FBSCALE in SDL backend

[dosdemo] / README.md

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+Building and running on DOS
+---------------------------
+Make sure you have Watcom or OpenWatcom installed, and the appropriate env-vars
+set (the watcom installer automatically adds them to autoexec.bat by default).
+
+Run wmake to build. Needs dos4gw.exe in current dir.
+
+The demo requires VESA Bios Extensions (VBE) 2.0. If your graphics card doesn't
+support VBE 2.0 or greater, then make sure to run the `univbe` TSR first, or
+the demo will fail to find a usable LFB video mode.
+
+
+Cross-compile on GNU/Linux
+--------------------------
+source owdev script with contents (change WATCOM var as necessary):
+
+  export WATCOM=$HOME/devel/ow
+  export PATH=$WATCOM/binl:$PATH
+  export INCLUDE=$WATCOM/h:$INCLUDE
+
+Run wmake to build. Needs dos4gw.exe and wstub.exe in current dir or PATH
+
+Simply running ./demo.exe might invoke magic of the ancients to start wine,
+which will in turn start dosbox, which will execute the DOS binary! If the gods
+are slumbering in valhalla, just typing `dosbox demo.exe` should do the trick.
+
+
+SDL backend
+-----------
+Run make to build (assuming make on your system is GNU make).
+
+The SDL backend will scale the framebuffer up, by the factor specified in the
+`FBSCALE` environment variable. So run the demo as: `FBSCALE=3 ./demo` for
+a 3x scale factor, or just export the `FBSCALE` env var in the shell you are
+going to use for running the demo. The default scale factor is 2x.