From 03bbfd3183c64675d62df077ac2c9370e493b105 Mon Sep 17 00:00:00 2001
From: Mira Grudzinska <mira@lottiefiles.com>
Date: Tue, 1 Oct 2024 15:17:50 +0200
Subject: [PATCH] sw_engine: ignore small cubics

During the stroke's outline calculation, the function
handling small cubics set all angles to zero. When
the cubic was small but not zero, this resulted in
incorrect outlines. Now such curves are ignored.

Co-Authored-By: Hermet Park <hermet@lottiefiles.com>

Issue: https://github.com/thorvg/thorvg/issues/2776
Issue: https://github.com/thorvg/thorvg/issues/2712
---
 src/renderer/sw_engine/tvgSwCommon.h   |  2 +-
 src/renderer/sw_engine/tvgSwMath.cpp   |  8 ++++----
 src/renderer/sw_engine/tvgSwStroke.cpp | 12 +++++++++++-
 3 files changed, 16 insertions(+), 6 deletions(-)

diff --git a/src/renderer/sw_engine/tvgSwCommon.h b/src/renderer/sw_engine/tvgSwCommon.h
index 9df20bb5..f8491bbf 100644
--- a/src/renderer/sw_engine/tvgSwCommon.h
+++ b/src/renderer/sw_engine/tvgSwCommon.h
@@ -490,7 +490,7 @@ SwFixed mathSin(SwFixed angle);
 void mathSplitCubic(SwPoint* base);
 SwFixed mathDiff(SwFixed angle1, SwFixed angle2);
 SwFixed mathLength(const SwPoint& pt);
-bool mathSmallCubic(const SwPoint* base, SwFixed& angleIn, SwFixed& angleMid, SwFixed& angleOut);
+int mathCubicAngle(const SwPoint* base, SwFixed& angleIn, SwFixed& angleMid, SwFixed& angleOut);
 SwFixed mathMean(SwFixed angle1, SwFixed angle2);
 SwPoint mathTransform(const Point* to, const Matrix& transform);
 bool mathUpdateOutlineBBox(const SwOutline* outline, const SwBBox& clipRegion, SwBBox& renderRegion, bool fastTrack);
diff --git a/src/renderer/sw_engine/tvgSwMath.cpp b/src/renderer/sw_engine/tvgSwMath.cpp
index 1093edd6..0b85d890 100644
--- a/src/renderer/sw_engine/tvgSwMath.cpp
+++ b/src/renderer/sw_engine/tvgSwMath.cpp
@@ -44,7 +44,7 @@ SwFixed mathMean(SwFixed angle1, SwFixed angle2)
 }
 
 
-bool mathSmallCubic(const SwPoint* base, SwFixed& angleIn, SwFixed& angleMid, SwFixed& angleOut)
+int mathCubicAngle(const SwPoint* base, SwFixed& angleIn, SwFixed& angleMid, SwFixed& angleOut)
 {
     auto d1 = base[2] - base[3];
     auto d2 = base[1] - base[2];
@@ -54,7 +54,7 @@ bool mathSmallCubic(const SwPoint* base, SwFixed& angleIn, SwFixed& angleMid, Sw
         if (d2.small()) {
             if (d3.small()) {
                 angleIn = angleMid = angleOut = 0;
-                return true;
+                return -1;  //ignoreable
             } else {
                 angleIn = angleMid = angleOut = mathAtan(d3);
             }
@@ -90,8 +90,8 @@ bool mathSmallCubic(const SwPoint* base, SwFixed& angleIn, SwFixed& angleMid, Sw
     auto theta1 = abs(mathDiff(angleIn, angleMid));
     auto theta2 = abs(mathDiff(angleMid, angleOut));
 
-    if ((theta1 < (SW_ANGLE_PI / 8)) && (theta2 < (SW_ANGLE_PI / 8))) return true;
-    return false;
+    if ((theta1 < (SW_ANGLE_PI / 8)) && (theta2 < (SW_ANGLE_PI / 8))) return 0; //small size
+    return 1;
 }
 
 
diff --git a/src/renderer/sw_engine/tvgSwStroke.cpp b/src/renderer/sw_engine/tvgSwStroke.cpp
index 9a27f03d..e195f72a 100644
--- a/src/renderer/sw_engine/tvgSwStroke.cpp
+++ b/src/renderer/sw_engine/tvgSwStroke.cpp
@@ -441,13 +441,23 @@ static void _cubicTo(SwStroke& stroke, const SwPoint& ctrl1, const SwPoint& ctrl
         //initialize with current direction
         angleIn = angleOut = angleMid = stroke.angleIn;
 
-        if (arc < limit && !mathSmallCubic(arc, angleIn, angleMid, angleOut)) {
+        auto valid = mathCubicAngle(arc, angleIn, angleMid, angleOut);
+
+        //valid size
+        if (valid > 0 && arc < limit) {
             if (stroke.firstPt) stroke.angleIn = angleIn;
             mathSplitCubic(arc);
             arc += 3;
             continue;
         }
 
+        //ignoreable size
+        if (valid < 0 && arc == bezStack) {
+            stroke.center = to;
+            return;
+        }
+
+        //small size
         if (firstArc) {
             firstArc = false;
             //process corner if necessary