From f2708d81eff44378af10936b0c5e1541aec6d868 Mon Sep 17 00:00:00 2001
From: gb0101010101 <7369439+gb0101010101@users.noreply.github.com>
Date: Wed, 13 May 2020 20:26:04 -0700
Subject: [PATCH] Support using radius R in G2 and G3 commands.

---
 File/gcodeFile.py | 30 ++++++++++++++++++++++++++++++
 1 file changed, 30 insertions(+)

diff --git a/File/gcodeFile.py b/File/gcodeFile.py
index b027b21c..a2fea6a5 100644
--- a/File/gcodeFile.py
+++ b/File/gcodeFile.py
@@ -412,6 +412,36 @@ def drawArc(self, gCodeLine, command):
             centerX = self.xPosition + iTarget
             centerY = self.yPosition + jTarget
 
+            # If radius R is provided in gcode then work out centerpoint ignoring I J.
+            r = re.search("R(?=.)(([ ]*)?[+-]?([0-9]*)(\.([0-9]+))?)", gCodeLine)
+            if r:
+                x1 = self.xPosition
+                x2 = xTarget
+                y1 = self.yPosition
+                y2 = yTarget
+
+                radius = float(r.groups()[0]) * self.canvasScaleFactor
+                # e: clockwise -1, counterclockwise 1
+                e = 1
+                if ((int(command[1:]) == 2)):
+                    e = -1
+                # X and Y differences
+                dx = x2 - x1
+                dy = y2 - y1
+                # Linear distance between the points.
+                d = math.hypot(dx, dy)
+                # Distance to the arc pivot-point.
+                h = math.sqrt(math.pow(radius, 2) - math.pow(d * 0.5, 2))
+                # Point between the two points.
+                mx = (x1 + x2) * 0.5
+                my = (y1 + y2) * 0.5
+                # Slope of the perpendicular bisector.
+                sx = -dy / d
+                sy = dx / d
+                # Pivot-point of the arc.
+                centerX = mx + e * h * sx
+                centerY = my + e * h * sy
+
             angle1 = math.atan2(self.yPosition - centerY, self.xPosition - centerX)
             angle2 = math.atan2(yTarget - centerY, xTarget - centerX)