Fix leading zero being displayed (#190)

* Rewrote the digit drawing algorithm

* Ensure that digits are rendered only when in 1s place, highlighted, or meets min digit value
Otherwise, blanked.

* Signed power value

opendps/uui_number.c

@@ -234,51 +234,56 @@ static void number_draw(ui_item_t *_item)
         xpos -= number_draw_width(_item);
 
     /** Start printing from left to right */
+    for (uint8_t place = item->num_digits; place > 0; place--) {
+        /* Example value of 1000 with 5,2:
+            01000 . 00  num_digits = 5, num_decimals = 2
+            54321       values place
+            65432 . 10  cur_digit
+        */
 
-    /** Digits before the decimal point */
-    for (uint32_t i = item->num_digits - 1; i < item->num_digits; --i) {
+        // current digit
+        cur_digit = place + item->num_decimals - 1;
+
+        // this place value (1 = 1, 2 = 10, 3 = 100, etc., for si_prefix = 0)
+        int32_t power = my_pow(10, (item->si_prefix * -1) + (place - 1));
+
+        uint8_t digit = (item->value / power) % 10;
+
+        // digit selected
         bool highlight = _item->has_focus && item->cur_digit == cur_digit;
-        uint8_t digit = item->value / my_pow(10, (item->si_prefix * -1) + i) % 10;
 
-        if (!digit /** If current digit is a 0 */
-            && !_item->has_focus /** and its not in focus (selected) */
-            && cur_digit != item->num_decimals /** to prevent 0.123 becoming .123 */
-            && my_pow(10, cur_digit) > (uint32_t) item->value) /** to prevent 4023 becoming 4 23 */
-        {
-            /** To prevent from printing 00.123 */
-            /** Black out any 0 that has previously been printed */
-            if (spacing > 1)
-            {
-                tft_fill(xpos, _item->y, digit_w, h, BLACK);
-                tft_rect(xpos-1, _item->y-1, digit_w+1, h+1, BLACK); /** Remove any potential frame highlight */
+        // Draw background either black, or a highlighted box
+        if (spacing > 1) {
+            if (highlight) {
+                tft_rect(xpos-1, _item->y-1, digit_w+1, h+1, WHITE);
+            } else {
+                tft_rect(xpos-1, _item->y-1, digit_w+1, h+1, BLACK);
             }
-            else
-                tft_fill(xpos, _item->y, digit_w, h, BLACK); /** Black out any 0 that has previously been printed */
         }
-        else
-        {
-            if (spacing > 1) /** Dont frame tiny fonts */
-            {
-                if (highlight) /** Draw an extra pixel wide border around the highlighted item */
-                    tft_rect(xpos-1, _item->y-1, digit_w+1, h+1, WHITE);
-                else
-                    tft_rect(xpos-1, _item->y-1, digit_w+1, h+1, BLACK);
-            }
+
+        // Draw the digit, Only if:
+        //   value >= this place's min value (ie. digit's power)
+        //   in one's place (ensuring 0.xxx has leading 0)
+        //   or item has focus (ensures all digits are drawn when focused)
+        if (item->value >= power || place == 1 || _item->has_focus) {
+            // ASCII '0' plus digit value for digit ascii offset
             tft_putch(item->font_size, '0' + digit, xpos, _item->y, digit_w, h, color, highlight);
+        } else {
+            tft_fill(xpos, _item->y, digit_w, h, BLACK);
         }
 
-        cur_digit--;
+        // next digit position
         xpos += digit_w + spacing;
     }
 
-    /** Draw the decimal point if there is decimal places */
-    if (item->num_decimals)
-    {
+    /** Draw the decimal point if there are decimal places */
+    if (item->num_decimals) {
         tft_putch(item->font_size, '.', xpos, _item->y, dot_width, h, color, false);
         xpos += dot_width + spacing;
     }
 
     /** Digits after the decimal point */
+    cur_digit = item->num_decimals - 1;
     for (uint32_t i = 0; i < item->num_decimals; ++i) {
         bool highlight = _item->has_focus && item->cur_digit == cur_digit;
         uint8_t digit = item->value / my_pow(10, (item->si_prefix * -1) -1 - i) % 10;