renderer: handle edge cases for trimming with dashing

- In cases where the begin and end values of trimming did not
result in trimming (end - begin > 1), trimming was ignored.
However, when the stroke is also dashed, this case affects
the shift of the point where the first dash becomes visible.

- Trimming that passes through the curve's start point (like -0.1:0.1)
requires passing through the curve twice. The points obtained from
both passes must be joined - visible when dashing
Cases for simultaneous = true have been handled.

@Issue: https://github.com/thorvg/thorvg/issues/3192

src/loaders/lottie/tvgLottieModel.cpp

@@ -236,15 +236,16 @@ void LottieTrimpath::segment(float frameNo, float& start, float& end, Tween& twe
         end = 0.0f;
         return;
     }
-    if (tvg::equal(diff, 1.0f) || tvg::equal(diff, 2.0f)) {
+
+    //Even if the start and end values do not cause trimming, an offset > 0 can still affect dashing starting point
+    auto o = fmodf(this->offset(frameNo, tween, exps), 360.0f) / 360.0f;  //0 ~ 1
+    if (tvg::zero(o) && diff >= 1.0f) {
         start = 0.0f;
         end = 1.0f;
         return;
     }
 
     if (start > end) std::swap(start, end);
-
-    auto o = fmodf(this->offset(frameNo, tween, exps), 360.0f) / 360.0f;  //0 ~ 1
     start += o;
     end += o;
 }

src/renderer/tvgShape.h

@@ -211,10 +211,8 @@ struct Shape::Impl : Paint::Impl
 
     void strokeTrim(float begin, float end, bool simultaneous)
     {
-        if (fabsf(end - begin) >= 1.0f) {
+        //Even if there is no trimming effect, begin can still affect dashing starting point
-            begin = 0.0f;
+        if (fabsf(end - begin) >= 1.0f) end = begin + 1.0f;
-            end = 1.0f;
-        }
 
         if (!rs.stroke) {
             if (begin == 0.0f && end == 1.0f) return;

src/renderer/tvgTrimPath.cpp

@@ -162,7 +162,7 @@ static void _add(const PathCommand* cmds, const Point* pts, const Point& moveTo,
 }
 
 
-static void _trimPath(const PathCommand* inCmds, uint32_t inCmdsCnt, const Point* inPts, TVG_UNUSED uint32_t inPtsCnt, float trimStart, float trimEnd, RenderPath& out)
+static void _trimPath(const PathCommand* inCmds, uint32_t inCmdsCnt, const Point* inPts, TVG_UNUSED uint32_t inPtsCnt, float trimStart, float trimEnd, RenderPath& out, bool connect = false)
 {
     auto cmds = const_cast<PathCommand*>(inCmds);
     auto pts = const_cast<Point*>(inPts);
@@ -203,7 +203,7 @@ static void _trimPath(const PathCommand* inCmds, uint32_t inCmdsCnt, const Point
         ++cmds;
     };
 
-    bool start = true;
+    auto start = !connect;
     for (uint32_t i = 0; i < inCmdsCnt; ++i) {
         auto dLen = _length();
 
@@ -234,15 +234,18 @@ static void _trimPath(const PathCommand* inCmds, uint32_t inCmdsCnt, const Point
 }
 
 
-static void _trim(const PathCommand* inCmds, uint32_t inCmdsCnt, const Point* inPts, uint32_t inPtsCnt, float begin, float end, RenderPath& out)
+static void _trim(const PathCommand* inCmds, uint32_t inCmdsCnt, const Point* inPts, uint32_t inPtsCnt, float begin, float end, bool connect, RenderPath& out)
 {
     auto totalLength = _pathLength(inCmds, inCmdsCnt, inPts, inPtsCnt);
     auto trimStart = begin * totalLength;
     auto trimEnd = end * totalLength;
 
-    if (trimStart > trimEnd) {
+    if (fabsf(begin - end) < EPSILON) {
         _trimPath(inCmds, inCmdsCnt, inPts, inPtsCnt, trimStart, totalLength, out);
-        _trimPath(inCmds, inCmdsCnt, inPts, inPtsCnt, 0.0f, trimEnd, out);
+        _trimPath(inCmds, inCmdsCnt, inPts, inPtsCnt, 0.0f, trimStart, out, connect);
+    } else if (begin > end) {
+        _trimPath(inCmds, inCmdsCnt, inPts, inPtsCnt, trimStart, totalLength, out);
+        _trimPath(inCmds, inCmdsCnt, inPts, inPtsCnt, 0.0f, trimEnd, out, connect);
     } else {
         _trimPath(inCmds, inCmdsCnt, inPts, inPtsCnt, trimStart, trimEnd, out);
     }
@@ -280,11 +283,11 @@ bool TrimPath::valid() const
 
 bool TrimPath::trim(const RenderPath& in, RenderPath& out) const
 {
+    if (in.pts.count < 2 || tvg::zero(begin - end)) return false;
+
     float begin = this->begin, end = this->end;
     _get(begin, end);
 
-    if (in.pts.count < 2 || tvg::zero(begin - end)) return false;
-
     out.cmds.reserve(in.cmds.count * 2);
     out.pts.reserve(in.pts.count * 2);
 
@@ -298,7 +301,7 @@ bool TrimPath::trim(const RenderPath& in, RenderPath& out) const
         while (i < in.cmds.count) {
             switch (in.cmds[i]) {
                 case PathCommand::MoveTo: {
-                    if (startCmds != cmds) _trim(startCmds, cmds - startCmds, startPts, pts - startPts, begin, end, out);
+                    if (startCmds != cmds) _trim(startCmds, cmds - startCmds, startPts, pts - startPts, begin, end, *(cmds - 1) == PathCommand::Close, out);
                     startPts = pts;
                     startCmds = cmds;
                     ++pts;
@@ -317,7 +320,7 @@ bool TrimPath::trim(const RenderPath& in, RenderPath& out) const
                 }
                 case PathCommand::Close: {
                     ++cmds;
-                    if (startCmds != cmds) _trim(startCmds, cmds - startCmds, startPts, pts - startPts, begin, end, out);
+                    if (startCmds != cmds) _trim(startCmds, cmds - startCmds, startPts, pts - startPts, begin, end, *(cmds - 1) == PathCommand::Close, out);
                     startPts = pts;
                     startCmds = cmds;
                     break;
@@ -325,9 +328,9 @@ bool TrimPath::trim(const RenderPath& in, RenderPath& out) const
             }
             i++;
         }
-        if (startCmds != cmds) _trim(startCmds, cmds - startCmds, startPts, pts - startPts, begin, end, out);
+        if (startCmds != cmds) _trim(startCmds, cmds - startCmds, startPts, pts - startPts, begin, end, *(cmds - 1) == PathCommand::Close, out);
     } else {
-        _trim(in.cmds.data, in.cmds.count, in.pts.data, in.pts.count, begin, end, out);
+        _trim(in.cmds.data, in.cmds.count, in.pts.data, in.pts.count, begin, end, false, out);
     }
 
     return out.pts.count >= 2;