Volume 7A: XView Programming Manual

Example 10-3. Scrollbar compute scroll procedure example (continued)

xv_set(sb, SCROLLBAR_VIEW_LENGTH, last_plus_one - first,

0);

*offset = first;

return (XV_OK);

}

In this example, the textsw package keeps track of the object size based on the number of

characters in the view. When the user scrolls, the object length will most probably change, so

the textsw package uses its own compute scroll procecure to calculate a new object length

and offset each time there is a scroll request. This is needed for cases when the user scrolls

backwards and data is still coming into the textsw, so the object length grows (the propor-

tional indicator shrinks).

10.4.2.1 Indicating scrollbar motion

The attribute

SCROLLBAR_MOTION provides the scrolling motion that resulted during a

scrollbar_request event. This attribute is get only. Possible valid motions returned are:

ABSOLUTE

POINT_TO_MIN (from here_to_top on menu)

PAGE_FORWARD

LINE_FORWARD

MIN_TO_POINT (from top_to_here on menu)

PAGE_BACKWARD

LINE_BACKWARD

TO_END

TO_START

PAGE_ALIGNED

10.4.3 Providing a Scrollbar Normalize Procedure

The scrollbar package provides for a special offset routine that may be used to adjust the new

scroll position before the scrollbar package scrolls to the starting location computed by the

scrollbar compute procedure. This special offset routine, called the normalize procedure,

allows you to perform a scroll adjustment when, for example, the new scroll position would

split an object in the view. By default, no normalize procedure is specified and the scrollbar

package scrolls to the starting location computed by the compute procedure, as shown in the

previous section. Use

SCROLLBAR_NORMALIZE_PROC

to name a normalize procedure used to

adjust the offset.

The function set with SCROLLBAR_NORMALIZE_PROC should return vstart. The function takes

the offset given by the compute_proc and adjusts it. The scrollbar package will then

scroll to this offset into the object. The form of the normalize scroll routine is:

void

my_scrollbar_normalize_proc(sb, voffset, motion, vstart)

Scrollbar sb;

long unsigned offset;

268 XView Programming Manual

Scroll_motion motion;

long unsigned *vstart; /* new offset, this is the new view start*/

See the following example:

Example 10-4. Scrollbar normalize procedure example

panel_normalize_scroll(sb, offset, motion, vs)

Scrollbar sb;

long unsigned offset;

Scroll_motion motion;

long unsigned *vs; /* new offset == new viewstart */

{

line_ht = (int) xv_get(sb, SCROLLBAR_PIXELS_PER_UNIT);

/* If everything in the panel is in view, then don’t scroll. */

if ((int) xv_get(sb, SCROLLBAR_OBJECT_LENGTH) <=

(int) xv_get(sb, SCROLLBAR_VIEW_LENGTH))

return (*vs = offset);

switch (motion) {

case SCROLLBAR_ABSOLUTE:

case SCROLLBAR_LINE_FORWARD:

case SCROLLBAR_TO_START:

align_to_max = TRUE;

scrolling_up = TRUE;

break;

case SCROLLBAR_PAGE_FORWARD:

case SCROLLBAR_TO_END:

align_to_max = TRUE;

scrolling_up = TRUE;

break;

case SCROLLBAR_POINT_TO_MIN:

align_to_max = TRUE;

scrolling_up = TRUE;

break;

case SCROLLBAR_MIN_TO_POINT:

align_to_max = TRUE;

scrolling_up = FALSE;

break;

case SCROLLBAR_PAGE_BACKWARD:

case SCROLLBAR_LINE_BACKWARD:

align_to_max = FALSE;

scrolling_up = FALSE;

break;

}

*vs = offset;

return (XV_OK);

}

Scrollbars

Scrollbars 269

The panel package uses this to ensure panel items are aligned properly and partial items are

not visible. The scrollbar package calls scrollbar_compute_scroll_proc and

scrollbar_normalize_proc in that order whenever any scrolling is done.

10.5 Scrollbar Package Summary

The procedures and macros in the SCROLLBAR package are listed in the next two tables.

Table 10-1 lists the procedure for the SCROLLBAR package. Table 10-2 lists the attributes in

the SCROLLBAR package. This information is described fully in the XView Reference Man-

ual.

Table 10-1. Scrollbar Procedures

scrollbar_paint()

scrollbar_default_compute_scroll_proc()

Table 10-2. Scrollbar Attributes

SCROLLBAR_DIRECTION SCROLLBAR_PAGE_LENGTH

SCROLLBAR_LAST_VIEW_START SCROLLBAR_PIXELS_PER_UNIT

SCROLLBAR_MENU SCROLLBAR_SPLITTABLE

SCROLLBAR_NOTIFY_CLIENT SCROLLBAR_VIEW_LENGTH

SCROLLBAR_OBJECT_LENGTH SCROLLBAR_VIEW_START

SCROLLBAR_MOTION

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