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bugfix to prevent "infinite" loop in palette blend #4841

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DedeHai merged 1 commit into from
Aug 28, 2025
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bugfix to prevent "infinite" loop in palette blend #4841

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2 changes: 2 additions & 0 deletions wled00/FX_fcn.cpp
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Original file line number Diff line number Diff line change
Expand Up @@ -282,6 +282,7 @@ void Segment::startTransition(uint16_t dur, bool segmentCopy) {
_t->_oldSegment = new(std::nothrow) Segment(*this); // store/copy current segment settings
_t->_start = millis(); // restart countdown
_t->_dur = dur;
_t->_prevPaletteBlends = 0;
if (_t->_oldSegment) {
_t->_oldSegment->palette = _t->_palette; // restore original palette and colors (from start of transition)
for (unsigned i = 0; i < NUM_COLORS; i++) _t->_oldSegment->colors[i] = _t->_colors[i];
Expand Down Expand Up @@ -368,6 +369,7 @@ void Segment::beginDraw(uint16_t prog) {
// minimum blend time is 100ms maximum is 65535ms
#ifndef WLED_SAVE_RAM
unsigned noOfBlends = ((255U * prog) / 0xFFFFU) - _t->_prevPaletteBlends;
if(noOfBlends > 255) noOfBlends = 255; // safety check
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@blazoncek blazoncek Aug 16, 2025

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No need for this check.

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@DedeHai DedeHai Aug 16, 2025

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are you 100% sure there are no possible combinations where transition time changes i.e. prog gets smaller and _prevPaletteBlends is not reset?

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@blazoncek blazoncek Aug 16, 2025

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If we trust in math then yes.
I.e. prog is a _t->_progress alias. _progress only increases with time. One exception is the one you found, when transition is restarted (_start and _dur change) to create a segment copy.

for (unsigned i = 0; i < noOfBlends; i++, _t->_prevPaletteBlends++) nblendPaletteTowardPalette(_t->_palT, Segment::_currentPalette, 48);
Segment::_currentPalette = _t->_palT; // copy transitioning/temporary palette
#else
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