api: handling values <= 0 in strokeDash() api

The API allows now values <= 0 for dashes and gaps. Negative values
are treated as zero. The exception is when all provided values
are <= 0, in which case the dash is ignored.
This fixes the issue when dash = 0 was provided for strokes with round
or butt caps - the dot was not drawn, even though it should have been.

docs: the strokeDash API behavior's clarification for odd numbers
of values in dashPattern and refinement of the accepted values.

inc/thorvg.h

@@ -1083,14 +1083,17 @@ public:
     /**
      * @brief Sets the dash pattern of the stroke.
      *
-     * @param[in] dashPattern The array of consecutive pair values of the dash length and the gap length.
+     * @param[in] dashPattern An array of alternating dash and gap lengths.
      * @param[in] cnt The length of the @p dashPattern array.
-     * @param[in] offset The shift of the starting point within the repeating dash pattern from which the path's dashing begins.
+     * @param[in] offset The shift of the starting point within the repeating dash pattern, from which the pattern begins to be applied.
      *
-     * @retval Result::InvalidArguments In case @p dashPattern is @c nullptr and @p cnt > 0, @p cnt is zero, any of the dash pattern values is zero or less.
+     * @retval Result::InvalidArguments In case @p dashPattern is @c nullptr and @p cnt > 0 or @p dashPattern is not @c nullptr and @p cnt is zero.
      *
      * @note To reset the stroke dash pattern, pass @c nullptr to @p dashPattern and zero to @p cnt.
-     * @warning @p cnt must be greater than 1 if the dash pattern is valid.
+     * @note Values of @p dashPattern less than zero are treated as zero.
+     * @note If all values in the @p dashPattern are equal to or less than 0, the dash is ignored.
+     * @note If the @p dashPattern contains an odd number of elements, the sequence is repeated in the same
+     * order to form an even-length pattern, preserving the alternation of dashes and gaps.
      *
      * @since 1.0
      */

src/bindings/capi/thorvg_capi.h

@@ -1336,14 +1336,18 @@ TVG_API Tvg_Result tvg_shape_get_stroke_gradient(const Tvg_Paint* paint, Tvg_Gra
 * @brief Sets the shape's stroke dash pattern.
 *
 * @param[in] paint A Tvg_Paint pointer to the shape object.
-* @param[in] dashPattern The array of consecutive pair values of the dash length and the gap length.
+* @param[in] dashPattern An array of alternating dash and gap lengths.
 * @param[in] cnt The size of the @p dashPattern array.
-* @param[in] offset The shift of the starting point within the repeating dash pattern from which the path's dashing begins.
+* @param[in] offset The shift of the starting point within the repeating dash pattern, from which the pattern begins to be applied.
 *
 * @return Tvg_Result enumeration.
-* @retval TVG_RESULT_INVALID_ARGUMENT An invalid pointer passed as an argument and @p cnt > 0, the given length of the array is less than two or any of the @p dashPattern values is zero or less.
+* @retval TVG_RESULT_INVALID_ARGUMENT In case @p dashPattern is @c nullptr and @p cnt > 0 or @p dashPattern is not @c nullptr and @p cnt is zero.
 *
 * @note To reset the stroke dash pattern, pass @c nullptr to @p dashPattern and zero to @p cnt.
+* @note Values of @p dashPattern less than zero are treated as zero.
+* @note If all values in the @p dashPattern are equal to or less than 0, the dash is ignored.
+* @note If the @p dashPattern contains an odd number of elements, the sequence is repeated in the same
+* order to form an even-length pattern, preserving the alternation of dashes and gaps.
 * @since 1.0
 */
 TVG_API Tvg_Result tvg_shape_set_stroke_dash(Tvg_Paint* paint, const float* dashPattern, uint32_t cnt, float offset);

src/loaders/lottie/tvgLottieBuilder.cpp

@@ -219,15 +219,9 @@ static void _updateStroke(LottieStroke* stroke, float frameNo, RenderContext* ct
     ctx->propagator->strokeMiterlimit(stroke->miterLimit);
 
     if (stroke->dashattr) {
-        auto size = stroke->dashattr->size == 1 ? 2 : stroke->dashattr->size;
-        auto dashes = (float*)alloca(size * sizeof(float));
-        for (uint8_t i = 0; i < stroke->dashattr->size; ++i) {
-            auto value = stroke->dashattr->values[i](frameNo, tween, exps);
-            //FIXME: allow the zero value in the engine level.
-            dashes[i] = value < FLT_EPSILON ? 0.01f : value;
-        }
-        if (stroke->dashattr->size == 1) dashes[1] = dashes[0];
-        ctx->propagator->strokeDash(dashes, size, stroke->dashattr->offset(frameNo, tween, exps));
+        auto dashes = (float*)alloca(stroke->dashattr->size * sizeof(float));
+        for (uint8_t i = 0; i < stroke->dashattr->size; ++i) dashes[i] = stroke->dashattr->values[i](frameNo, tween, exps);
+        ctx->propagator->strokeDash(dashes, stroke->dashattr->size, stroke->dashattr->offset(frameNo, tween, exps));
     } else {
         ctx->propagator->strokeDash(nullptr, 0);
     }

src/loaders/svg/tvgSvgLoader.cpp

@@ -338,18 +338,19 @@ static void _parseDashArray(SvgLoaderData* loader, const char *str, SvgDash* das
         str = _skipComma(str);
         auto parsedValue = toFloat(str, &end);
         if (str == end) break;
-        if (parsedValue <= 0.0f) break;
+        if (parsedValue < 0.0f) {
+            dash->array.reset();
+            return;
+        }
         if (*end == '%') {
             ++end;
             //Refers to the diagonal length of the viewport.
             //https://www.w3.org/TR/SVG2/coords.html#Units
             parsedValue = (sqrtf(powf(loader->svgParse->global.w, 2) + powf(loader->svgParse->global.h, 2)) / sqrtf(2.0f)) * (parsedValue / 100.0f);
         }
-        (*dash).array.push(parsedValue);
+        dash->array.push(parsedValue);
         str = end;
     }
-    //If dash array size is 1, it means that dash and gap size are the same.
-    if ((*dash).array.count == 1) (*dash).array.push((*dash).array[0]);
 }
 
 

src/renderer/gl_engine/tvgGlTessellator.cpp

@@ -1509,7 +1509,7 @@ void Stroker::stroke(const RenderShape *rshape, const RenderPath& path)
     }
 
     auto& dash = rshape->stroke->dash;
-    if (dash.count == 0) doStroke(path);
+    if (dash.count == 0 || dash.length < DASH_PATTERN_THRESHOLD) doStroke(path);
     else doDashStroke(path, dash.pattern, dash.count, dash.offset, dash.length);
 }
 
@@ -1578,7 +1578,7 @@ void Stroker::doDashStroke(const RenderPath& path, const float *patterns, uint32
     dpath.pts.reserve(20 * path.pts.count);
 
     DashStroke dash(&dpath.cmds, &dpath.pts, patterns, patternCnt, offset, length);
-    dash.doStroke(path);
+    dash.doStroke(path, mStrokeCap != StrokeCap::Butt);
     doStroke(dpath);
 }
 
@@ -1924,7 +1924,7 @@ DashStroke::DashStroke(Array<PathCommand> *cmds, Array<Point> *pts, const float
 }
 
 
-void DashStroke::doStroke(const RenderPath& path)
+void DashStroke::doStroke(const RenderPath& path, bool drawPoint)
 {
     int32_t idx = 0;
     auto offset = mDashOffset;
@@ -1947,7 +1947,7 @@ void DashStroke::doStroke(const RenderPath& path)
     ARRAY_FOREACH(cmd, path.cmds) {
         switch (*cmd) {
             case PathCommand::Close: {
-                this->dashLineTo(mPtStart);
+                this->dashLineTo(mPtStart, drawPoint);
                 break;
             }
             case PathCommand::MoveTo: {
@@ -1961,12 +1961,12 @@ void DashStroke::doStroke(const RenderPath& path)
                 break;
             }
             case PathCommand::LineTo: {
-                this->dashLineTo(*pts);
+                this->dashLineTo(*pts, drawPoint);
                 pts++;
                 break;
             }
             case PathCommand::CubicTo: {
-                this->dashCubicTo(pts[0], pts[1], pts[2]);
+                this->dashCubicTo(pts[0], pts[1], pts[2], drawPoint);
                 pts += 3;
                 break;
             }
@@ -1976,7 +1976,7 @@ void DashStroke::doStroke(const RenderPath& path)
 }
 
 
-void DashStroke::dashLineTo(const Point& to)
+void DashStroke::dashLineTo(const Point& to, bool drawPoint)
 {
     auto len = length(mPtCur - to);
 
@@ -2007,7 +2007,18 @@ void DashStroke::dashLineTo(const Point& to)
                     }
                     this->lineTo(left.pt2);
                 }
-            } else right = curr;
+            } else {
+                if (drawPoint && !mCurOpGap) {
+                    if (drawPoint && !mCurOpGap) {
+                        if (mMove || mDashPattern[mCurrIdx] < FLOAT_EPSILON) {
+                            this->moveTo(curr.pt1);
+                            mMove = false;
+                        }
+                        this->lineTo(curr.pt1);
+                    }
+                }
+                right = curr;
+            }
             mCurrIdx = (mCurrIdx + 1) % mDashCount;
             mCurrLen = mDashPattern[mCurrIdx];
             mCurOpGap = !mCurOpGap;
@@ -2035,7 +2046,7 @@ void DashStroke::dashLineTo(const Point& to)
 }
 
 
-void DashStroke::dashCubicTo(const Point& cnt1, const Point& cnt2, const Point& end)
+void DashStroke::dashCubicTo(const Point& cnt1, const Point& cnt2, const Point& end, bool drawPoint)
 {
     Bezier cur;
     cur.start = {mPtCur.x, mPtCur.y};
@@ -2070,7 +2081,16 @@ void DashStroke::dashCubicTo(const Point& cnt1, const Point& cnt2, const Point&
                     }
                     this->cubicTo(left.ctrl1, left.ctrl2, left.end);
                 }
-            } else right = cur;
+            } else {
+                if (drawPoint && !mCurOpGap) {
+                    if (mMove || mDashPattern[mCurrIdx] < FLOAT_EPSILON) {
+                        this->moveTo(cur.start);
+                        mMove = false;
+                    }
+                    this->lineTo(cur.start);
+                }
+                right = cur;
+            }
             mCurrIdx = (mCurrIdx + 1) % mDashCount;
             mCurrLen = mDashPattern[mCurrIdx];
             mCurOpGap = !mCurOpGap;

src/renderer/gl_engine/tvgGlTessellator.h

@@ -120,11 +120,11 @@ class DashStroke
 {
 public:
     DashStroke(Array<PathCommand>* cmds, Array<Point>* pts, const float* patterns, uint32_t patternCnt, float offset, float length);
-    void doStroke(const RenderPath& path);
+    void doStroke(const RenderPath& path, bool drawPoint);
 
 private:
-    void dashLineTo(const Point& pt);
-    void dashCubicTo(const Point& pt1, const Point& pt2, const Point& pt3);
+    void dashLineTo(const Point& pt, bool drawPoint);
+    void dashCubicTo(const Point& pt1, const Point& pt2, const Point& pt3, bool drawPoint);
     void moveTo(const Point& pt);
     void lineTo(const Point& pt);
     void cubicTo(const Point& pt1, const Point& pt2, const Point& pt3);

src/renderer/sw_engine/tvgSwShape.cpp

@@ -97,7 +97,7 @@ static bool _outlineClose(SwOutline& outline)
 }
 
 
-static void _dashLineTo(SwDashStroke& dash, const Point* to, const Matrix& transform)
+static void _dashLineTo(SwDashStroke& dash, const Point* to, const Matrix& transform, bool drawPoint)
 {
     Line cur = {dash.ptCur, *to};
     auto len = cur.length();
@@ -128,6 +128,13 @@ static void _dashLineTo(SwDashStroke& dash, const Point* to, const Matrix& trans
                     _outlineLineTo(*dash.outline, &left.pt2, transform);
                 }
             } else {
+                if (drawPoint && !dash.curOpGap) {
+                    if (dash.move || dash.pattern[dash.curIdx] < FLOAT_EPSILON) {
+                        _outlineMoveTo(*dash.outline, &cur.pt1, transform);
+                        dash.move = false;
+                    }
+                    _outlineLineTo(*dash.outline, &cur.pt1, transform);
+                }
                 right = cur;
             }
             dash.curIdx = (dash.curIdx + 1) % dash.cnt;
@@ -157,7 +164,7 @@ static void _dashLineTo(SwDashStroke& dash, const Point* to, const Matrix& trans
 }
 
 
-static void _dashCubicTo(SwDashStroke& dash, const Point* ctrl1, const Point* ctrl2, const Point* to, const Matrix& transform)
+static void _dashCubicTo(SwDashStroke& dash, const Point* ctrl1, const Point* ctrl2, const Point* to, const Matrix& transform, bool drawPoint)
 {
     Bezier cur = {dash.ptCur, *ctrl1, *ctrl2, *to};
     auto len = cur.length();
@@ -189,6 +196,13 @@ static void _dashCubicTo(SwDashStroke& dash, const Point* ctrl1, const Point* ct
                     _outlineCubicTo(*dash.outline, &left.ctrl1, &left.ctrl2, &left.end, transform);
                 }
             } else {
+                if (drawPoint && !dash.curOpGap) {
+                    if (dash.move || dash.pattern[dash.curIdx] < FLOAT_EPSILON) {
+                        _outlineMoveTo(*dash.outline, &cur.start, transform);
+                        dash.move = false;
+                    }
+                    _outlineLineTo(*dash.outline, &cur.start, transform);
+                }
                 right = cur;
             }
             dash.curIdx = (dash.curIdx + 1) % dash.cnt;
@@ -218,9 +232,9 @@ static void _dashCubicTo(SwDashStroke& dash, const Point* ctrl1, const Point* ct
 }
 
 
-static void _dashClose(SwDashStroke& dash, const Matrix& transform)
+static void _dashClose(SwDashStroke& dash, const Matrix& transform, bool drawPoint)
 {
-    _dashLineTo(dash, &dash.ptStart, transform);
+    _dashLineTo(dash, &dash.ptStart, transform, drawPoint);
 }
 
 
@@ -291,10 +305,11 @@ static SwOutline* _genDashOutline(const RenderShape* rshape, const Matrix& trans
         pts++;
     }
 
+    auto drawPoint = rshape->stroke->cap != StrokeCap::Butt;
     while (--cmdCnt > 0) {
         switch (*cmds) {
             case PathCommand::Close: {
-                _dashClose(dash, transform);
+                _dashClose(dash, transform, drawPoint);
                 break;
             }
             case PathCommand::MoveTo: {
@@ -303,12 +318,12 @@ static SwOutline* _genDashOutline(const RenderShape* rshape, const Matrix& trans
                 break;
             }
             case PathCommand::LineTo: {
-                _dashLineTo(dash, pts, transform);
+                _dashLineTo(dash, pts, transform, drawPoint);
                 ++pts;
                 break;
             }
             case PathCommand::CubicTo: {
-                _dashCubicTo(dash, pts, pts + 1, pts + 2, transform);
+                _dashCubicTo(dash, pts, pts + 1, pts + 2, transform, drawPoint);
                 pts += 3;
                 break;
             }
@@ -508,7 +523,17 @@ bool shapeGenStrokeRle(SwShape* shape, const RenderShape* rshape, const Matrix&
     auto ret = true;
 
     //Dash style with/without trimming
-    if (rshape->stroke->dash.count > 0) {
+    if (rshape->stroke->dash.count > 0 && rshape->stroke->dash.length > DASH_PATTERN_THRESHOLD) {
+        //check if the length of the drawn dashes is negligibly small => if yes, then it's a valid shape without a stroke
+        if (rshape->stroke->cap == StrokeCap::Butt) {
+            auto len = 0.0f;
+            for (uint32_t i = 0; i < rshape->stroke->dash.count; i += 2) len += rshape->stroke->dash.pattern[i];
+            if (len < DASH_PATTERN_THRESHOLD) {
+                ret = true;
+                goto clear;
+            }
+        }
+
         shapeOutline = _genDashOutline(rshape, transform, mpool, tid, rshape->trimpath());
         if (!shapeOutline) return false;
         dashStroking = true;

src/renderer/tvgShape.h

@@ -290,7 +290,7 @@ struct ShapeImpl : Shape
 
     Result strokeDash(const float* pattern, uint32_t cnt, float offset)
     {
-        if ((cnt == 1) || (!pattern && cnt > 0) || (pattern && cnt == 0)) return Result::InvalidArguments;
+        if ((!pattern && cnt > 0) || (pattern && cnt == 0)) return Result::InvalidArguments;
         if (!rs.stroke) rs.stroke = new RenderStroke;
         //Reset dash
         auto& dash = rs.stroke->dash;
@@ -302,11 +302,7 @@ struct ShapeImpl : Shape
             if (!dash.pattern) dash.pattern = tvg::malloc<float*>(sizeof(float) * cnt);
             dash.length = 0.0f;
             for (uint32_t i = 0; i < cnt; ++i) {
-                if (pattern[i] < DASH_PATTERN_THRESHOLD) {
-                    dash.count = 0;
-                    return Result::InvalidArguments;
-                }
-                dash.pattern[i] = pattern[i];
+                dash.pattern[i] = pattern[i] < 0.0f ? 0.0f : pattern[i];
                 dash.length += dash.pattern[i];
             }
         }

src/renderer/wg_engine/tvgWgGeometry.h

@@ -359,7 +359,7 @@ struct WgIndexedVertexBuffer
         dashed->reset(scale);
         auto& dash = rstroke->dash;
 
-        if (buff.count < 2 || tvg::zero(dash.length)) return;
+        if (buff.count < 2) return;
 
         uint32_t index = 0;
         auto total = dash.pattern[index];
@@ -372,12 +372,14 @@ struct WgIndexedVertexBuffer
         auto gap = false;
 
         // scip dashes by offset
-        while(total <= dashOffset) {
-            index = (index + 1) % dash.count;
-            total += dash.pattern[index];
-            gap = !gap;
+        if (dashOffset > 0.0f) {
+            while(total <= dashOffset) {
+                index = (index + 1) % dash.count;
+                total += dash.pattern[index];
+                gap = !gap;
+            }
+            total -= dashOffset;
         }
-        total -= dashOffset;
 
         // iterate by polyline points
         for (uint32_t i = 0; i < buff.count - 1; i++) {
@@ -466,7 +468,10 @@ struct WgIndexedVertexBuffer
 
     void appendSquare(Point v0, Point v1, float dist, float halfWidth)
     {
-        if(tvg::zero(dist)) return;
+        if(tvg::zero(dist)) {
+            appendQuad(v1 + Point{-halfWidth, -halfWidth}, v1 + Point{-halfWidth, halfWidth}, v1 + Point{halfWidth, -halfWidth}, v1 + Point{halfWidth, halfWidth});
+            return;
+        }
         Point sub = v1 - v0;
         Point offset = sub / dist * halfWidth;
         Point nrm = {+offset.y, -offset.x};

src/renderer/wg_engine/tvgWgRenderData.cpp

@@ -394,7 +394,7 @@ void WgRenderDataShape::proceedStrokes(WgContext& context, const RenderStroke* r
 {
     assert(rstroke);
     auto strokesGenerator = pool->reqIndexedVertexBuffer(buff.scale);
-    if (rstroke->dash.count == 0) strokesGenerator->appendStrokes(buff, rstroke);
+    if (rstroke->dash.count == 0 || rstroke->dash.length < DASH_PATTERN_THRESHOLD) strokesGenerator->appendStrokes(buff, rstroke);
     else strokesGenerator->appendStrokesDashed(buff, rstroke);
 
     appendStroke(context, *strokesGenerator);

test/testShape.cpp

@@ -157,21 +157,30 @@ TEST_CASE("Stroking", "[tvgShape]")
     REQUIRE(shape->strokeFill(nullptr, nullptr, nullptr, nullptr) == Result::Success);
 
     //Stroke Dash
-    float dashPattern[3] = {0, 1.5f, 2.22f};
-    REQUIRE(shape->strokeDash(dashPattern, 3) == Result::InvalidArguments);
+    REQUIRE(shape->strokeDash(nullptr, 3) == Result::InvalidArguments);
 
-    float dashPattern2[3] = {1.0f, 1.5f, 2.22f};
-    REQUIRE(shape->strokeDash(dashPattern2, 3) == Result::Success);
-    REQUIRE(shape->strokeDash(dashPattern2, 3, 4.5) == Result::Success);
+    float dashPattern0[3] = {-10.0f, 1.5f, 2.22f};
+    REQUIRE(shape->strokeDash(dashPattern0, 0) == Result::InvalidArguments);
+    REQUIRE(shape->strokeDash(dashPattern0, 3) == Result::Success);
 
-    const float* dashPattern3;
+    float dashPattern1[2] = {0.0f, 0.0f};
+    REQUIRE(shape->strokeDash(dashPattern1, 2) == Result::Success);
+
+    float dashPattern2[1] = {10.0f};
+    REQUIRE(shape->strokeDash(dashPattern2, 1) == Result::Success);
+
+    float dashPattern3[3] = {1.0f, 1.5f, 2.22f};
+    REQUIRE(shape->strokeDash(dashPattern3, 3) == Result::Success);
+    REQUIRE(shape->strokeDash(dashPattern3, 3, 4.5) == Result::Success);
+
+    const float* dashPattern4;
     float offset;
     REQUIRE(shape->strokeDash(nullptr) == 3);
-    REQUIRE(shape->strokeDash(&dashPattern3) == 3);
-    REQUIRE(shape->strokeDash(&dashPattern3, &offset) == 3);
-    REQUIRE(dashPattern3[0] == 1.0f);
-    REQUIRE(dashPattern3[1] == 1.5f);
-    REQUIRE(dashPattern3[2] == 2.22f);
+    REQUIRE(shape->strokeDash(&dashPattern4) == 3);
+    REQUIRE(shape->strokeDash(&dashPattern4, &offset) == 3);
+    REQUIRE(dashPattern4[0] == 1.0f);
+    REQUIRE(dashPattern4[1] == 1.5f);
+    REQUIRE(dashPattern4[2] == 2.22f);
     REQUIRE(offset == 4.5f);
 
     REQUIRE(shape->strokeDash(nullptr, 0) == Result::Success);