🐛 Prevent arc segments > configured size

Fixing #22571

Marlin/src/gcode/motion/G2_G3.cpp

@@ -147,8 +147,8 @@ void plan_arc(
 
  const feedRate_t scaled_fr_mm_s = MMS_SCALED(feedrate_mm_s);
 
- // Start with a nominal segment length
- float seg_length = (
+ // Determine the segment length based on settings
+ const float seg_length = (
  #ifdef ARC_SEGMENTS_PER_R
  constrain(MM_PER_ARC_SEGMENT * radius, MM_PER_ARC_SEGMENT, ARC_SEGMENTS_PER_R)
  #elif ARC_SEGMENTS_PER_SEC
@@ -157,10 +157,14 @@ void plan_arc(
  MM_PER_ARC_SEGMENT
  #endif
  );
- // Divide total travel by nominal segment length
+ // Divide total travel by segment length
  uint16_t segments = FLOOR(mm_of_travel / seg_length);
  NOLESS(segments, min_segments); // At least some segments
- seg_length = mm_of_travel / segments;
+
+ // Are the segments now too few to reach the destination?
+ const float segmented_length = seg_length * segments;
+ const bool tooshort = segmented_length < mm_of_travel - 0.1f;
+ const float proportion = tooshort ? segmented_length / mm_of_travel : 1.0f;
 
  /**
  * Vector rotation by transformation matrix: r is the original vector, r_T is the rotated vector,
@@ -190,26 +194,29 @@ void plan_arc(
  */
  // Vector rotation matrix values
  xyze_pos_t raw;
- const float theta_per_segment = angular_travel / segments,
+ const float theta_per_segment = proportion * angular_travel / segments,
  sq_theta_per_segment = sq(theta_per_segment),
  sin_T = theta_per_segment - sq_theta_per_segment * theta_per_segment / 6,
  cos_T = 1 - 0.5f * sq_theta_per_segment; // Small angle approximation
 
  #if HAS_Z_AXIS && DISABLED(AUTO_BED_LEVELING_UBL)
- const float linear_per_segment = linear_travel / segments;
+ const float linear_per_segment = proportion * linear_travel / segments;
  #endif
  #if HAS_EXTRUDERS
- const float extruder_per_segment = extruder_travel / segments;
+ const float extruder_per_segment = proportion * extruder_travel / segments;
  #endif
 
+ // For shortened segments, run all but the remainder in the loop
+ if (tooshort) segments++;
+
  // Initialize the linear axis
  TERN_(HAS_Z_AXIS, raw[l_axis] = current_position[l_axis]);
 
  // Initialize the extruder axis
  TERN_(HAS_EXTRUDERS, raw.e = current_position.e);
 
  #if ENABLED(SCARA_FEEDRATE_SCALING)
- const float inv_duration = scaled_fr_mm_s / seg_length;
+ const float inv_duration = scaled_fr_mm_s * segments / mm_of_travel;
  #endif
 
  millis_t next_idle_ms = millis() + 200UL;
@@ -221,8 +228,9 @@ void plan_arc(
  for (uint16_t i = 1; i < segments; i++) { // Iterate (segments-1) times
 
  thermalManager.manage_heater();
- if (ELAPSED(millis(), next_idle_ms)) {
- next_idle_ms = millis() + 200UL;
+ const millis_t ms = millis();
+ if (ELAPSED(ms, next_idle_ms)) {
+ next_idle_ms = ms + 200UL;
  idle();
  }