sw_engine/stroke: enhanced the quality of the dash line corners.

Previously, the engine didn't properly cover the dash line corner styles
because it considered a new line to start at the corner.

This update modifies the logic to recognize curved lines
as a single line, including the corners.

There may still be some quality issues,
but it's an improvement over the previous version.

@Issue: https://github.com/thorvg/thorvg/issues/121

src/renderer/sw_engine/tvgSwCommon.h

@@ -205,6 +205,7 @@ struct SwDashStroke
     float* pattern = nullptr;
     uint32_t cnt = 0;
     bool curOpGap = false;
+    bool move = true;
 };
 
 struct SwShape

src/renderer/sw_engine/tvgSwShape.cpp

@@ -121,7 +121,10 @@ static void _dashLineTo(SwDashStroke& dash, const Point* to, const Matrix* trans
     if (len < dash.curLen) {
         dash.curLen -= len;
         if (!dash.curOpGap) {
-            _outlineMoveTo(*dash.outline, &dash.ptCur, transform);
+            if (dash.move) {
+                _outlineMoveTo(*dash.outline, &dash.ptCur, transform);
+                dash.move = false;
+            }
             _outlineLineTo(*dash.outline, to, transform);
         }
     } else {
@@ -131,7 +134,10 @@ static void _dashLineTo(SwDashStroke& dash, const Point* to, const Matrix* trans
                 len -= dash.curLen;
                 _lineSplitAt(cur, dash.curLen, left, right);
                 if (!dash.curOpGap) {
-                    _outlineMoveTo(*dash.outline, &left.pt1, transform);
+                    if (dash.move || dash.pattern[dash.curIdx] - dash.curLen < FLT_EPSILON) {
+                        _outlineMoveTo(*dash.outline, &left.pt1, transform);
+                        dash.move = false;
+                    }
                     _outlineLineTo(*dash.outline, &left.pt2, transform);
                 }
             } else {
@@ -142,11 +148,15 @@ static void _dashLineTo(SwDashStroke& dash, const Point* to, const Matrix* trans
             dash.curOpGap = !dash.curOpGap;
             cur = right;
             dash.ptCur = cur.pt1;
+            dash.move = true;
         }
         //leftovers
         dash.curLen -= len;
         if (!dash.curOpGap) {
-            _outlineMoveTo(*dash.outline, &cur.pt1, transform);
+            if (dash.move) {
+                _outlineMoveTo(*dash.outline, &cur.pt1, transform);
+                dash.move = false;
+            }
             _outlineLineTo(*dash.outline, &cur.pt2, transform);
         }
         if (dash.curLen < 1 && TO_SWCOORD(len) > 1) {
@@ -168,21 +178,22 @@ static void _dashCubicTo(SwDashStroke& dash, const Point* ctrl1, const Point* ct
     if (len < dash.curLen) {
         dash.curLen -= len;
         if (!dash.curOpGap) {
-            _outlineMoveTo(*dash.outline, &dash.ptCur, transform);
+            if (dash.move) {
+                _outlineMoveTo(*dash.outline, &dash.ptCur, transform);
+                dash.move = false;
+            }
             _outlineCubicTo(*dash.outline, ctrl1, ctrl2, to, transform);
         }
     } else {
-        bool begin = true;          //starting with move_to
         while (len > dash.curLen) {
             Bezier left, right;
             if (dash.curLen > 0) {
                 len -= dash.curLen;
                 bezSplitAt(cur, dash.curLen, left, right);
                 if (!dash.curOpGap) {
-                    // leftovers from a previous command don't require moveTo
+                    if (dash.move || dash.pattern[dash.curIdx] - dash.curLen < FLT_EPSILON) {
-                    if (begin || dash.pattern[dash.curIdx] - dash.curLen < FLT_EPSILON) {
                         _outlineMoveTo(*dash.outline, &left.start, transform);
-                        begin = false;
+                        dash.move = false;
                     }
                     _outlineCubicTo(*dash.outline, &left.ctrl1, &left.ctrl2, &left.end, transform);
                 }
@@ -194,11 +205,15 @@ static void _dashCubicTo(SwDashStroke& dash, const Point* ctrl1, const Point* ct
             dash.curOpGap = !dash.curOpGap;
             cur = right;
             dash.ptCur = right.start;
+            dash.move = true;
         }
         //leftovers
         dash.curLen -= len;
         if (!dash.curOpGap) {
-            _outlineMoveTo(*dash.outline, &cur.start, transform);
+            if (dash.move) {
+                _outlineMoveTo(*dash.outline, &cur.start, transform);
+                dash.move = false;
+            }
             _outlineCubicTo(*dash.outline, &cur.ctrl1, &cur.ctrl2, &cur.end, transform);
         }
         if (dash.curLen < 1 && TO_SWCOORD(len) > 1) {
@@ -212,6 +227,22 @@ static void _dashCubicTo(SwDashStroke& dash, const Point* ctrl1, const Point* ct
 }
 
 
+static void _dashClose(SwDashStroke& dash, const Matrix* transform)
+{
+    _dashLineTo(dash, &dash.ptStart, transform);
+}
+
+
+static void _dashMoveTo(SwDashStroke& dash, uint32_t offIdx, float offset, const Point* pts, const Matrix* transform)
+{
+    dash.curIdx = offIdx % dash.cnt;
+    dash.curLen = dash.pattern[dash.curIdx] - offset;
+    dash.curOpGap = offIdx % 2;
+    dash.ptStart = dash.ptCur = *pts;
+    dash.move = true;
+}
+
+
 static SwOutline* _genDashOutline(const RenderShape* rshape, const Matrix* transform, float length, SwMpool* mpool, unsigned tid)
 {
     const PathCommand* cmds = rshape->path.cmds.data;
@@ -261,7 +292,6 @@ static SwOutline* _genDashOutline(const RenderShape* rshape, const Matrix* trans
         trimmed = true;
     //just a dasy style.
     } else {
-
         if (dash.cnt == 0) return nullptr;
     }
 
@@ -303,15 +333,11 @@ static SwOutline* _genDashOutline(const RenderShape* rshape, const Matrix* trans
     while (cmdCnt-- > 0) {
         switch (*cmds) {
             case PathCommand::Close: {
-                _dashLineTo(dash, &dash.ptStart, transform);
+                _dashClose(dash, transform);
                 break;
             }
             case PathCommand::MoveTo: {
-                //reset the dash
+                _dashMoveTo(dash, offIdx, offset, pts, transform);
-                dash.curIdx = offIdx % dash.cnt;
-                dash.curLen = dash.pattern[dash.curIdx] - offset;
-                dash.curOpGap = offIdx % 2;
-                dash.ptStart = dash.ptCur = *pts;
                 ++pts;
                 break;
             }

src/renderer/sw_engine/tvgSwStroke.cpp

@@ -689,7 +689,6 @@ static void _endSubPath(SwStroke& stroke)
 
         //No specific corner processing is required if the turn is 0
         if (turn != 0) {
-
             //when we turn to the right, the inside is 0
             int32_t inside = 0;