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4.15.5 Field Display Attributes

As you have seen, in the above example, display attributes for the fields can be set with set-field-fore! and set-field-back!. These functions set foreground and background attributes of the fields. You can also specify a pad character that will be filled in the unfilled portion of the field. The pad character is set with a call to set-field-pad!. Default pad value is space. The functions field-fore , field-back, and field-pad can be used to query the present foreground background attributes and pad character for the field.

Though the functions seem quite simple, using colors with set-field-fore! may be frustrating in the beginning. Let me first explain about foreground and background attributes of a field. The foreground attribute is associated with the character. That means a character in the field is printed with the attribute you have set with set-field-fore!. Background attribute is the attribute used to fill background of field, whether any character is there or not. So what about colors? Since colors are always defined in pairs, what is the right way to display colored fields? Here’s an example clarifying color attributes.


(use-modules (srfi srfi-1)
             (ncurses curses)
             (ncurses form))

;; Initialize curses
(define stdscr (initscr))
(keypad! stdscr #t)

;; Initialize the color pairs

;; Initialize the fields
(define field (list
               (new-field 1 10 4 18 0 0)
               (new-field 1 10 6 18 0 0)))

;; Set field options
(set-field-fore! (first field) (color-pair 1))
(set-field-back! (first field) (color-pair 2))
(field-opts-off! (first field) O_AUTOSKIP)

(set-field-back! (second field) A_UNDERLINE)
(field-opts-off! (second field) O_AUTOSKIP)

;; Create the new form and post it
(define my-form (new-form field))
(post-form my-form)
(refresh stdscr)

(addstr stdscr "Value 1:" #:y 4 #:x 10)
(addstr stdscr "Value 2:" #:y 6 #:x 10)
(refresh stdscr)

;; Loop through to get user requests
(let loop ((ch (getch stdscr)))
  (if (not (eqv? ch (key-f 1)))
       ((eqv? ch KEY_DOWN)
          ;; Go to the end of the next field
          (form-driver my-form REQ_NEXT_FIELD)
          (form-driver my-form REQ_END_LINE)
          (loop (getch stdscr))))
       ((eqv? ch KEY_UP)
          ;; Go to the end of the previous field
          (form-driver my-form REQ_PREV_FIELD)
          (form-driver my-form REQ_END_LINE)
          (loop (getch stdscr))))
          ;; Print any normal character
          (form-driver my-form ch)
          (loop (getch stdscr)))))))

;; Unpost the form
(unpost-form my-form)


Play with the color pairs and try to understand the foreground and background attributes. Color pair 1 is used for the character that have been typed into the form, and color pair 2 is used for the empty spaces in the form.

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