I have another patch here for review that optimizes the performance of
glyph drawing, primarily when using non-unit kerning values, and fixes a
few other minor issues. It's dependent on the earlier patch from me that
stores unicode codepoints in a Rune type, typedef'd to uint_least32_t.

This patch is a pretty big change to xdraws so your scrutiny is
appreciated.

First, some performance numbers. I used Yu-Jie Lin termfps.sh shell
script to benchmark before and after, and you can find it in the
attachments. On my Kaveri A10 7850k machine, I get the following
results:

Before Patch
============

1) Font: "Liberation Mono:pixelsize=12:antialias=false:autohint=false"
   cwscale: 1.0, chscale: 1.0
   For 273x83 100 frames.
   Elapsed time :     1.553
   Frames/second:    64.352
   Chars /second: 1,458,159

2) Font: "Inconsolata:pixelsize=14:antialias=true:autohint=true"
   cwscale: 1.001, chscale: 1.001
   For 239x73 100 frames.
   Elapsed time :   159.286
   Frames/second:     0.627
   Chars /second:    10,953

After Patch
===========

3) Font: "Liberation Mono:pixelsize=12:antialias=false:autohint=false"
   cwscale: 1.0, chscale: 1.0
   For 273x83 100 frames.
   Elapsed time :     1.544
   Frames/second:    64.728
   Chars /second: 1,466,690

4) Font: "Inconsolata:pixelsize=14:antialias=true:autohint=true"
   cwscale: 1.001, chscale: 1.001
   For 239x73 100 frames.
   Elapsed time :     1.955
   Frames/second:    51.146
   Chars /second:   892,361

As you can see, while the improvements for fonts with unit-kerning is
marginal, there's a huge ~81x performance increase with the patch when
using kerning values other than 1.0.

So what does the patch do?

The `xdraws' function would render each glyph one at a time if non-unit
kerning values were configured, and this was the primary cause of the
slow down. Xft provides a handful of functions which allow you to render
multiple characters or glyphs at time, each with a unique <x,y> position,
so it was simply a matter of massaging the data into a format that would
allow us to use one of these functions.

I've split `xdraws' up into two functions. In the first pass with
`xmakeglyphfontspecs' it will iterate over all of the glyphs in a given
row and it will build up an array of corresponding XftGlyphFontSpec
records. Much of the old logic for resolving fonts for glyphs using Xft
and fontconfig went into this function.

The second pass is done with `xrenderglyphfontspecs' which contains the
old logic for determining colors, clearing the background, and finally
rendering the array of XftGlyphFontSpec records.

There's a couple of other things that have been improved by this patch.
For instance, the UTF-32 codepoints in the Line's were being re-encoded
back into UTF-8 strings to be passed to `xdraws' which in turn would then
decode back to UTF-32 to verify that the Font contained a matching glyph
for the code point. Next, the UTF-8 string was being passed to
`XftDrawStringUtf8' which internally mallocs a scratch buffer and decodes
back to UTF-32 and does the lookup of the glyphs all over again.

This patch gets rid of all of this redundant round-trip encoding and
decoding of characters to be rendered and only looks up the glyph index
once (per font) during the font resolution phase. So this is probably
what's responsible for the marginal improvements seen when kerning values
are kept to 1.0.

I imagine there are other performance improvements here too, not seen in
the above benchmarks, if the user has lots of non-ASCII code plane characters
on the screen, or several different fonts are being utilized during
screen redraw.

Anyway, if you see any problems, please let me know and I can fix them.

When user clicks LMB, one character is selected, but will not be copied
to selection until the user moves cursor a bit. Therefore, the character
should not be highlighted as selected yet.

Before the patch, the trick was not to mark line as dirty to avoid
highlighting it. However, if user has already selected something and
clicks in line that contains selection, selclear sets the line as dirty
and one character is highlighted when it should not.

This patch replaces dirty trick with explicit check for sel.mode inside
selected().

This patch also prevents sel.mode from increasing beyond 2. It is almost
impossible, but sel.mode may overflow if mouse is moved around for too
long while selecting.

Special case is when regular selection spans multiple lines.
Otherwise, just sort sel.ob.x and sel.ob.y.

Also make sure y never exceeds term.row-1 even if ATTR_WRAP is set for
some reason.

Only wait for termination of the shell.

Signed-off-by: Daniel Martí <mvdan@mvdan.cc>

Signed-off-by: Daniel Martí <mvdan@mvdan.cc>

Signed-off-by: Daniel Martí <mvdan@mvdan.cc>

This parameter was always UTF_SIZ, so it is better remove it and
use directly UTF_SIZ in it.

st.c:1321:2: warning: ignoring return value of function declared with warn_unused_result attribute [-Wunused-result]
            system(cmd);
            ^~~~~~ ~~~

Debatable whether an error here should case exit(EXIT_FAILURE). Just
preserving the existing behaviour for now.

We cannot pass strescseq.args[0] to atoi when nargs is zero,
because in this case it will be null.

LEN(colorname) may be below 256 for some configurations.

WIN_REDRAW flag was not used since introduction of Xdbe
in commit 94771d0588

This way is a bit more accurate.

The check was introduced back when st used gettimeofday.
The condition is also modified to increment the accuaracy of the
calculation.

Not always is desirable to create a pseudo terminal, and some times
we want to open a terminal emulator over a tty line. With this new
patch is possible to do someting like:

	$ st -l /dev/ttyS0 115200

Without this option was needed to launch another terminal emulator
over st (for example minicom, picocom, cu, ...).

This fixes a segmentation fault on some systems.

This change allows execute st as 'st mutt' while it keeps the
compability with xterm and urxt.

ICCCM mandates the use of real timestamps to interact with the
selection, to rule out race conditions if the clients are run at
different speeds. I have implemented the low hanging fruit, putting the
timestamps into text selection. Also, ICCCM mandates a check for whether
XSetSelectionOwner() worked. Not sure my version is correct, though.

tmoveto resets CURSOR_WRAPNEXT.

Simple testcase:

for i in $(seq 1 200); do
	printf '\t.';
	usleep 100000;
	printf '\t@';
	usleep 100000;
done

In st executing this script causes @ and . to overwrite each other in
the last column.

It probably refers to
http://lists.suckless.org/dev/1211/13427.html
and does not seem like a bug in st.

We do not free it until exit anyway.

LIMIT returns value. This fact is already used in x2col and y2row.

It seems that LICENSE files are more common than LICENCE files.
At least this patch makes spelling consistent.

There is no need to check that slide > 0 before executing loop.
If slide <= 0, loop stops immediately.

XFilterEvent usually filters KeyPress events according to input method.
At this point the window is not mapped. The only events that we process
are ConfigureNotify and MapNotify. They should not be filtered by input
method.