🐛 Limit FTM reset-on-threshold E pos to maintain precision (#28192)

Marlin/src/module/ft_motion.cpp

@@ -349,6 +349,7 @@ bool FTMotion::plan_next_block() {
       if (current_block->is_sync_pos()) stepper._set_position(current_block->position);
       continue;
     }
+    ensure_float_precision();
 
     #if ENABLED(POWER_LOSS_RECOVERY)
       recovery.info.sdpos = current_block->sdpos;
@@ -400,6 +401,39 @@ bool FTMotion::plan_next_block() {
   }
 }
 
+/**
+ * Ensure extruder position stays within floating point precision bounds.
+ * Float32 numbers have 23 bits of precision, so the minimum increment ("resolution") around a value x is:
+ * resolution = 2^(floor(log2(|x|)) - 23)
+ * By resetting at ±1'000mm (1 meter), we get a minimum resolution of ~ 0.00006mm, enough for smoothing to work well.
+ */
+void FTMotion::ensure_float_precision() {
+  constexpr float FTM_POSITION_WRAP_THRESHOLD = 1'000.0f;  // (mm) Reset when position exceeds this to prevent floating point precision loss
+  #if HAS_EXTRUDERS
+    if (fabs(endPos_prevBlock.E) >= FTM_POSITION_WRAP_THRESHOLD) {
+      const float offset = -endPos_prevBlock.E;
+      endPos_prevBlock.E += offset;
+
+      // Offset extruder shaping buffer
+      #if ALL(HAS_FTM_SHAPING, FTM_SHAPER_E)
+        for (uint32_t i = 0; i < FTM_ZMAX; ++i) shaping.E.d_zi[i] += offset;
+      #endif
+
+      // Offset extruder smoothing buffer
+      #if ENABLED(FTM_SMOOTHING)
+        for (uint8_t i = 0; i < FTM_SMOOTHING_ORDER; ++i) smoothing.E.smoothing_pass[i] += offset;
+      #endif
+
+      // Offset linear advance previous position
+      prev_traj_e += offset;
+
+      // Offset stepper current position
+      const int64_t delta_steps_q48_16 = offset * planner.settings.axis_steps_per_mm[block_extruder_axis] * (1ULL << 16);
+      stepping.curr_steps_q48_16.E += delta_steps_q48_16;
+    };
+  #endif
+}
+
 xyze_float_t FTMotion::calc_traj_point(const float dist) {
   xyze_float_t traj_coords;
   #define _SET_TRAJ(q) traj_coords.q = startPos.q + ratio.q * dist;

Marlin/src/module/ft_motion.h

@@ -280,6 +280,7 @@ class FTMotion {
     static void fill_stepper_plan_buffer();
     static xyze_float_t calc_traj_point(const float dist);
     static bool plan_next_block();
+    static void ensure_float_precision();
 
 }; // class FTMotion
 

Marlin/src/module/ft_motion/stepping.h

@@ -233,9 +233,11 @@ typedef struct Stepping {
   FORCE_INLINE bool is_busy() {
     return !(is_empty() && ticks_left_in_frame_fp == 0);
   }
+
   FORCE_INLINE bool is_empty() {
     return stepper_plan_head == stepper_plan_tail;
   }
+
   FORCE_INLINE bool is_full() {
     return ((stepper_plan_head + 1) & FTM_BUFFER_MASK) == stepper_plan_tail;
   }