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Move non-CPU-related update functions to the Computer component

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This commit is contained in:
Jeff Parsons 2016-03-30 17:04:36 -07:00
commit e02706ab08
18 changed files with 2557 additions and 2553 deletions
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32
modules/pcjs/lib/video.js
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@ -5758,28 +5758,20 @@ Video.prototype.updateScreenGraphicsEGA = function(addrBuffer, addrScreen, addrS
if (x < xDirty) xDirty = x;
for (iPixel = 0; iPixel < nPixels; iPixel++) {
/*
* We must follow the golden JavaScript rule of appending "|0" to all hex constants with bit 31 set.
* The innocuous use of the bit-wise OR operator has the side-effect of producing a negative value,
* matching how entries in Video.aEGADWToByte are initialized (eg, "Video.aEGADWToByte[0x80000000|0]").
*/
var dwPixel = data & (0x80808080|0);
/*
* This was the old approach to dealing with negative hex values, by converting them to positive
* values that didn't alter the low 32 bits. But it's not ideal, because it requires using values here
* and in the array that are outside the signed 32-bit range, potentially triggering floating-point.
*
* if (dwPixel < 0) dwPixel += 0x100000000;
*
* An even simpler solution would be to use the unsigned right-shift operator:
*
* dwPixel >>> 0
*
* but again, all that does is produce a value outside the signed 32-bit range, which is sub-optimal.
* 0x80808080 may LOOK like a 32-bit value, but it is not, because JavaScript treats it as a POSITIVE
* number, and therefore outside the normal 32-bit integer range; however, the AND operator guarantees
* that the result will be a 32-bit value, so it doesn't matter.
*/
var dwPixel = data & 0x80808080;
this.assert(Video.aEGADWToByte[dwPixel] !== undefined);
/*
* Since assertions don't fix problems (only catch them, and only in DEBUG builds), I'm also ensuring
* that bPixel will always default to 0 if an undefined value ever slips through again.
* that bPixel will default to 0 if an undefined value ever slips through again.
*
* How did an undefined value slip through? We had (incorrectly) initialized entries in aEGADWToByte;
* for example, we used to set aEGADWToByte[0x80808080] instead of aEGADWToByte[0x80808080|0]. The
* former is a POSITIVE index that is outside the 32-bit integer range, whereas the latter is a NEGATIVE
* index, which is what this code requires.
*/
var bPixel = Video.aEGADWToByte[dwPixel] || 0;
this.setPixel(this.imageScreenBuffer, x++, y, aPixelColors[bPixel]);
@ -5923,8 +5915,8 @@ Video.prototype.getRetraceBits = function(card)
/*
* NOTE: The CGA bits CGA.STATUS.RETRACE (0x01) and CGA.STATUS.VRETRACE (0x08) match the EGA definitions,
* and they also correspond to the MDA bits MDA.STATUS.HDRIVE (0x01) and MDA.STATUS.BWVIDEO (0x08); I'm not sure why
* the MDA uses different designations, but the bits appear to serve the same purpose.
* and they also correspond to the MDA bits MDA.STATUS.HDRIVE (0x01) and MDA.STATUS.BWVIDEO (0x08); I'm not sure
* why the MDA uses different designations, but the bits appear to serve the same purpose.
*
* TODO: Decide whether this more faithful emulation of the retrace bits should be extended to the MDA/CGA, too;
* doing so might slow down the BIOS scroll code a bit, though.