RE: Negative positions in frame parameters

["Drew Adams" <drew.adams@oracle.com>]

FWIW, I've been using the following functions forever, to make life simpler when
trying to deal with the different possible representations that Emacs functions
might return.

I use this, for example, to move frames around incrementally. (To increment a
value it needs to be in numeric form.)

The functions are also here, in case mail wraparound makes them difficult to
read:
http://www.emacswiki.org/emacs/frame-fns.el

----

(defun frame-geom-value-numeric (type value &optional frame)
  "Return equivalent geometry value for FRAME in numeric terms.
A geometry value equivalent to VALUE for FRAME is returned,
where the value is numeric, not a consp.
TYPE is the car of the original geometry spec (TYPE . VALUE).
   It is `top' or `left', depending on which edge VALUE is related to.
VALUE is the cdr of a frame geometry spec: (left/top . VALUE).
If VALUE is a consp, then it is converted to a numeric value, perhaps
   relative to the opposite frame edge from that in the original spec.
FRAME defaults to the selected frame.

Examples (measures in pixels) -
 Assuming display height/width=1024, frame height/width=600:
 300 inside display edge:                   300  =>  300
                                        (+  300) =>  300
 300 inside opposite display edge:      (-  300) => -300
                                           -300  => -300
 300 beyond display edge
  (= 724 inside opposite display edge): (+ -300) => -724
 300 beyond display edge
  (= 724 inside opposite display edge): (- -300) =>  724

In the last two examples, the returned value is relative to the
opposite frame edge from the edge indicated in the input spec."
  (if (consp value)
      (if (natnump (cadr value))
          ;; e.g. (+ 300) or (- 300) => 300 or -300
          (funcall (car value) (cadr value))
        ;; e.g. (+ -300) or (- -300)
        (let ((oppval (- (if (eq 'left type)
                             (x-display-pixel-width)
                           (x-display-pixel-height))
                         (cadr value)
                         (if (eq 'left type)
                             (frame-pixel-width frame)
                           (frame-pixel-height frame)))))
          (if (eq '+ (car value))
              (- oppval)                ; e.g. (+ -300) => -724
            oppval)))                   ; e.g. (- -300) =>  724
    ;; e.g. 300 or -300
    value))

(defun frame-geom-spec-numeric (spec &optional frame)
  "Return equivalent geometry specification for FRAME in numeric terms.
A geometry specification equivalent to SPEC for FRAME is returned,
where the value is numeric, not a consp.
SPEC is a frame geometry spec: (left . VALUE) or (top . VALUE).
If VALUE is a consp, then it is converted to a numeric value, perhaps
   relative to the opposite frame edge from that in the original SPEC.
FRAME defaults to the selected frame.

Examples (measures in pixels) -
 Assuming display height=1024, frame height=600:
 top 300 below display top:               (top .  300) => (top .  300)
                                          (top +  300) => (top .  300)
 bottom 300 above display bottom:         (top -  300) => (top . -300)
                                          (top . -300) => (top . -300)
 top 300 above display top
  (= bottom 724 above display bottom):    (top + -300) => (top . -724)
 bottom 300 below display bottom
  (= top 724 below display top):          (top - -300) => (top .  724)

In the last two examples, the returned value is relative to the
opposite frame edge from the edge indicated in the input SPEC."
  (cons (car spec) (frame-geom-value-numeric (car spec) (cdr spec))))

(defun frame-geom-value-cons (type value &optional frame)
  "Return equivalent geometry value for FRAME as a cons with car `+'.
A geometry value equivalent to VALUE for FRAME is returned,
where the value is a cons with car `+', not numeric.
TYPE is the car of the original geometry spec (TYPE . VALUE).
   It is `top' or `left', depending on which edge VALUE is related to.
VALUE is the cdr of a frame geometry spec: (left/top . VALUE).
If VALUE is a number, then it is converted to a cons value, perhaps
   relative to the opposite frame edge from that in the original spec.
FRAME defaults to the selected frame.

Examples (measures in pixels) -
 Assuming display height/width=1024, frame height/width=600:
 300 inside display edge:                   300  => (+  300)
                                        (+  300) => (+  300)
 300 inside opposite display edge:      (-  300) => (+  124)
                                           -300  => (+  124)
 300 beyond display edge
  (= 724 inside opposite display edge): (+ -300) => (+ -300)
 300 beyond display edge
  (= 724 inside opposite display edge): (- -300) => (+  724)

In the 3rd, 4th, and 6th examples, the returned value is relative to
the opposite frame edge from the edge indicated in the input spec."
  (cond ((and (consp value) (eq '+ (car value))) ; e.g. (+ 300), (+ -300)
         value)
        ((natnump value) (list '+ value)) ; e.g. 300 => (+ 300)
        (t                              ; e.g. -300, (- 300), (- -300)
         (list '+ (- (if (eq 'left type) ; => (+ 124), (+ 124), (+ 724)
                         (x-display-pixel-width)
                       (x-display-pixel-height))
                     (if (integerp value) (- value) (cadr value))
                     (if (eq 'left type)
                         (frame-pixel-width frame)
                       (frame-pixel-height frame)))))))

(defun frame-geom-spec-cons (spec &optional frame)
  "Return equivalent geometry spec for FRAME as a cons with car `+'.
A geometry specification equivalent to SPEC for FRAME is returned,
where the value is a cons with car `+', not numeric.
SPEC is a frame geometry spec: (left . VALUE) or (top . VALUE).
If VALUE is a number, then it is converted to a cons value, perhaps
   relative to the opposite frame edge from that in the original spec.
FRAME defaults to the selected frame.

Examples (measures in pixels) -
 Assuming display height=1024, frame height=600:
 top 300 below display top:               (top .  300) => (top +  300)
                                          (top +  300) => (top +  300)
 bottom 300 above display bottom:         (top -  300) => (top +  124)
                                          (top . -300) => (top +  124)
 top 300 above display top
  (= bottom 724 above display bottom):    (top + -300) => (top + -300)
 bottom 300 below display bottom
  (= top 724 below display top):          (top - -300) => (top +  724)

In the 3rd, 4th, and 6th examples, the returned value is relative to
the opposite frame edge from the edge indicated in the input spec."
  (cons (car spec) (frame-geom-value-cons (car spec) (cdr spec))))