From 1dd50c68d3571e3e4a2c1450d501ab60ed7015bc Mon Sep 17 00:00:00 2001
From: Jeff Parsons <Jeff@pcjs.org>
Date: Fri, 20 Nov 2015 10:42:30 -0800
Subject: [PATCH] Minor visible buffer fix for text modes on newer (EGA/VGA)
 cards

---
 disks/pc/dos/microsoft/4.00/machine.xml | 1 -
 disks/pc/dos/microsoft/4.01/machine.xml | 1 -
 modules/pcjs/lib/video.js               | 6 +++++-
 3 files changed, 5 insertions(+), 3 deletions(-)

diff --git a/disks/pc/dos/microsoft/4.00/machine.xml b/disks/pc/dos/microsoft/4.00/machine.xml
index 9d3a1d12d..025429c56 100644
--- a/disks/pc/dos/microsoft/4.00/machine.xml
+++ b/disks/pc/dos/microsoft/4.00/machine.xml
@@ -9,7 +9,6 @@
 	<rom id="romBIOS" addr="0xf0000" size="0x10000" alias="0xff0000" file="/devices/pc/bios/5170/1984-01-10.json"/>
 	<video ref="/devices/pc/video/ibm/ega/ibm-ega-128kb-autolockfs.xml"/>
 	<keyboard ref="/devices/pc/keyboard/keyboard-minimal.xml"/>
-	<panel ref="/devices/pc/panel/wide.xml"/>
 	<fdc ref="/disks/pc/library.xml" pos="right" automount='{A: {name: "MS-DOS 4.00 (Disk 1)", path: "/disks/pc/dos/microsoft/4.00/MSDOS400-DISK1.json"}}'/>
 	<chipset id="chipset" model="5170" floppies="[1200,1200]"/>
 	<serial id="com1" adapter="1"/>
diff --git a/disks/pc/dos/microsoft/4.01/machine.xml b/disks/pc/dos/microsoft/4.01/machine.xml
index 843e5e3f6..203ff6d33 100644
--- a/disks/pc/dos/microsoft/4.01/machine.xml
+++ b/disks/pc/dos/microsoft/4.01/machine.xml
@@ -9,7 +9,6 @@
 	<rom id="romBIOS" addr="0xf0000" size="0x10000" alias="0xff0000" file="/devices/pc/bios/5170/1984-01-10.json"/>
 	<video ref="/devices/pc/video/ibm/ega/ibm-ega-128kb-autolockfs.xml"/>
 	<keyboard ref="/devices/pc/keyboard/keyboard-minimal.xml"/>
-	<panel ref="/devices/pc/panel/wide.xml"/>
 	<fdc ref="/disks/pc/library.xml" pos="right" automount='{A: {name: "MS-DOS 4.01 (Disk 1)", path: "/disks/pc/dos/microsoft/4.01/MSDOS401-DISK1.json"}}'/>
 	<chipset id="chipset" model="5170" floppies="[1200,1200]"/>
 	<serial id="com1" adapter="1"/>
diff --git a/modules/pcjs/lib/video.js b/modules/pcjs/lib/video.js
index da20600a2..00b627a34 100644
--- a/modules/pcjs/lib/video.js
+++ b/modules/pcjs/lib/video.js
@@ -5406,10 +5406,14 @@ Video.prototype.updateScreen = function(fForce)
          * cbScreen was computed (but without any CGA-related padding considerations).
          *
          * TODO: I'm taking a lot of shortcuts in this calculation (eg, relying on nFont to detect text modes,
-         * ignoring MODE_CTRL.BYTE_MODE, etc); generalize this someday.
+         * ignoring MODE_CTRL.BYTE_MODE, etc); generalize this someday.  In addition, dividing the total number of
+         * cells by nCellsPerWord yields total WORDS, not BYTES, so we need to double cbScreen -- EXCEPT that the
+         * notion of cell has a slightly different meaning for EGA and VGA-specific modes.  nCellsPerWord should
+         * not be overloaded like that.
          */
         this.nColsLogical = card.regCRTData[Card.CRTC.EGA.OFFSET] << (this.nFont? 1 : (card.regCRTData[Card.CRTC.EGA.UNDERLINE.INDX] & Card.CRTC.EGA.UNDERLINE.DWORD)? 3 : 4);
         cbScreen = ((this.nColsLogical * (this.nRows-1) + this.nCols) / this.nCellsPerWord)|0;
+        if (this.nMode <= Video.MODE.MDA_80X25) cbScreen <<= 1;
     }
 
     if (addrScreen + cbScreen > addrScreenLimit) {