- VBE banked mode fixes backported from rbench

[dosdemo] / README.md

diff --git a/README.md b/README.md
index ec9721f..7a41535 100644 (file)
--- a/README.md
+++ b/README.md
@@ -1,13 +1,17 @@
-Unnamed Mindlapse DOS demo for Pentium 133
-------------------------------------------
-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 load the `univbe` TSR first.
+Unnamed Mindlapse DOS demo for Pentium-era PCs
+----------------------------------------------
+The demo uses VBE 320x240 16bpp. Some VBE implementations do not expose
+double-scan video modes (240 lines), but can be made to work with a third-party
+VBE TSR like `univbe` or `s3vbe`. Linear framebuffer (VBE 2.0) support is
+recommended, but not necessary. The demo will fallback to VBE 1.2 banked modes
+if LFB modes are not available.
 
 Source structure
 ----------------
  - src/          cross-platform demo framework and miscellaneous utility code
  - src/scr/      demo screens (parts) and effects support code
  - src/dos/      DOS platform code
+ - src/glut/     GLUT platform code (windows/UNIX version)
  - src/sdl/      SDL 1.x platform code (windows/UNIX version)
  - libs/cgmath/  math library, header-file only
  - libs/imago/   image loading library (includes libpng, zlib, libjpeg)
@@ -15,12 +19,6 @@ Source structure
 
 Building on DOS with Watcom
 ---------------------------
-NOTE: Don't. Watcom produces significantly worse code than GCC, and at the
-moment watcom-compiled version of the demo crashes on 3D scenes for some reason
-which I need to investigate at some point. Suspect either inline assembly with
-missing "modify" part, or more likely some FPU optimization which fucks up the
-clipper.
-
 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).
 
@@ -129,3 +127,21 @@ U-only pairable instructions:
  - adc, sbb
  - shr, sar, shl, sal with immediate
  - ror, rol, rcr, rcl with immediate=1
+
+Notes about DJGPP & CWSDPMI
+---------------------------
+Can't use the `hlt` instruction for waiting for interrupts, because we're
+running in ring3 by default. I surrounded all the `hlt` instructions with a
+`USE_HLT` conditional, which is undefined when building with DJGPP.
+
+It's possible to arrange for our code to run on ring0 by changing the DPMI
+provider from `cwsdpmi.exe` to `cwsdpr0.exe` by running:
+`stubedit demo.exe dpmi=cwsdpr0.exe`, but I haven't tested under win9x to see if
+it still works if we do that.
+
+Our fucking segments don't start at 0 ... to access arbitrary parts of physical
+memory we need to call `__djgpp_nearptr_enable()` and use the following macros I
+defined in `cdpmi.h`:
+
+    #define virt_to_phys(v)    ((v) + __djgpp_base_address)
+    #define phys_to_virt(p)    ((p) - __djgpp_base_address)