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Smooth-scroll fix for edge case where scroll offset has returned to zero BUT buffer contents haven't actually been scrolled yet

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This commit is contained in:
Jeff Parsons 2016-08-16 15:40:31 -07:00
commit 12dad7291c
3 changed files with 423 additions and 390 deletions
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39
modules/pc8080/lib/video.js
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@ -157,6 +157,7 @@ function Video(parmsVideo, canvas, context, textarea, container)
if (this.cyCell > 1) {
this.nRowsBuffer++;
this.bScrollOffset = 0;
this.fSkipSingleCellUpdate = false;
}
/*
@ -778,7 +779,26 @@ Video.prototype.updateScrollOffset = function(bScroll)
this.printMessage("updateScrollOffset(" + bScroll + ")");
if (this.bScrollOffset !== bScroll) {
this.bScrollOffset = bScroll;
this.updateScreen(-1);
/*
* WARNING: If we immediately redraw the screen on the first wrap of the scroll offset back to zero,
* we end up "slamming" the screen's contents back down again, because it seems that the frame buffer
* contents haven't actually been scrolled yet. So we redraw now ONLY if bScroll is non-zero, lest
* we ruin the smooth-scroll effect.
*
* And this change, while necessary, is not sufficient, because another intervening updateScreen()
* call could still occur before the frame buffer contents are actually scrolled; and ordinarily, if the
* buffer hasn't changed, updateScreen() would do nothing, but alas, if the cursor happens to get toggled
* in the interim, updateScreen() will want to update exactly ONE cell.
*
* So we deal with that by setting the fSkipSingleCellUpdate flag. Now of course, there's no guarantee
* that the next update of only ONE cell will always be a cursor update, but even if it isn't, skipping
* that update doesn't seem like a huge cause for concern.
*/
if (bScroll) {
this.updateScreen(-1);
} else {
this.fSkipSingleCellUpdate = true;
}
}
};
@ -1043,9 +1063,10 @@ Video.prototype.updateVT100 = function(fForced)
var nRows = 0;
var nFill = (this.rateMonitor == 60? 2 : 5);
var iCell = 0, cUpdated = 0, iCellUpdated = -1;
this.assert(this.abLineBuffer.length == this.nColsBuffer);
var iCell = 0, cUpdated = 0;
while (nRows < this.nRowsBuffer) {
/*
* Populate the line buffer
@ -1101,7 +1122,7 @@ Video.prototype.updateVT100 = function(fForced)
for (var iCol = 0; iCol < nCols; iCol++) {
data = this.abLineBuffer[iCol];
if (!fLineCacheValid || data !== this.aCellCache[iCell]) {
this.aCellCache[iCell] = data;
this.aCellCache[iCellUpdated = iCell] = data;
this.updateChar(font, iCol, nRows, data, this.contextBuffer);
cUpdated++;
}
@ -1125,6 +1146,18 @@ Video.prototype.updateVT100 = function(fForced)
this.printMessage("updateVT100(): update #" + this.nUpdateNumber + " at " +this.nUpdateSeconds + " corner=" + str.toHexByte(this.aCellCache[1]) + " cycles=" + this.nCyclesPrev + " delta=" + this.nCyclesDelta);
}
if (!fForced && this.fSkipSingleCellUpdate && cUpdated == 1) {
/*
* We're going to blow off this update, since it comes on the heels of a smooth-scroll that *may*
* not be completely finished yet, and at the same time, we're going to zap the only updated cell
* cache entry, to guarantee that it's redrawn on the next update.
*/
this.assert(iCellUpdated >= 0);
this.aCellCache[iCellUpdated] = -1;
cUpdated = 0;
}
this.fSkipSingleCellUpdate = false;
if ((cUpdated || fForced) && this.contextBuffer) {
/*
* We must subtract cyCell from cyBuffer to avoid displaying the extra "scroll line" that we normally