sw_engine: fix trimming

For the 'simultaneous' trimming option, the maximum
stroke length from all subpaths was determined and
used to scale the trim of each subpath. As a result,
if the subpaths had different lengths, this scaling
was incorrect.
Now, the length is determined separately for each
subpath and is used to scale the trimming of its stroke.

@Issue: https://github.com/thorvg/thorvg/issues/2335

src/renderer/sw_engine/tvgSwShape.cpp

@@ -245,7 +245,86 @@ static void _dashMoveTo(SwDashStroke& dash, uint32_t offIdx, float offset, const
 }
 
 
-static SwOutline* _genDashOutline(const RenderShape* rshape, const Matrix* transform, float length, SwMpool* mpool, unsigned tid)
+static void _trimPattern(SwDashStroke* dash, const RenderShape* rshape, float length)
+{
+    auto begin = length * rshape->stroke->trim.begin;
+    auto end = length * rshape->stroke->trim.end;
+
+    //default
+    if (end > begin) {
+        if (begin > 0.0f) dash->cnt = 4;
+        else dash->cnt = 2;
+        //looping
+    } else dash->cnt = 3;
+
+    if (dash->cnt == 2) {
+        dash->pattern[0] = end - begin;
+        dash->pattern[1] = length - (end - begin);
+    } else if (dash->cnt == 3) {
+        dash->pattern[0] = end;
+        dash->pattern[1] = (begin - end);
+        dash->pattern[2] = length - begin;
+    } else {
+        dash->pattern[0] = 0;     //zero dash to start with a space.
+        dash->pattern[1] = begin;
+        dash->pattern[2] = end - begin;
+        dash->pattern[3] = length - end;
+    }
+}
+
+
+static float _outlineLength(const RenderShape* rshape, uint32_t shiftPts, uint32_t shiftCmds, bool subpath)
+{
+    const PathCommand* cmds = rshape->path.cmds.data + shiftCmds;
+    auto cmdCnt = rshape->path.cmds.count - shiftCmds;
+    const Point* pts = rshape->path.pts.data + shiftPts;
+    auto ptsCnt = rshape->path.pts.count - shiftPts;
+
+    //No actual shape data
+    if (cmdCnt <= 0 || ptsCnt <= 0) return 0.0f;
+
+    const Point* close = nullptr;
+    auto length = 0.0f;
+
+    //must begin with moveTo
+    if (cmds[0] == PathCommand::MoveTo) {
+        close = pts;
+        cmds++;
+        pts++;
+        cmdCnt--;
+    }
+
+    while (cmdCnt-- > 0) {
+        switch (*cmds) {
+            case PathCommand::Close: {
+                length += mathLength(pts - 1, close);
+                if (subpath) return length;
+                break;
+            }
+            case PathCommand::MoveTo: {
+                if (subpath) return length;
+                close = pts;
+                ++pts;
+                break;
+            }
+            case PathCommand::LineTo: {
+                length += mathLength(pts - 1, pts);
+                ++pts;
+                break;
+            }
+            case PathCommand::CubicTo: {
+                length += bezLength({*(pts - 1), *pts, *(pts + 1), *(pts + 2)});
+                pts += 3;
+                break;
+            }
+        }
+        ++cmds;
+    }
+    return length;
+}
+
+
+static SwOutline* _genDashOutline(const RenderShape* rshape, const Matrix* transform, bool trimmed, SwMpool* mpool, unsigned tid)
 {
     const PathCommand* cmds = rshape->path.cmds.data;
     auto cmdCnt = rshape->path.cmds.count;
@@ -255,49 +334,23 @@ static SwOutline* _genDashOutline(const RenderShape* rshape, const Matrix* trans
     //No actual shape data
     if (cmdCnt == 0 || ptsCnt == 0) return nullptr;
 
+    auto startPts = pts;
+    auto startCmds = cmds;
+
     SwDashStroke dash;
     auto offset = 0.0f;
-    auto trimmed = false;
-
     dash.cnt = rshape->strokeDash((const float**)&dash.pattern, &offset);
+    auto simultaneous = rshape->stroke->trim.simultaneous;
 
-    //dash by trimming.
+    if (dash.cnt == 0) {
-    if (length > 0.0f && dash.cnt == 0) {
+        if (trimmed) dash.pattern = (float*)malloc(sizeof(float) * 4);
-        auto begin = length * rshape->stroke->trim.begin;
+        else return nullptr;
-        auto end = length * rshape->stroke->trim.end;
-
-        //TODO: mix trimming + dash style
-
-        //default
-        if (end > begin) {
-            if (begin > 0.0f) dash.cnt += 4;
-            else dash.cnt += 2;
-        //looping
-        } else dash.cnt += 3;
-
-        dash.pattern = (float*)malloc(sizeof(float) * dash.cnt);
-
-        if (dash.cnt == 2) {
-            dash.pattern[0] = end - begin;
-            dash.pattern[1] = length - (end - begin);
-        } else if (dash.cnt == 3) {
-            dash.pattern[0] = end;
-            dash.pattern[1] = (begin - end);
-            dash.pattern[2] = length - begin;
     } else {
-            dash.pattern[0] = 0;     //zero dash to start with a space.
+        //TODO: handle dash + trim - for now trimming ignoring is forced
-            dash.pattern[1] = begin;
+        trimmed = false;
-            dash.pattern[2] = end - begin;
-            dash.pattern[3] = length - end;
     }
 
-        trimmed = true;
+    //offset
-    //just a dasy style.
-    } else {
-        if (dash.cnt == 0) return nullptr;
-    }
-
-    //offset?
     auto patternLength = 0.0f;
     uint32_t offIdx = 0;
     if (!mathZero(offset)) {
@@ -319,6 +372,7 @@ static SwOutline* _genDashOutline(const RenderShape* rshape, const Matrix* trans
 
     //must begin with moveTo
     if (cmds[0] == PathCommand::MoveTo) {
+        if (trimmed) _trimPattern(&dash, rshape, _outlineLength(rshape, 0, 0, simultaneous));
         _dashMoveTo(dash, offIdx, offset, pts);
         cmds++;
         pts++;
@@ -331,9 +385,12 @@ static SwOutline* _genDashOutline(const RenderShape* rshape, const Matrix* trans
                 break;
             }
             case PathCommand::MoveTo: {
-                if (rshape->stroke->trim.simultaneous) _dashMoveTo(dash, offIdx, offset, pts);
+                if (trimmed) {
-                else _dashMoveTo(dash, pts);
+                    if (simultaneous) {
-
+                        _trimPattern(&dash, rshape, _outlineLength(rshape, pts - startPts, cmds - startCmds, true));
+                        _dashMoveTo(dash, offIdx, offset, pts);
+                    } else _dashMoveTo(dash, pts);
+                } else _dashMoveTo(dash, offIdx, offset, pts);
                 ++pts;
                 break;
             }
@@ -359,56 +416,6 @@ static SwOutline* _genDashOutline(const RenderShape* rshape, const Matrix* trans
 }
 
 
-static float _outlineLength(const RenderShape* rshape)
-{
-    const PathCommand* cmds = rshape->path.cmds.data;
-    auto cmdCnt = rshape->path.cmds.count;
-    const Point* pts = rshape->path.pts.data;
-    auto ptsCnt = rshape->path.pts.count;
-
-    //No actual shape data
-    if (cmdCnt == 0 || ptsCnt == 0) return 0.0f;
-
-    const Point* close = nullptr;
-    auto length = 0.0f;
-    auto slength = -1.0f;
-    auto simultaneous = rshape->stroke->trim.simultaneous;
-
-    //Compute the whole length
-    while (cmdCnt-- > 0) {
-        switch (*cmds) {
-            case PathCommand::Close: {
-                length += mathLength(pts - 1, close);
-                //retrieve the max length of the shape if the simultaneous mode.
-                if (simultaneous) {
-                    if (slength < length) slength = length;
-                    length = 0.0f;
-                }
-                break;
-            }
-            case PathCommand::MoveTo: {
-                close = pts;
-                ++pts;
-                break;
-            }
-            case PathCommand::LineTo: {
-                length += mathLength(pts - 1, pts);
-                ++pts;
-                break;
-            }
-            case PathCommand::CubicTo: {
-                length += bezLength({*(pts - 1), *pts, *(pts + 1), *(pts + 2)});
-                pts += 3;
-                break;
-            }
-        }
-        ++cmds;
-    }
-    if (simultaneous && slength > length) return slength;
-    else return length;
-}
-
-
 static bool _axisAlignedRect(const SwOutline* outline)
 {
     //Fast Track: axis-aligned rectangle?
@@ -585,11 +592,10 @@ bool shapeGenStrokeRle(SwShape* shape, const RenderShape* rshape, const Matrix*
     auto dashStroking = false;
     auto ret = true;
 
-    auto length = rshape->strokeTrim() ? _outlineLength(rshape) : 0.0f;
-
     //Dash style (+trimming)
-    if (rshape->stroke->dashCnt > 0 || length > 0) {
+    auto trimmed = rshape->strokeTrim();
-        shapeOutline = _genDashOutline(rshape, transform, length, mpool, tid);
+    if (rshape->stroke->dashCnt > 0 || trimmed) {
+        shapeOutline = _genDashOutline(rshape, transform, trimmed, mpool, tid);
         if (!shapeOutline) return false;
         dashStroking = true;
     //Normal style