the widgets
    [ ] On the other hand, this state must be set before layouting, in
        particular font/fontSize -> maybe do a pass for static layout,
        instead of doing it in box creation...
    [ ] this way we can compute styling after user has set active/hot, but before layout
	> Maybe just let user set style selector, and provide persistent state bits that can
	> be used in any way? (to replace eg active/hot?) or perhaps not needed if we have just
	> 'dragging' state


[x] Mask mouse outside of parent rects -> maintain clip stack and clip mouse against it
[x] Mask mouse below panels/other widgets
[x] popups and tooltips
	[x] allow pushing/popping boxes irrespective of parent/child relation
	[x] ui_begin_frame() prepares two containers, user ui goes in the first one
	[x] tooltips and menus go to the second one
	[x] Add menus
[ ] line editing widget

Misc
----
[x] Split metal surface and metal painter (but put them in the same compilation unit?)
[x] Have only one rect struct
[x] Shorten mp_string to str8

[ ] Better/Simpler time API

[/] Frame throttling
	[x] For now, we always wait on vblank during mg_surface_present(), regardless of target fps
	[ ] Then actually get the correct display interval from the surface's current monitor
	[ ] Allow waiting for more display interval than one? (ie allow throttling at 30fps for a 60fps display)

[/] split osx_app and move all platform independant stuff outside

[ ] Sort out mg_matrix_push/pop() -> transform vs. set...