A recent update has broken csgo so it's not updating the screen. It seems that it is a change to X11 though and not a Steam or CS:GO update. The screen only refreshes as long as you are moving your mouse or pressing a key which makes it very hard to play. I have this problem on Slackware64-current but I guess it also affects 32 bit Slackware too (if CS:GO even still works on 32 bit Linux).
The thing that broke it is a change in libX11 version 1.8.3, but on Slackware there was no easy way to go back to 1.8.2 so I had to recompile 1.8.3 but with the patch removed which broke things.
The patch can be downloaded from https://github.com/archlinux/svntogit-packages/blob/packages/libx11/trunk/0001-Revert_Update_XPutBackEvent.diff and the source code from http://ftp.slackware.com/pub/slackware/slackware64-current/source/x/x11/src/lib/libX11-1.8.3.tar.xz.

You can make a temporary package with the patch reverted by doing (at your own risk)

# tar xvf libX11-1.8.3.tar.xz
# cd libX11-1.8.3
# patch -p1 < ../0001-Revert_Update_XPutBackEvent.diff 
# ./configure --prefix=/usr --libdir=/usr/lib64
# make
# make install DESTDIR=/tmp/pkg-libx11
# cd /tmp/pkg-libx11
# makepkg -l y -c y /tmp/libX11-1.8.3-x86_64-2.txz
# upgradepkg --reinstall /tmp/libX11-1.8.3-x86_64-2.txz

When a new official libX11 is released it will replace this temporary one, and hopefully include the patch to fix cs:go :)

edit: I added the libdir flag to configure which makes more sense than editing files after to update it.