Arc segment radius scaling (#16551)

Marlin/Configuration_adv.h

@@ -1570,6 +1570,7 @@
 #define ARC_SUPPORT                 // Disable this feature to save ~3226 bytes
 #if ENABLED(ARC_SUPPORT)
   #define MM_PER_ARC_SEGMENT      1 // (mm) Length (or minimum length) of each arc segment
+  //#define ARC_SEGMENTS_PER_R    1 // Max segment length, MM_PER = Min
   #define MIN_ARC_SEGMENTS       24 // Minimum number of segments in a complete circle
   //#define ARC_SEGMENTS_PER_SEC 50 // Use feedrate to choose segment length (with MM_PER_ARC_SEGMENT as the minimum)
   #define N_ARC_CORRECTION       25 // Number of interpolated segments between corrections

Marlin/src/gcode/motion/G2_G3.cpp

@@ -105,7 +105,10 @@ void plan_arc(
 
   const feedRate_t scaled_fr_mm_s = MMS_SCALED(feedrate_mm_s);
 
-  #ifdef ARC_SEGMENTS_PER_SEC
+  #ifdef ARC_SEGMENTS_PER_R
+    float seg_length = MM_PER_ARC_SEGMENT * radius;
+    LIMIT(seg_length, MM_PER_ARC_SEGMENT, ARC_SEGMENTS_PER_R);
+  #elif ARC_SEGMENTS_PER_SEC
     float seg_length = scaled_fr_mm_s * RECIPROCAL(ARC_SEGMENTS_PER_SEC);
     NOLESS(seg_length, MM_PER_ARC_SEGMENT);
   #else