# HG changeset patch
# User Teemu Piippo <teemu.s.piippo@gmail.com>
# Date 1655903548 -10800
# Node ID 07ad61423c3c1efe99c314f14c7bb1fbcc0b8ff4
# Parent  86a35ce38773807fe842c7afb4f4ea703284920a
fix cylinders being possibly rendered inside out

diff -r 86a35ce38773 -r 07ad61423c3c src/circularprimitive.h
--- a/src/circularprimitive.h	Mon Jun 20 23:05:27 2022 +0300
+++ b/src/circularprimitive.h	Wed Jun 22 16:12:28 2022 +0300
@@ -12,6 +12,7 @@
 		return glm::vec3{circ.transformation * glm::vec4{p.x, y, p.y, 1}};
 	};
 	const glm::vec3 origin = xform({0, 0}, 0);
+	const bool invertedMatrix = (glm::determinant(circ.transformation) < 0) != circ.inverted;
 	switch(circ.type) {
 	case CircularPrimitive::Circle:
 		ldraw::circle(circ.fraction.segments, circ.fraction.divisions, [&]
@@ -28,7 +29,11 @@
 	case CircularPrimitive::Cylinder:
 		ldraw::circle(circ.fraction.segments, circ.fraction.divisions, [&]
 		(const glm::vec2&, const glm::vec2& p1, const glm::vec2& p2){
-			fn(quadrilateral(xform(p1, 1), xform(p2, 1), xform(p2, 0), xform(p1, 0)));
+			Colored<Quadrilateral> quad = quadrilateral(xform(p1, 1), xform(p2, 1), xform(p2, 0), xform(p1, 0));
+			if (invertedMatrix) {
+				std::swap(quad.p2, quad.p4);
+			}
+			fn(quad);
 		});
 		break;
 	case CircularPrimitive::CylinderOpen: