Draw regular polygons with an inner circle radius

TikZ determines the size of a regular polygon by the radius of a circle
inscribed inside the shape, touching the middle of each edge, not a
circle outside the sahep, touching each vertex.

1 files changed, 7 insertions, 1 deletions

diff --git a/tikzit/src/common/RegularPolyShape.m b/tikzit/src/common/RegularPolyShape.m
index b9acdf3..3555115 100644
--- a/tikzit/src/common/RegularPolyShape.m
+++ b/tikzit/src/common/RegularPolyShape.m
@@ -34,7 +34,10 @@
 	if (self == nil)
 		return nil;
 
-	float radius = 0.25f;
+	// TikZ draws regular polygons using a radius inscribed
+	// _inside_ the shape (touching middles of edges), not
+	// outside (touching points)
+	const float innerRadius = 0.2f;
 
 	NSMutableArray *nodes = [NSMutableArray arrayWithCapacity:sides];
 	NSMutableArray *edges = [NSMutableArray arrayWithCapacity:sides];
@@ -42,6 +45,9 @@
 	float dtheta = (M_PI * 2.0f) / ((float)sides);
 	float theta = (dtheta/2.0f) - (M_PI / 2.0f);
 	theta += degreesToRadians(rotation);
+	// radius of the outer circle
+	float radius = ABS(innerRadius / cos(dtheta));
+
 	for (int i = 0; i < sides; ++i) {
 		NSPoint p;
 		p.x = radius * cos(theta);