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Minor visible buffer fix for text modes on newer (EGA/VGA) cards

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This commit is contained in:
Jeff Parsons 2015-11-20 10:42:30 -08:00
commit 1dd50c68d3
3 changed files with 5 additions and 3 deletions
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6
modules/pcjs/lib/video.js
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@ -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) {