# Scrollbar Widget

    Application header file     <X11/Xaw/Scrollbar.h>
    Class header file           <X11/Xaw/ScrollbarP.h>
    Class                       scrollbarWidgetClass
    Class Name                  Scrollbar
    Superclass                  Simple

A Scrollbar widget is a rectangle, called the canvas, on which another rectangle, the thumb, moves in one dimension, either vertically or horizontally. A Scrollbar can be used alone, as a value generator, or it can be used within a composite widget (for example, a Viewport). When a Scrollbar is used to move, or scroll, the contents of another widget, the size and the position of the thumb usually give feedback as to what portion of the other widget's contents are visible.

Each pointer button invokes a specific action. Pointer buttons 1 and 3 do not move the thumb automatically. Instead, they return the pixel position of the cursor on the scroll region. When pointer button 2 is clicked, the thumb moves to the current pointer position. When pointer button 2 is held down and the pointer is moved, the thumb follows the pointer.

The pointer cursor in the scroll region changes depending on the current action. When no pointer button is pressed, the cursor appears as a double-headed arrow that points in the direction that scrolling can occur. When pointer button 1 or 3 is pressed, the cursor appears as a single-headed arrow that points in the logical direction that the thumb will move. When pointer button 2 is pressed, the cursor appears as an arrow that points to the top or the left of the thumb.

When the user scrolls, the application receives notification through callback procedures. For both discrete scrolling actions, the callback returns the Scrollbar widget, the client_data, and the pixel position of the pointer when the button was released. For continuous scrolling, the callback routine returns the scroll bar widget, the client data, and the current relative position of the thumb. When the thumb is moved using pointer button 2, the callback procedure is invoked continuously. When either button 1 or 3 is pressed, the callback procedure is invoked only when the button is released and the client callback procedure is responsible for moving the thumb.

## Resources

When creating a Scrollbar widget instance, the following resources are retrieved from the argument list or from the resource database:

Name | Class | Type | Notes | Default Value
accelerators | Accelerators | AcceleratorTable |  | NULL
ancestorSensitive | AncestorSensitive | Boolean | D | True
background | Background | Pixel |  | XtDefaultBackground
backgroundPixmap | Pixmap | Pixmap |  | XtUnspecifiedPixmap
borderColor | BorderColor | Pixel |  | XtDefaultForeground
borderPixmap | Pixmap | Pixmap |  | XtUnspecifiedPixmap
borderWidth | BorderWidth | Dimension |  | 1
colormap | Colormap | Colormap |  | parent's Colormap
cursor | Cursor | Cursor |  | None
cursorName | Cursor | String |  | NULL
depth | Depth | int | C | parent's Depth
destroyCallback | Callback | XtCallbackList |  | NULL
foreground | Foreground | Pixel |  | XtDefaultForeground
height | Height | Dimension | A | depends on orientation
insensitiveBorder | Insensitive | Pixmap |  | GreyPixmap
international | International | Boolean | C | False
jumpProc | Callback | XtCallbackList |  | NULL
length | Length | Dimension |  | 1
mappedWhenManaged | MappedWhenManaged | Boolean |  | True
minimumThumb | MinimumThumb | Dimension |  | 7
orientation | Orientation | Orientation |  | XtorientVertical (vertical)
pointerColor | Foreground | Pixel |  | XtDefaultForeground
pointerColorBackground | Background | Pixel |  | XtDefaultBackground
screen | Screen | Screen | R | parent's Screen
scrollDCursor | Cursor | Cursor |  | XC_sb_down_arrow
scrollHCursor | Cursor | Cursor |  | XC_sb_h_double_arrow
scrollLCursor | Cursor | Cursor |  | XC_sb_left_arrow
scrollProc | Callback | XtCallbackList |  | NULL
scrollRCursor | Cursor | Cursor |  | XC_sb_right_arrow
scrollUCursor | Cursor | Cursor |  | XC_sb_up_arrow
scrollVCursor | Cursor | Cursor |  | XC_sb_v_arrow
sensitive | Sensitive | Boolean |  | True
shown | Shown | Float |  | 0.0
thickness | Thickness | Dimension |  | 14
thumb | Thumb | Bitmap |  | GreyPixmap
thumbProc | Callback | XtCallbackList |  | NULL
topOfThumb | TopOfThumb | Float |  | 0.0
translations | Translations | TranslationTable |  | See below
width | Width | Dimension | A | depends on orientation
x | Position | Position |  | 0
y | Position | Position |  | 0

`foreground`

- A pixel value which indexes the widget's colormap to derive the color used to draw the thumb.

`jumpProc`

- All functions on this callback list are called when the `NotifyThumb` action is invoked. See Scrollbar_Actions for details.

`length`

- The height of a vertical scrollbar or the width of a horizontal scrollbar.

`minimumThumb`

- The smallest size, in pixels, to which the thumb can shrink.

`orientation`

- The orientation is the direction that the thumb will be allowed to move. This value can be either `XtorientVertical` or `XtorientHorizontal`.

`scrollDCursor`

- This cursor is used when scrolling backward in a vertical scrollbar.

`scrollHCursor`

- This cursor is used when a horizontal scrollbar is inactive.

`scrollLCursor`

- This cursor is used when scrolling forward in a horizontal scrollbar.

`scrollProc`

- All functions on this callback list may be called when the `NotifyScroll` action is invoked. See Scrollbar_Actions for details.

`scrollRCursor`

- This cursor is used when scrolling backward in a horizontal scrollbar, or when thumbing a vertical scrollbar.

`scrollUCursor`

- This cursor is used when scrolling forward in a vertical scrollbar, or when thumbing a horizontal scrollbar.

`scrollVCursor`

- This cursor is used when a vertical scrollbar is inactive.

`shown`

- This is the size of the thumb, expressed as a percentage (0.0 - 1.0) of the length of the scrollbar.

`thickness`

- The width of a vertical scrollbar or the height of a horizontal scrollbar.

`thumb`

- This pixmap is used to tile (or stipple) the thumb of the scrollbar. If no tiling is desired, then set this resource to `None`. This resource will accept either a bitmap or a pixmap that is the same depth as the window. The resource converter for this resource constructs bitmaps from the contents of files. (See `Converting Bitmaps` for details.)

`topOfThumb`

- The location of the top of the thumb, as a percentage (0.0 - 1.0) of the length of the scrollbar. This resource was called `top` in previous versions of the Athena widget set. The name collided with the a Form widget constraint resource, and had to be changed.

## Scrollbar Actions

The actions supported by the Scrollbar widget are:

`StartScroll`(value)

- The possible values are Forward, Backward, or Continuous. This must be the first action to begin a new movement.

`NotifyScroll`(value)

- The possible values are Proportional or FullLength. If the argument to StartScroll was Forward or Backward, NotifyScroll executes the `scrollProc` callbacks and passes either; the position of the pointer, if value is Proportional, or the full length of the scroll bar, if value is FullLength. If the argument to StartScroll was Continuous, NotifyScroll returns without executing any callbacks.

`EndScroll`( )

- This must be the last action after a movement is complete.

`MoveThumb`( )

- Repositions the Scrollbar's thumb to the current pointer location.

`NotifyThumb`( )\

- Calls the callbacks and passes the relative position of the pointer as a percentage of the scroll bar length.

The default bindings for Scrollbar are:

         <Btn1Down>:     StartScroll(Forward)
         <Btn2Down>:     StartScroll(Continuous) MoveThumb( ) NotifyThumb( )
         <Btn3Down>:     StartScroll(Backward)
         <Btn2Motion>:     MoveThumb( ) NotifyThumb( )
         <BtnUp>:     NotifyScroll(Proportional) EndScroll( )

Examples of additional bindings a user might wish to specify in a resource file are:

    *Scrollbar.Translations: \\
         ~Meta<Key>space:     StartScroll(Forward) NotifyScroll(FullLength) \\n\\
          Meta<Key>space:     StartScroll(Backward) NotifyScroll(FullLength) \\n\\
              EndScroll( )

## Scrollbar Callbacks

There are two callback lists provided by the Scrollbar widget. The procedural interface for these functions is described here.

The calling interface to the `scrollProc` callback procedure is:

      void ScrollProc
      Widget scrollbar
      XtPointer client_data
      XtPointer position

scrollbar

- Specifies the Scrollbar widget.

client_data

- Specifies the client data.

position

- Specifies a pixel position in integer form.

The `scrollProc` callback is used for incremental scrolling and is called by the `NotifyScroll` action. The position argument is a signed quantity and should be cast to an int when used. Using the default button bindings, button 1 returns a positive value, and button 3 returns a negative value. In both cases, the magnitude of the value is the distance of the pointer in pixels from the top (or left) of the Scrollbar. The value will never be greater than the length of the Scrollbar.

The calling interface to the `jumpProc` callback procedure is:

      void JumpProc
      Widget scrollbar
      XtPointer client_data
      XtPointer percent_ptr

scrollbar

- Specifies the ID of the scroll bar widget.

client_data

- Specifies the client data.

percent_ptr

- Specifies the floating point position of the thumb (0.0 – 1.0).

The `jumpProc` callback is used to implement smooth scrolling and is called by the `NotifyThumb` action. Percent_ptr must be cast to a pointer to float before use; i.e.

         float percent = *(float*)percent_ptr;

With the default button bindings, button 2 moves the thumb interactively, and the `jumpProc` is called on each new position of the pointer, while the pointer button remains down. The value specified by percent_ptr is the current location of the thumb (from the top or left of the Scrollbar) expressed as a percentage of the length of the Scrollbar.

## Convenience Routines

To set the position and length of a Scrollbar thumb, use

      void XawScrollbarSetThumb
      Widget w
      float top
      float shown

w

- Specifies the Scrollbar widget.

top

- Specifies the position of the top of the thumb as a fraction of the length of the Scrollbar.

shown

- Specifies the length of the thumb as a fraction of the total length of the Scrollbar.

`XawScrollbarThumb` moves the visible thumb to a new position (0.0 – 1.0) and length (0.0 – 1.0). Either the top or shown arguments can be specified as -1.0, in which case the current value is left unchanged. Values greater than 1.0 are truncated to 1.0.

If called from `jumpProc`, XawScrollbarSetThumb has no effect.

## Setting Float Resources

The `shown` and `topOfThumb` resources are of type float. These resources can be difficult to get into an argument list. The reason is that C performs an automatic cast of the float value to an integer value, usually truncating the important information. The following code fragment is one portable method of getting a float into an argument list.

         top = 0.5;
         if (sizeof(float) > sizeof(XtArgVal)) {
         /*
          * If a float is larger than an XtArgVal then pass this
          * resource value by reference.
          */
              XtSetArg(args[0], XtNshown, &top);
         }
         else {
         /*
          * Convince C not to perform an automatic conversion, which
          * would truncate 0.5 to 0.
          */
              XtArgVal * l_top = (XtArgVal *) &top;
              XtSetArg(args[0], XtNshown, *l_top);
         }