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thorvg/src/loaders/lottie/tvgLottieModifier.cpp
Mira Grudzinska 2679880bc3
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lottie: ensure proper shape closure 
- Ensured proper closure of star and polygon shapes.
The start and end points now match - in cases with
degenerate bezier curves, the second-to-last point
is also aligned.
Proper shape closure is necessary for modifiers like
offset (future pucker bloat). If the start and end
points aren’t equal (within the comparison function’s
precision), the shape will be closed with a straight
line - and during offsetting, that line will become
visible, even though it’s not intended.

- Use of the internal _zero() function for point equality check
in modifiers algs led to incorrect results when p2.x or p2.y
was zero (division by zero).
The intent was to treat nearly identical points as equal, but
this approach was flawed - at the modifier stage, it’s no longer
possible to tell if small gaps are intentional or just due to
limited numerical precision (as seen for example in the difference
between the start and end points of star/polygon shapes).
2025-06-20 10:39:12 +09:00

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/*
* Copyright (c) 2024 - 2025 the ThorVG project. All rights reserved.
* Permission is hereby granted, free of charge, to any person obtaining a copy
* of this software and associated documentation files (the "Software"), to deal
* in the Software without restriction, including without limitation the rights
* to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
* copies of the Software, and to permit persons to whom the Software is
* furnished to do so, subject to the following conditions:
* The above copyright notice and this permission notice shall be included in all
* copies or substantial portions of the Software.
* THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
* IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
* FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
* AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
* LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
* OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE
* SOFTWARE.
*/
#include "tvgLottieModifier.h"
/************************************************************************/
/* Internal Class Implementation */
/************************************************************************/
static bool _colinear(const Point* p)
{
return tvg::zero(*p - *(p + 1)) && tvg::zero(*(p + 2) - *(p + 3));
}
static void _roundCorner(Array<PathCommand>& cmds, Array<Point>& pts, Point& prev, Point& curr, Point& next, float r)
{
auto lenPrev = length(prev - curr);
auto rPrev = lenPrev > 0.0f ? 0.5f * std::min(lenPrev * 0.5f, r) / lenPrev : 0.0f;
auto lenNext = length(next - curr);
auto rNext = lenNext > 0.0f ? 0.5f * std::min(lenNext * 0.5f, r) / lenNext : 0.0f;
auto dPrev = rPrev * (curr - prev);
auto dNext = rNext * (curr - next);
pts.push(curr - 2.0f * dPrev);
pts.push(curr - dPrev);
pts.push(curr - dNext);
pts.push(curr - 2.0f * dNext);
cmds.push(PathCommand::LineTo);
cmds.push(PathCommand::CubicTo);
}
static bool _intersect(Line& line1, Line& line2, Point& intersection, bool& inside)
{
if (tvg::zero(line1.pt2 - line2.pt1)) {
intersection = line1.pt2;
inside = true;
return true;
}
constexpr float epsilon = 1e-3f;
float denom = (line1.pt2.x - line1.pt1.x) * (line2.pt2.y - line2.pt1.y) - (line1.pt2.y - line1.pt1.y) * (line2.pt2.x - line2.pt1.x);
if (fabsf(denom) < epsilon) return false;
float t = ((line2.pt1.x - line1.pt1.x) * (line2.pt2.y - line2.pt1.y) - (line2.pt1.y - line1.pt1.y) * (line2.pt2.x - line2.pt1.x)) / denom;
float u = ((line2.pt1.x - line1.pt1.x) * (line1.pt2.y - line1.pt1.y) - (line2.pt1.y - line1.pt1.y) * (line1.pt2.x - line1.pt1.x)) / denom;
intersection.x = line1.pt1.x + t * (line1.pt2.x - line1.pt1.x);
intersection.y = line1.pt1.y + t * (line1.pt2.y - line1.pt1.y);
inside = t >= -epsilon && t <= 1.0f + epsilon && u >= -epsilon && u <= 1.0f + epsilon;
return true;
}
static Line _offset(Point& p1, Point& p2, float offset)
{
auto scaledNormal = normal(p1, p2) * offset;
return {p1 + scaledNormal, p2 + scaledNormal};
}
static bool _clockwise(Point* pts, uint32_t n)
{
auto area = 0.0f;
for (uint32_t i = 0; i < n - 1; i++) {
area += cross(pts[i], pts[i + 1]);
}
area += cross(pts[n - 1], pts[0]);;
return area < 0.0f;
}
void LottieOffsetModifier::corner(RenderPath& out, Line& line, Line& nextLine, uint32_t movetoOutIndex, bool nextClose)
{
bool inside{};
Point intersect{};
if (_intersect(line, nextLine, intersect, inside)) {
if (inside) {
if (nextClose) out.pts[movetoOutIndex] = intersect;
out.pts.push(intersect);
} else {
out.pts.push(line.pt2);
if (join == StrokeJoin::Round) {
out.cmds.push(PathCommand::CubicTo);
out.pts.push((line.pt2 + intersect) * 0.5f);
out.pts.push((nextLine.pt1 + intersect) * 0.5f);
out.pts.push(nextLine.pt1);
} else if (join == StrokeJoin::Miter) {
auto norm = normal(line.pt1, line.pt2);
auto nextNorm = normal(nextLine.pt1, nextLine.pt2);
auto miterDirection = (norm + nextNorm) / length(norm + nextNorm);
if (1.0f <= miterLimit * fabsf(miterDirection.x * norm.x + miterDirection.y * norm.y)) {
out.cmds.push(PathCommand::LineTo);
out.pts.push(intersect);
}
out.cmds.push(PathCommand::LineTo);
out.pts.push(nextLine.pt1);
} else {
out.cmds.push(PathCommand::LineTo);
out.pts.push(nextLine.pt1);
}
}
} else out.pts.push(line.pt2);
}
void LottieOffsetModifier::line(RenderPath& out, PathCommand* inCmds, uint32_t inCmdsCnt, Point* inPts, uint32_t& curPt, uint32_t curCmd, State& state, float offset, bool degenerated)
{
if (tvg::zero(inPts[curPt - 1] - inPts[curPt])) {
++curPt;
return;
}
if (inCmds[curCmd - 1] != PathCommand::LineTo) state.line = _offset(inPts[curPt - 1], inPts[curPt], offset);
if (state.moveto) {
out.cmds.push(PathCommand::MoveTo);
state.movetoOutIndex = out.pts.count;
out.pts.push(state.line.pt1);
state.firstLine = state.line;
state.moveto = false;
}
auto nonDegeneratedCubic = [&](uint32_t cmd, uint32_t pt) {
return inCmds[cmd] == PathCommand::CubicTo && !tvg::zero(inPts[pt] - inPts[pt + 1]) && !tvg::zero(inPts[pt + 2] - inPts[pt + 3]);
};
out.cmds.push(PathCommand::LineTo);
if (curCmd + 1 == inCmdsCnt || inCmds[curCmd + 1] == PathCommand::MoveTo || nonDegeneratedCubic(curCmd + 1, curPt + degenerated)) {
out.pts.push(state.line.pt2);
++curPt;
return;
}
Line nextLine = state.firstLine;
if (inCmds[curCmd + 1] == PathCommand::LineTo) nextLine = _offset(inPts[curPt + degenerated], inPts[curPt + 1 + degenerated], offset);
else if (inCmds[curCmd + 1] == PathCommand::CubicTo) nextLine = _offset(inPts[curPt + 1 + degenerated], inPts[curPt + 2 + degenerated], offset);
else if (inCmds[curCmd + 1] == PathCommand::Close && !tvg::zero(inPts[curPt + degenerated] - inPts[state.movetoInIndex + degenerated]))
nextLine = _offset(inPts[curPt + degenerated], inPts[state.movetoInIndex + degenerated], offset);
corner(out, state.line, nextLine, state.movetoOutIndex, inCmds[curCmd + 1] == PathCommand::Close);
state.line = nextLine;
++curPt;
}
/************************************************************************/
/* External Class Implementation */
/************************************************************************/
bool LottieRoundnessModifier::modifyPath(PathCommand* inCmds, uint32_t inCmdsCnt, Point* inPts, uint32_t inPtsCnt, Matrix* transform, RenderPath& out)
{
buffer->clear();
auto& path = (next) ? *buffer : out;
path.cmds.reserve(inCmdsCnt * 2);
path.pts.reserve((uint32_t)(inPtsCnt * 1.5));
auto pivot = path.pts.count;
uint32_t startIndex = 0;
for (uint32_t iCmds = 0, iPts = 0; iCmds < inCmdsCnt; ++iCmds) {
switch (inCmds[iCmds]) {
case PathCommand::MoveTo: {
startIndex = path.pts.count;
path.cmds.push(PathCommand::MoveTo);
path.pts.push(inPts[iPts++]);
break;
}
case PathCommand::CubicTo: {
if (iCmds < inCmdsCnt - 1 && _colinear(inPts + iPts - 1)) {
auto& prev = inPts[iPts - 1];
auto& curr = inPts[iPts + 2];
if (inCmds[iCmds + 1] == PathCommand::CubicTo && _colinear(inPts + iPts + 2)) {
_roundCorner(path.cmds, path.pts, prev, curr, inPts[iPts + 5], r);
iPts += 3;
break;
} else if (inCmds[iCmds + 1] == PathCommand::Close) {
_roundCorner(path.cmds, path.pts, prev, curr, inPts[2], r);
path.pts[startIndex] = path.pts.last();
iPts += 3;
break;
}
}
path.cmds.push(PathCommand::CubicTo);
path.pts.push(inPts[iPts++]);
path.pts.push(inPts[iPts++]);
path.pts.push(inPts[iPts++]);
break;
}
case PathCommand::Close: {
path.cmds.push(PathCommand::Close);
break;
}
default: break;
}
}
if (transform) {
for (auto i = pivot; i < path.pts.count; ++i) {
path.pts[i] *= *transform;
}
}
if (next) return next->modifyPath(path.cmds.data, path.cmds.count, path.pts.data, path.pts.count, transform, out);
return true;
}
bool LottieRoundnessModifier::modifyPolystar(RenderPath& in, RenderPath& out, float outerRoundness, bool hasRoundness)
{
constexpr auto ROUNDED_POLYSTAR_MAGIC_NUMBER = 0.47829f;
buffer->clear();
auto& path = (next) ? *buffer : out;
auto len = length(in.pts[1] - in.pts[2]);
auto r = len > 0.0f ? ROUNDED_POLYSTAR_MAGIC_NUMBER * std::min(len * 0.5f, this->r) / len : 0.0f;
if (hasRoundness) {
path.cmds.grow((uint32_t)(1.5 * in.cmds.count));
path.pts.grow((uint32_t)(4.5 * in.cmds.count));
int start = 3 * tvg::zero(outerRoundness);
path.cmds.push(PathCommand::MoveTo);
path.pts.push(in.pts[start]);
for (uint32_t i = 1 + start; i < in.pts.count; i += 6) {
auto& prev = in.pts[i];
auto& curr = in.pts[i + 2];
auto& next = (i < in.pts.count - start) ? in.pts[i + 4] : in.pts[2];
auto& nextCtrl = (i < in.pts.count - start) ? in.pts[i + 5] : in.pts[3];
auto dNext = r * (curr - next);
auto dPrev = r * (curr - prev);
auto p0 = curr - 2.0f * dPrev;
auto p1 = curr - dPrev;
auto p2 = curr - dNext;
auto p3 = curr - 2.0f * dNext;
path.cmds.push(PathCommand::CubicTo);
path.pts.push(prev); path.pts.push(p0); path.pts.push(p0);
path.cmds.push(PathCommand::CubicTo);
path.pts.push(p1); path.pts.push(p2); path.pts.push(p3);
path.cmds.push(PathCommand::CubicTo);
path.pts.push(p3); path.pts.push(next); path.pts.push(nextCtrl);
}
} else {
path.cmds.grow(2 * in.cmds.count);
path.pts.grow(4 * in.cmds.count);
auto dPrev = r * (in.pts[1] - in.pts[0]);
auto p = in.pts[0] + 2.0f * dPrev;
path.cmds.push(PathCommand::MoveTo);
path.pts.push(p);
for (uint32_t i = 1; i < in.pts.count; ++i) {
auto& curr = in.pts[i];
auto& next = (i == in.pts.count - 1) ? in.pts[1] : in.pts[i + 1];
auto dNext = r * (curr - next);
auto p0 = curr - 2.0f * dPrev;
auto p1 = curr - dPrev;
auto p2 = curr - dNext;
auto p3 = curr - 2.0f * dNext;
path.cmds.push(PathCommand::LineTo);
path.pts.push(p0);
path.cmds.push(PathCommand::CubicTo);
path.pts.push(p1); path.pts.push(p2); path.pts.push(p3);
dPrev = -1.0f * dNext;
}
}
path.cmds.push(PathCommand::Close);
if (next) return next->modifyPolystar(path, out, outerRoundness, hasRoundness);
return true;
}
bool LottieRoundnessModifier::modifyRect(Point& size, float& r)
{
r = std::min(this->r, std::max(size.x, size.y) * 0.5f);
return true;
}
bool LottieOffsetModifier::modifyPath(PathCommand* inCmds, uint32_t inCmdsCnt, Point* inPts, uint32_t inPtsCnt, TVG_UNUSED Matrix* transform, RenderPath& out)
{
if (next) TVGERR("LOTTIE", "Offset has a next modifier?");
out.cmds.reserve(inCmdsCnt * 2);
out.pts.reserve(inPtsCnt * (join == StrokeJoin::Round ? 4 : 2));
Array<Bezier> stack{5};
State state;
auto offset = _clockwise(inPts, inPtsCnt) ? this->offset : -this->offset;
auto threshold = 1.0f / fabsf(offset) + 1.0f;
for (uint32_t iCmd = 0, iPt = 0; iCmd < inCmdsCnt; ++iCmd) {
if (inCmds[iCmd] == PathCommand::MoveTo) {
state.moveto = true;
state.movetoInIndex = iPt++;
} else if (inCmds[iCmd] == PathCommand::LineTo) {
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])) {
++iPt;
line(out, inCmds, inCmdsCnt, inPts, iPt, iCmd, state, offset, true);
++iPt;
continue;
}
stack.push({inPts[iPt - 1], inPts[iPt], inPts[iPt + 1], inPts[iPt + 2]});
while (!stack.empty()) {
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()) {
Bezier next;
bezier.split(0.5f, next);
stack.push(next);
continue;
}
stack.pop();
auto line1 = _offset(bezier.start, bezier.ctrl1, offset);
auto line2 = _offset(bezier.ctrl1, bezier.ctrl2, offset);
auto line3 = _offset(bezier.ctrl2, bezier.end, offset);
if (state.moveto) {
out.cmds.push(PathCommand::MoveTo);
state.movetoOutIndex = out.pts.count;
out.pts.push(line1.pt1);
state.firstLine = line1;
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);
out.cmds.push(PathCommand::CubicTo);
}
iPt += 3;
}
else {
if (!tvg::zero(inPts[iPt - 1] - inPts[state.movetoInIndex])) {
out.cmds.push(PathCommand::LineTo);
corner(out, state.line, state.firstLine, state.movetoOutIndex, true);
}
out.cmds.push(PathCommand::Close);
}
}
return true;
}
bool LottieOffsetModifier::modifyPolystar(RenderPath& in, RenderPath& out, TVG_UNUSED float, TVG_UNUSED bool)
{
return modifyPath(in.cmds.data, in.cmds.count, in.pts.data, in.pts.count, nullptr, out);
}
bool LottieOffsetModifier::modifyRect(RenderPath& in, RenderPath& out)
{
return modifyPath(in.cmds.data, in.cmds.count, in.pts.data, in.pts.count, nullptr, out);
}
bool LottieOffsetModifier::modifyEllipse(Point& radius)
{
radius.x += offset;
radius.y += offset;
return true;
}
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