captouch: linearized bottom petal pos a bit

components/flow3r_bsp/flow3r_bsp_ad7147.c

@@ -1401,6 +1401,16 @@ static inline void pos_calc_bot(int index, int mode, int *rad, int *raw_sum,
         int rad_calc = tip - base;
         rad_calc *= petal_pos_gain[index];
         rad_calc /= ((tip + base) >> 2) + 1;
+
+        rad_calc = 16384 - rad_calc;
+
+        int rad_calc_gain = rad_calc > 0 ? rad_calc : 0;
+        rad_calc_gain = (rad_calc_gain + 32768) >> 5;
+        rad_calc_gain = (rad_calc_gain * rad_calc_gain) >> 12;
+        rad_calc = (rad_calc * rad_calc_gain) >> 10;
+
+        rad_calc = 16384 - rad_calc;
+
         *rad = rad_calc;
     } else {
         *rad = 0;
@@ -1435,9 +1445,20 @@ static inline void pos_calc_top2(int index, int mode, int *rad, int *phi,
     }
 }
 
-static void pos_calc_bot2(int index, int mode, int *rad, int *raw_sum,
-                          uint16_t *raw_petal) {
-    pos_calc_bot(index, mode, rad, raw_sum, raw_petal);
+static inline void pos_calc_bot2(int index, int mode, int *rad, int *raw_sum,
+                                 uint16_t *raw_petal) {
+    int32_t tip = raw_petal[petal_pad_tip];
+    int32_t base = raw_petal[petal_pad_base];
+    *raw_sum = base + tip;
+    if (mode > 1) {
+        base += ((base * 3) >> 2);  // tiny gain correction
+        int rad_calc = tip - base;
+        rad_calc *= petal_pos_gain[index];
+        rad_calc /= ((tip + base) >> 2) + 1;
+        *rad = rad_calc;
+    } else {
+        *rad = 0;
+    }
 }
 #endif