If the X server is not shut down cleanly, it may leave lock files
around that "vncserver" has previously mis-identified as evidence that
the display number is still in use.

Instead of checking for existence of /tmp/.X<n>-lock, the code will
now extract the PID from the lock file and confirm that a process
exists with the same PID. This will eliminate false positives in the
case that this file references a PID that no longer exists. The Xorg
server does not have a problem with fixing this file when it next
starts up. It is only important to avoid using the port if it is still
in use.

The display check had duplicate code to first check if the X11 port is
not in use, and then check that the RFB port is not in use. Eliminate
the duplicate code by using a for-loop.

Several calculated values such as file paths and port numbers were
hard coded within strings or expressions, sometimes multiple
times. These values should be extracted into named variables to
improve self-documentation and avoid accidental divergence.

Checking for the existence of `/tmp/.X<n>-lock` is a fast read-only
operation, while calls to bind() or connect() are more expensive and
may have side effects. Perform the fast operation first.

The check for existence of `/usr/spool/sockets/X11/<n>` has been
removed. This file is only relevant on HP-UX, and TigerVNC dropped
support for HP-UX in commit 31e5aa3.

Add missing build requirements: libpng-devel, zlib-devel

Remove obsolete build requirements: libXfont-devel

Fix unexpected rpm macro expansion `%{VERSION}` which is supposed
to be passed through as literal to `rpm -q --qf`. This hasn't
caused problems before, but it was found to cause problems when
built from EL 8 when it expanded to "1.10.1".

64x64 changed block can be large for fine changes such as cursor
movement and typing in terminal windows, or an update to a clock.

If the block can be efficiently cropped, this will reduce latency
and bandwidth. Every pixel cropped is a pixel less to analyze, encode,
transmit, and decode.

The previous code already detected the top of the change in order
to determine if the block had changed. However, it did not use
this information to reduce the size of the change rectangle, nor
did it calculate any of the other edges.

The new code introduces detection of the other edges, and uses
the information to build a reduced area change rectangle. This
has the additional effect of reducing the number of discrete pixel
values in the change block which may allow a more efficient
encoding algorithm to be selected.

As this section of code is performance sensitive, the method
of detecting the edges has been optimized to quickly fall back
to pessimistic values as soon as a single comparison fails on
each edge. In the case that full 64x64 block are changing,
there will be three extra comparisons per block.

In cases where the change rectangle can be reduced from 64x64,
the reduced size of the change rectangle represents reduced
effort to encode, transfer, and decode the contained pixels.

In the case of images with high frequency changes, which
specifically includes text, the lossy JPEG encoding can be
highly distorted, especially with JPEG level 6 or less. The
quick flash from a distorted JPEG to a lossless JPEG can
appear as a flickering to some people. This effect was more
obvious when the surrounding area is not expected to change,
but is being distorted anyways due to being part of the 64x64
blocking algorithm.

In the case of a user typing in a terminal window, this change
may commonly reduce the number of pixels updated with every
character typed from 4096 pixels (64x64) to 640 pixels (32x20)
or less.

It doesn't work very well so it shouldn't be included by default.

It uses bash-isms so a POSIX shell will not work correctly.

It's just confusing when this is split over two directories.

Don't just build things, also test the various packaging.

If using SSecurityPlain and the user specifies an empty username
and password, it will invoke InStream::checkNoWait(0) which will
cause a division by zero when calculating the number of available
items.

Enhance InStream::check() to behave properly when asked for
zero items, or zero sized items.

Add comments to InStream::check(), InStream::checkNoWait(),
and InStream::readBytes() to document expected behaviour
when requested to check or read zero items, or an item with
zero size.

It's quite easy to make a mistake and add an additional space when configuring
users in the vncserver.users config file. You will then get an error that the
user doesn't exist and it's hard to spot the mistake. Same applies for a space
before the display number.

A "0x" prefix suggest hexadecimal values, not decimal.

Since 8e09912 this wasn't triggered properly as we checked if all
clients were gone before we actually removed the last client from our
list.

If the difference in angle is larger than 180 degrees we hit a corner
case. This commit modifies the coordinates of an existing test to cover
this.

Makes it easier to understand what the tests do.

Update RPM package build process to automatically detect and apply
the correct X.org patch.

It allows us to use the more standard format specifiers.

This is fine for simple structs but not class based objects.

We still target a very old version of macOS, which tends to make clang
very upset, so we need to turn off depercation warnings.

Some compilers get upset if a declaration comes after the definition.

The method it overloads got tweaked some time ago, so we need to make
sure this method follows suit.

Sends response for SetDesktopSize as per the community wiki
specification

This adds the same touch gesture support for Windows as already added
for Unix. Note that it uses Windows gesture detection instead of our own
here though to give the user a familiar experience. Unfortunately that
means we lose the three finger tap.

This also raises the base requirements to Windows 7 as that's when
Windows got proper touch support.

Allows the user to perform certain important mouse operations using
touch gestures instead.

We have a timer after Ctrl is pressed in order to see if an Alt will
come right after. Ctrl + Alt is what windows sends for AltGr.
If a key other than Alt was pressed we knew that we could cancel this
timer, this commit extends that to mouse events too.

Since this detection breaks the true order of events we want to make
a decision as fast as possible.

Switch from using Core events to using X Input events for pointer
devices in order to differentiate between mouse events and touch events.

Because FLTK doesn't understand X Input 2, we intercept these events and
translate them to core events where possible.

If you have the setting "Emulate middle mouse button" turned on, a click
and drag can fail if it is done very quickly. The position of the
initial click will be incorrect in such a case because the timeout will
delay events.

We need to make sure everything happens in the correct order during
startup for the X11 display to open correctly. Primarily it means
we need to parse the arguments and open the display before anything
might make any X11 calls, as we may have a -display argument.