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Fix: prevent LED flash on cold boot when a boot preset is configured #5676

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leuenbert wants to merge 2 commits into from
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Fix: prevent LED flash on cold boot when a boot preset is configured #5676

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adb2f28
feat: prevent flickering
leuenbert Jun 10, 2026
fa1317e
Merge branch 'wled:main' into main
leuenbert Jun 10, 2026
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35 changes: 25 additions & 10 deletions wled00/wled.cpp
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Original file line number Diff line number Diff line change
Expand Up @@ -507,6 +507,7 @@ void WLED::setup()
handlePresets(); // handle boot preset
handlePlaylist(); // handle playlist if preset queued one
handlePresets(); // handle presets again to give a chance for anything queued by the boot preset or playlist
strip.setTransition(transitionDelayDefault); // restore transitions now that the boot preset applied instantly (no boot flash)
}

if (strcmp(multiWiFi[0].clientSSID, DEFAULT_CLIENT_SSID) == 0 && !configBackupExists())
Expand Down Expand Up @@ -617,19 +618,28 @@ void WLED::beginStrip()
offMode = false; // init to on state to allow proper relay init
handleOnOff(true); // init relay and force off

if (turnOnAtBoot) {
// fix for #3196 and the boot flash: if a boot preset is configured, fully blank the strip and
// push a black frame before applying it. The boot preset is applied with a transition, which
// crossfades FROM the current (restored) segment buffer; without a black starting frame that
// restored state flashes at the restored brightness for the first fraction of a second.
// This must run for turnOnAtBoot too. Brightness 0 alone (the boot brightness still feeds the
// crossfade's source) and blanking colors[0] alone (palette/FX states still render) are each
// insufficient on their own, which is why earlier attempts still flashed.
if (bootPreset > 0) {
// set all segments black (no transition)
for (unsigned i = 0; i < strip.getSegmentsNum(); i++) {
Segment &seg = strip.getSegment(i);
if (seg.isActive()) seg.colors[0] = BLACK;
}
colPri[0] = colPri[1] = colPri[2] = colPri[3] = 0; // needed for colorUpdated()
briLast = briS; bri = 0; // stay dark; the boot preset sets its own brightness when it applies
strip.fill(BLACK);
if (rlyPin < 0)
strip.show(); // push a black frame so the boot preset's transition starts from black
} else if (turnOnAtBoot) {
if (briS > 0) bri = briS;
else if (bri == 0) bri = 128;
} else {
// fix for #3196
if (bootPreset > 0) {
// set all segments black (no transition)
for (unsigned i = 0; i < strip.getSegmentsNum(); i++) {
Segment &seg = strip.getSegment(i);
if (seg.isActive()) seg.colors[0] = BLACK;
}
colPri[0] = colPri[1] = colPri[2] = colPri[3] = 0; // needed for colorUpdated()
}
briLast = briS; bri = 0;
strip.fill(BLACK);
if (rlyPin < 0)
Expand All @@ -638,6 +648,11 @@ void WLED::beginStrip()
colorUpdated(CALL_MODE_INIT); // will not send notification but will initiate transition
if (bootPreset > 0) {
applyPreset(bootPreset, CALL_MODE_INIT);
// keep transitions disabled until the boot preset has actually been applied (in setup(), after
// beginStrip() returns) so it applies instantly with NO crossfade from the restored state -
// a crossfade is what makes the restored state flash on cold boot. Transitions are restored
// in setup() right after the boot preset/playlist is handled.
return;
}

strip.setTransition(transitionDelayDefault); // restore transitions
Expand Down
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