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Subject: Re: RFC new line API

Re: RFC new line API

From: Thomas Martitz <>
Date: Tue, 05 Mar 2013 23:59:00 +0100

Am 20.02.2013 13:33, schrieb Jonathan Gordon:
> On 20 February 2013 22:34, Thomas Martitz <
> <>> wrote:
> I start with list.c because that's the most extensive user, but
> other screens can follow easily, e.g. various plugins. The API
> that I suggest can print the whole line (indent, spacing, icon and
> text) in a single call so it's generally attractive.
> Ignoring plugins, 99% of the UI is drawn by list.c, so yes adding
> API's for its use would seem attractive, but that will almost
> certainly end up being wasted effort. I'm really aiming to have the
> lists entirely drawn by the skin engine by the next release which
> would make any effort here redundant.

Why should plugins be ignored. We should make things easier for them,
not harder, shouldn't we? Also I think the skin engine can use this API
as well, even if not to the full extend, as I want to use it to simplify
scrolling at a higher level. Also, the skin engine still needs a method
to draw styles and multi-line stuff which is not yet in place. I don't
see this effort as wasted.

> So, in that spirit I'd advocate you just doing the semi-nasty hack and
> adding a bit to the style flags so the scroller can redraw the
> seperater line (or just piggy-back off the gradient num_lines bits).
> Once the skin engine is doing the list drawing the scroller can be
> returned to a dumb text drawer (all line decorations would be drawn
> onto the backdrop buffer so the scroller clearing the line would leave
> them intact.)
> If all you want is a line separator then why is it not a
> simple 1 line lcd_hline() call in the draw_list() loop?
> This is what the current version on gerrit does. The problem is
> that scrolling breaks it (the scroll engine redraws the line
> selector which clears the separator). And it sucks from a
> software-architecture POV: The line selector is currently drawn in
> firmware, the separator would be drawn in apps (in this scenario).
> So two completely different places although they are essentially
> very similar (style attached to each line). I really want to clean
> up this mess for good before moving forward with the separator.
> As above, in the interest of not wasting developer time I'd recommend
> doing the sucky way knowing it is temporary.

It's not wasted time for me; I have already done most of the work (prior
to starting this thread) and it's fun for me. Also I don't think it's
/that/ temporary. I expect it'll take a while until the skin engine can
usefully replace the built-in lists, the progress in this area is rather
slow to put it mildly. I know I could help with it, but I'm sorry it
doesn't catch my interest currently.

> Thinking about it now, it would be pretty cool to register a
> callback (per viewport) for the scroll engine to call which
> would do the line drawing instead of the current code. (It
> would have to be per viewport because it is very likley to
> have a skin scrolling line and the list scrolling line both
> scrolling at the same time, though a generic one would be
> needed for default which should "just work").
> I have the beginnings of a scroll engine rework which does a
> callback (per line, and each line has a viewport associated). But
> even the current scroll engine already stores a viewport pointer
> for each line, that is set when the line is redrawn.
> This I'm interested in seeing. I'm starting to wonder if the scroller
> really needs the viewport pointer per line? If this was changed to
> store just the pixel rectangle to draw in (so the line number is also
> removed, and relative to the screen, not viewport) then it wouldn't
> necessarily overdraw the decorations. The callbacks becomes an issue,
> but I agree that using a callback is the way to go to remove this
> decoration drawing from firmware.

It stores only a viewport pointer currently, so a pixel rectangle is
going to be more expensive from a ram usage POV. The viewport also
provides line selector and font information which is currently needed
(with no callback mechanism).

Best regards.
Received on 2013-03-05

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