Motif Programmer's Guide Migration Version

Motif 2.1 Programmer's Guide

Managing Geometry Using Form

Form is a container widget that provides the most comprehensive facilities for controlling the layout of children. Constraints are placed on children of the Form to define attachments for each of the child's four sides. These attachments can be to the Form, to another child widget or gadget, to a relative position within the Form, or to the initial position of the child. The attachments determine the layout behavior of the Form when resizing occurs. Form is a subclass of BulletinBoard, so the resources and general geometry policies of BulletinBoard apply to Form as well.

Each child has 17 Form constraint resources, four for each side of the child and one, XmNresizable, that applies to the child as a whole. Following is a description of XmNresizable and the constraint resources that apply to the top side of a child:

XmNresizable

This Boolean resource specifies whether or not a child's request for a new size is (conditionally) granted by the Form. If this resource is set to True, the request is granted if possible. If this resource is set to False, the request is always refused.

If a child has both left and right attachments, its width is completely controlled by the Form, regardless of the value of the child's XmNresizable resource. Similarly, if a child has both top and bottom attachments, its height is completely controlled by the Form, regardless of the value of the child's XmNresizable resource. If a child has a left or right attachment but not both, the child's XmNwidth is used in setting its width if the value of the child's XmNresizable resource is True. These conditions are also true for top and bottom attachments, with height acting like width.

XmNtopAttachment

Specifies attachment of the top side of the child. It can have the following values:

XmATTACH_NONE

Do not attach the top side of the child. If XmNbottomAttachment is also XmATTACH_NONE, this value is ignored and the child is given a default top attachment.

XmATTACH_FORM

Attach the top side of the child to the top side of the Form.

XmATTACH_OPPOSITE_FORM

Attach the top side of the child to the bottom side of the Form. XmNtopOffset can be used to determine the visibility of the child.

XmATTACH_WIDGET

Attach the top side of the child to the bottom side of the widget or gadget specified in the XmNtopWidget resource. If XmNtopWidget is NULL, XmATTACH_WIDGET is replaced by XmATTACH_FORM, and the child is attached to the top side of the Form.

XmATTACH_OPPOSITE_WIDGET

Attach the top side of the child to the top side of the widget or gadget specified in the XmNtopWidget resource.

XmATTACH_POSITION

Attach the top side of the child to a position that is relative to the top side of the Form and in proportion to the height of the Form. This position is determined by the XmNtopPosition and XmNfractionBase resources.

XmATTACH_SELF

Attach the top side of the child to a position that is proportional to the current y value of the child divided by the height of the Form. This position is determined by the XmNtopPosition and XmNfractionBase resources. XmNtopPosition is set to a value proportional to the current y value of the child divided by the height of the Form.

XmNtopOffset

Specifies the constant offset between the top side of the child and the object to which it is attached. The relationship established remains, regardless of any resizing operations that occur.

XmNtopPosition

This resource is used to determine the position of the top side of the child when the child's XmNtopAttachment is set to XmATTACH_POSITION. In this case, the position of the top side of the child is relative to the top side of the Form and is a fraction of the height of the Form. This fraction is the value of the child's XmNtopPosition resource divided by the value of the Form's XmNfractionBase. For example, if the child's XmNtopPosition is 50, the Form's XmNfractionBase is 100, and the Form's height is 200, the position of the top side of the child is 100.

XmNtopWidget

Specifies the widget or gadget to which the top side of the child is attached. This resource is used if XmNtopAttachment is set to either XmATTACH_WIDGET or XmATTACH_OPPOSITE_WIDGET.

These constraint resources interact with the following resources of the Form itself:

XmNfractionBase

Specifies the denominator used in calculating the relative position of a child widget using XmATTACH_POSITION constraints. The value must not be 0.

If the value of a child's XmNleftAttachment (or XmNrightAttachment) is XmATTACH_POSITION, the position of the left (or right) side of the child is relative to the left side of the Form and is a fraction of the width of the Form. This fraction is the value of the child's XmNleftPosition (or XmNrightPosition) resource divided by the value of the Form's XmNfractionBase.

If the value of a child's XmNtopAttachment (or XmNbottomAttachment) is XmATTACH_POSITION, the position of the top (or bottom) side of the child is relative to the top side of the Form and is a fraction of the height of the Form. This fraction is the value of the child's XmNtopPosition (or XmNbottomPosition) resource divided by the value of the Form's XmNfractionBase.

XmNhorizontalSpacing

Specifies the offset for right and left attachments.

XmNrubberPositioning

Indicates the default near (left) and top attachments for a child of the Form.

Note:

Whether this resource actually applies to the left or right side of the child and its attachment may depend on the value of the XmNstringDirection resource.)

The default left attachment is applied whenever initialization or XtSetValues leaves the child without either a left or right attachment. The default top attachment is applied whenever initialization or XtSetValues leaves the child without either a top or bottom attachment.

If this Boolean resource is set to False, XmNleftAttachment and XmNtopAttachment default to XmATTACH_FORM, XmNleftOffset defaults to the current x value of the left side of the child, and XmNtopOffset defaults to the current y value of the child. The effect is to position the child according to its absolute distance from the left or top side of the Form.

If this resource is set to True, XmNleftAttachment and XmNtopAttachment default to XmATTACH_POSITION, XmNleftPosition defaults to a value proportional to the current x value of the left side of the child divided by the width of the Form, and XmNtopPosition defaults to a value proportional to the current y value of the child divided by the height of the Form. The effect is to position the child relative to the left or top side of the Form and in proportion to the width or height of the Form.

XmNverticalSpacing

Specifies the offset for top and bottom attachments.

Following are some important considerations in using a Form:

Every child must have an attachment on either the left or the right. If initialization or XtSetValues leaves a widget without such an attachment, the result depends upon the value of XmNrubberPositioning.

If XmNrubberPositioning is False, the child is given an XmNleftAttachment of XmATTACH_FORM and an XmNleftOffset equal to its current x value.

If XmNrubberPositioning is True, the child is given an XmNleftAttachment of XmATTACH_POSITION and an XmNleftPosition proportional to the current x value divided by the width of the Form.

In either case, if the child has not been previously given an x value, its x value is taken to be 0, which places the child at the left side of the Form.

If you want to create a child without any attachments, and then later (for example, after creating and managing it, but before realizing it) give it a right attachment using XtSetValues, you must set its XmNleftAttachment to XmATTACH_NONE at the same time.

The XmNresizable resource controls only whether a geometry request by the child will be granted. It has no effect on whether the child's size can be changed because of changes in geometry of the Form or of other children.

Every child has a preferred width, based on geometry requests it makes (whether they are granted or not).

If a child has attachments on both the left and the right sides, its width is completely controlled by the Form. It can be shrunk below its preferred width or enlarged above it, if necessary, due to other constraints. In addition, the child's geometry requests to change its own width may be refused.

If a child has attachments on only its left or right side, it will always be at its preferred width (if resizable, otherwise at is current width). This may cause it to be clipped by the Form or by other children.

If a child's left (or right) attachment is set to XmATTACH_SELF, its corresponding left (or right) offset is forced to 0. The attachment is then changed to XmATTACH_POSITION, with a position that corresponds to the x value of the child's left (or right) edge. To fix the position of a side at a specific x value, use XmATTACH_FORM or XmATTACH_OPPOSITE_FORM with the x value as the left (or right) offset.

Unmapping a child has no effect on the Form except that the child is not mapped.

Unmanaging a child unmaps it. If no other child is attached to it, or if all children attached to it and all children recursively attached to them are also all unmanaged, all of those children are treated as if they did not exist in determining the size of the Form.

When using XtSetValues to change the XmNx resource of a child, you must simultaneously set its left attachment to either XmATTACH_SELF or XmATTACH_NONE. Otherwise, the request is not granted. If XmNresizable is False, the request is granted only if the child's size can remain the same.

A left (or right) attachment of XmATTACH_WIDGET, where XmNleftWidget (or XmNrightWidget) is NULL, acts like an attachment of XmATTACH_FORM.

If an attachment is made to a widget that is not a child of the Form, but an ancestor of the widget is a child of the Form, the attachment is made to the ancestor.

All these considerations are true of top and bottom attachments as well, with top acting like left, bottom acting like right, y acting like x, and height acting like width.