Reworking sixel implementation based on veltza's implementation (#117)

* sixel: remove black bars from sixel images

When the images don't fully cover the text cells, black bars are added
to them. This fix removes those bars, but if you need the old behavior,
you can restore it by setting 'sixelremovebars' to zero in config.h

* sixel: fix a potential memory leak

* sixel: improve behavior with text reflow

* sixel: prevent animated gifs from choking the terminal

Animated gifs constantly spawn new images that eventually choke the
terminal because the old animation frames are kept in the image buffer.
This fix removes overlapping images from the image buffer and prevents
them from piling up.

* sixel: add zooming and clipping

* sixel: copying bulk of changes

* sixel: move sixel_parser_parse() and add missing sequences and blocks (#113)

- Move sixel_parser_parse() from tputc() to twrite()
- Add missing 8452, DECSDM, XTSMGRAPHICS and XTWINOPS sequences
- Add more conditional blocks for the scrollback and sync patches
- Remove unused reflow_y from ImageList. It is only used for the
  scrollback-reflow patch in st-sx.

* sixel: update vtiden to VT200 family

* sixel: fix scrolling issues inside tmux (#114)

tmux is using the scrolling region and sequence to clear the screen
below the shell prompt. This peculiar behavior caused the tscrollup()
function to be called, which always scrolled the images regardless of
whether they were inside the region or not. So the images moved out of
place whenever the bottom of the screen was cleared. This fix checks
that the images are inside the region before scrolling them.

* sixel: prevent images from being deleted when resizing (#115)

This fixes resizing issues outside of tmux not inside.

* Rewriting tresize logic based on veltza's proposed implementation in PR #115

* tresize: correction for tscrollup call when scrollback patch is used

---------

Co-authored-by: veltza <106755522+veltza@users.noreply.github.com>

config.mk

@@ -13,10 +13,10 @@ X11LIB = /usr/X11R6/lib
 PKG_CONFIG = pkg-config
 
 # Uncomment this for the alpha patch / ALPHA_PATCH
-#XRENDER = -lXrender
+#XRENDER = `$(PKG_CONFIG) --libs xrender`
 
 # Uncomment this for the themed cursor patch / THEMED_CURSOR_PATCH
-#XCURSOR = -lXcursor
+#XCURSOR = `$(PKG_CONFIG) --libs xcursor`
 
 # Uncomment the lines below for the ligatures patch / LIGATURES_PATCH
 #LIGATURES_C = hb.c
@@ -26,13 +26,14 @@ PKG_CONFIG = pkg-config
 
 # Uncomment this for the SIXEL patch / SIXEL_PATCH
 #SIXEL_C = sixel.c sixel_hls.c
+#SIXEL_LIBS = `$(PKG_CONFIG) --libs imlib2`
 
 # includes and libs, uncomment harfbuzz for the ligatures patch
 INCS = -I$(X11INC) \
        `$(PKG_CONFIG) --cflags fontconfig` \
        `$(PKG_CONFIG) --cflags freetype2` \
        $(LIGATURES_INC)
-LIBS = -L$(X11LIB) -lm -lrt -lX11 -lutil -lXft ${XRENDER} ${XCURSOR}\
+LIBS = -L$(X11LIB) -lm -lrt -lX11 -lutil -lXft ${SIXEL_LIBS} ${XRENDER} ${XCURSOR}\
        `$(PKG_CONFIG) --libs fontconfig` \
        `$(PKG_CONFIG) --libs freetype2` \
        $(LIGATURES_LIBS)