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fix(backfill): restore MUI 3.x equality guard, gated on lib_Version #3

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Merged
midwan merged 1 commit into from
May 1, 2026
+17 −0
Merged

fix(backfill): restore MUI 3.x equality guard, gated on lib_Version #3

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17 changes: 17 additions & 0 deletions mcc/Dispatcher.cpp
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Original file line number Diff line number Diff line change
Expand Up @@ -581,6 +581,23 @@ CPPDISPATCHER(_Dispatcher)
b = bmsg->bottom;

if (l>r || t>b) return 0;

/* MUI 3.x (muimaster.library v20 = MUI 3.9, v19 = MUI 3.8) calls
** MUIM_Backfill with bounds that can extend outside the gadget,
** which makes us paint over our siblings ("stuntzi hack").
** MUI 4+ (v21+) calls Backfill correctly with partial regions
** inside the gadget; applying the equality guard there would
** skip every render and produce the blue checkerboard pattern.
*/
if (MUIMasterBase->lib_Version <= 20)
{
if (!(l==_mleft(obj) && t==_mtop(obj) && r==_mright(obj) && b==_mbottom(obj)))
{
D(DBF_ALWAYS, "HTMLview: %ld %ld, %ld %ld, %ld %ld, %ld %ld",
l,_mleft(obj),t,_mtop(obj),r,_mright(obj),b,_mbottom(obj));
return 0;
}
}
}

struct RastPort *rp = _rp(obj);
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