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lottie: fix offsetting partially degenerated cubics

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Until now, cases where a Bezier curve had `start == ctrl1` or
`ctrl2 == end` were incorrectly treated as linear segments.
This led to incorrect rendering, for example when offsetting
a polystar with outer roundness > 0 and inner roundness == 0.
Now such cases handled as proper curves with full cubic behavior.
This commit is contained in:
Mira Grudzinska 2025-06-11 23:26:14 +02:00
parent 50b001f018
commit 85885575b5
1 changed files with 30 additions and 13 deletions
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43
src/loaders/lottie/tvgLottieModifier.cpp
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@ -330,6 +330,10 @@ bool LottieOffsetModifier::modifyPath(PathCommand* inCmds, uint32_t inCmdsCnt, P
auto offset = _clockwise(inPts, inPtsCnt) ? this->offset : -this->offset;
auto threshold = 1.0f / fabsf(offset) + 1.0f;
bool inside{};
Point intersect{};
bool degeneratedLine1{}, degeneratedLine3{};
for (uint32_t iCmd = 0, iPt = 0; iCmd < inCmdsCnt; ++iCmd) {
if (inCmds[iCmd] == PathCommand::MoveTo) {
state.moveto = true;
@ -338,7 +342,7 @@ bool LottieOffsetModifier::modifyPath(PathCommand* inCmds, uint32_t inCmdsCnt, P
line(out, inCmds, inCmdsCnt, inPts, iPt, iCmd, state, offset, false);
} else if (inCmds[iCmd] == PathCommand::CubicTo) {
//cubic degenerated to a line
if (tvg::zero(inPts[iPt - 1] - inPts[iPt]) || tvg::zero(inPts[iPt + 1] - inPts[iPt + 2])) {
if (_colinear(inPts + iPt - 1)) {
++iPt;
line(out, inCmds, inCmdsCnt, inPts, iPt, iCmd, state, offset, true);
++iPt;
@ -350,7 +354,7 @@ bool LottieOffsetModifier::modifyPath(PathCommand* inCmds, uint32_t inCmdsCnt, P
auto& bezier = stack.last();
auto len = tvg::length(bezier.start - bezier.ctrl1) + tvg::length(bezier.ctrl1 - bezier.ctrl2) + tvg::length(bezier.ctrl2 - bezier.end);
if (len > threshold * bezier.length()) {
if (len > threshold * bezier.length() && len > 1.0f) {
Bezier next;
bezier.split(0.5f, next);
stack.push(next);
@ -358,9 +362,19 @@ bool LottieOffsetModifier::modifyPath(PathCommand* inCmds, uint32_t inCmdsCnt, P
}
stack.pop();
auto line1 = _offset(bezier.start, bezier.ctrl1, offset);
degeneratedLine1 = _zero(bezier.start, bezier.ctrl1);
auto line1 = degeneratedLine1 ? state.line : _offset(bezier.start, bezier.ctrl1, offset);
auto line2 = _offset(bezier.ctrl1, bezier.ctrl2, offset);
auto line3 = _offset(bezier.ctrl2, bezier.end, offset);
//line3 from the previous iteration was degenerated to a point - calculate intersection with the last valid line (state.line)
if (degeneratedLine3) {
_intersect(degeneratedLine1 ? line2 : line1, state.line, intersect, inside);
out.pts.push(intersect);
out.pts.push(intersect);
}
degeneratedLine3 = _zero(bezier.ctrl2, bezier.end);
auto& line3 = state.line = degeneratedLine3 ? line2 : _offset(bezier.ctrl2, bezier.end, offset);
if (state.moveto) {
out.cmds.push(PathCommand::MoveTo);
@ -370,19 +384,22 @@ bool LottieOffsetModifier::modifyPath(PathCommand* inCmds, uint32_t inCmdsCnt, P
state.moveto = false;
}
bool inside{};
Point intersect{};
_intersect(line1, line2, intersect, inside);
out.pts.push(intersect);
_intersect(line2, line3, intersect, inside);
out.pts.push(intersect);
out.pts.push(line3.pt2);
if (degeneratedLine1) out.pts.push(out.pts.last());
else {
_intersect(line1, line2, intersect, inside);
out.pts.push(intersect);
}
if (!degeneratedLine3) {
_intersect(line2, line3, intersect, inside);
out.pts.push(intersect);
out.pts.push(line3.pt2);
}
out.cmds.push(PathCommand::CubicTo);
}
iPt += 3;
}
else {
} else {
if (!_zero(inPts[iPt - 1], inPts[state.movetoInIndex])) {
out.cmds.push(PathCommand::LineTo);
corner(out, state.line, state.firstLine, state.movetoOutIndex, true);