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SCUMM: (FM-Towns) - improve smooth scroling

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I have made the scrolling more smooth and still hopefully managed not to break the sync with the engine (which really is a bit tricky).
I've tested playing the ZAK and LOOM intros and also walking around in ZAK and MI2, since there are some good test cases there. I've also compared all these side by side with the UNZ emulator.
This commit is contained in:
athrxx 2021-05-16 18:01:19 +02:00
parent 82959d4ce8
commit fb8f108402
2 changed files with 12 additions and 5 deletions
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4
engines/scumm/gfx_towns.cpp
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@ -186,13 +186,13 @@ void ScummEngine::towns_updateGfx() {
return;
uint32 cur = _system->getMillis();
while (_scrollTimer <= cur) {
if (_scrollTimer <= cur) {
if (!_scrollTimer)
_scrollTimer = cur;
_scrollTimer += 1000 / 60;
_townsScreen->scrollLayers(1, _scrollRequest);
if (_townsScreen->isScrolling(0))
_scrollDeltaAdjust = 1;
_scrollDeltaAdjust++;
_scrollRequest = 0;
}

13
engines/scumm/scumm.cpp
View File

@ -2275,9 +2275,16 @@ Common::Error ScummEngine::go() {
// Determine how long to wait before the next loop iteration should start
int delta = (VAR_TIMER_NEXT != 0xFF) ? VAR(VAR_TIMER_NEXT) : 4;
#ifndef DISABLE_TOWNS_DUAL_LAYER_MODE
// FM-Towns only. The original does this to make the engine wait for the scrolling to catch up.
if (_scrollDeltaAdjust)
delta = delta * 4 / (4 - _scrollDeltaAdjust);
// FM-Towns only. The original has a mechanism to let the scrolling catch up to the engine. This avoids glitches, e. g.
// when the engine draws actors or objects to the far left/right of the screen while the scrolling hasn't caught up yet.
// MI2 FM-Towns normally adds an amount of 4 to a counter on each 60 Hz tick from inside an interrupt handler, but only
// an amount of 3 while the smooth scrolling is in progress. The counter divided by 4 has to reach the VAR_TIMER_NEXT
// before the main loop continues. We try to imitate that behaviour here to avoid glitches, but without making it
// overly complicated...
if (_scrollDeltaAdjust) {
int adj = MIN<int>(_scrollDeltaAdjust * 4 / 3 - _scrollDeltaAdjust, delta * 4 / 3 - delta);
delta += adj;
}
_scrollDeltaAdjust = 0;
#endif
if (delta < 1) // Ensure we don't get into an endless loop