From a3fd4a6e9bba6b375c7a00abe902a88ef31dfbe0 Mon Sep 17 00:00:00 2001
From: themancalledjakob <jakob@jrkb.land>
Date: Sat, 27 May 2023 10:31:45 +0200
Subject: [PATCH] flip contour if counter-clockwise

---
 src/gpufont/font.hpp | 35 +++++++++++++++++++++++++++++++++--
 1 file changed, 33 insertions(+), 2 deletions(-)

diff --git a/src/gpufont/font.hpp b/src/gpufont/font.hpp
index 49f0348..fa2bb70 100644
--- a/src/gpufont/font.hpp
+++ b/src/gpufont/font.hpp
@@ -906,7 +906,11 @@ class Font {
         // This function takes a single contour (defined by firstIndex and
         // lastIndex, both inclusive) from outline and converts it into individual
         // quadratic bezier curves, which are added to the curves vector.
-        void convertContour(std::vector <BufferCurve> & curves, const FT_Outline * outline, short firstIndex, short lastIndex, float emSize){
+        void convertContour(std::vector <BufferCurve> & all_curves, const FT_Outline * outline, short firstIndex, short lastIndex, float emSize){
+            // we might have to flip the direction
+            // so let's buffer our buffercurves in a buffer curves of buffercurves
+            std::vector <BufferCurve> curves;
+
             // See https://freetype.org/freetype2/docs/glyphs/glyphs-6.html
             // for a detailed description of the outline format.
             //
@@ -989,7 +993,21 @@ class Font {
                                     return 0.5f * (a + b);
                                 };
 
-            auto makeCurve = [](const glm::vec2 & p0, const glm::vec2 & p1, const glm::vec2 & p2){
+
+            // Get Direction of a point pair.
+            // Notice that we can ignore the middle point.
+            auto getDirection = [](const glm::vec2 & p0, const glm::vec2 & p1){
+                                    return (p1.x - p0.x) * (p1.y + p0.y);
+                                };
+
+            // keep track of collected direction
+            float direction = 0;
+
+            // We will inject getDirection in makeCurve,
+            // so anytime the curve is made it updates the direction.
+            // This is less error prone than calling it separately.
+            // wisdom: Any error you cannot make, you will not make. :)
+            auto makeCurve = [&direction, getDirection](const glm::vec2 & p0, const glm::vec2 & p1, const glm::vec2 & p2){
                                  BufferCurve result;
                                  result.x0 = p0.x;
                                  result.y0 = p0.y;
@@ -997,6 +1015,7 @@ class Font {
                                  result.y1 = p1.y;
                                  result.x2 = p2.x;
                                  result.y2 = p2.y;
+                                 direction += getDirection(p0, p2);
                                  return result;
                              };
 
@@ -1086,6 +1105,18 @@ class Font {
             }else{
                 curves.push_back(makeCurve(start, previous, first));
             }
+            if(direction < 0){
+                for(BufferCurve & curve : curves){
+                    float tmp_x = curve.x0;
+                    float tmp_y = curve.y0;
+                    curve.x0 = curve.x2;
+                    curve.y0 = curve.y2;
+                    curve.x2 = tmp_x;
+                    curve.y2 = tmp_y;
+                }
+                std::reverse(curves.begin(), curves.end());
+            }
+            all_curves.insert(all_curves.end(), curves.begin(), curves.end());
         }