PtLabel

A text, bitmap, or image label

Class hierarchy:

PtWidget → PtBasic → PtLabel

Immediate subclasses:

• PtButton
• PtMenuLabel — see PtMenuButton
• PtTab
• PtText

For more information, see the diagram of the widget hierarchy.

PhAB icon:

Public header:

<photon/PtLabel.h>

Description:

The PtLabel class provides a text string, bitmap, or image for labeling other widgets. You can have text pop up in a balloon to provide further meaning to the label.

A text string in a PtLabel widget.

As their name implies, labels are tags attached to objects to identify their name or nature. Label widgets are usually positioned beside the other widget they're describing, although in some cases (e.g. lists), the label appears above the object.

The most frequent use of a label is to identify the name of an input field. For example, a mail program must provide input fields for indicating the recipient and the subject of a mail message being composed. The label widget lets you attach “To:” and “Subject:” tags to those input fields.

Creating labels

The default label type is a null-terminated text string. To specify the type of label, use the Pt_ARG_LABEL_TYPE resource. The possible values for this resource are:

Pt_Z_STRING

The label is a null-terminated ASCII string. This is the default.

Pt_IMAGE

The label is an image, typically a small icon.

Pt_TEXT_IMAGE

The label displays an image and text. To specify the positioning of these two elements relative to each other, set Pt_ARG_BALLOON_POSITION. Use Pt_ARG_TEXT_IMAGE_SPACING to specify the number of pixels between the image and text.

Different resources are used for the label data for different label types. This is particularly useful when you wish to switch quickly between image labels and text labels, so you can give the user a choice between using icons and textual descriptions of operations.

At the push of a button, the user can switch your interface from an iconic representation of commands to a textual representation of the same labels. You can switch the label from an icon to text simply by changing the label type resource.

Text labels

When the label type is textual, the label widget gets the text to be displayed from the Pt_ARG_TEXT_STRING resource.

To specify the font for the text, set Pt_ARG_TEXT_FONT.

The label widget defines its own margins in addition to the margin width defined by the PtBasic widget class. There are separate left, right, top, and bottom margins, which you can specify using:

• Pt_ARG_MARGIN_LEFT
• Pt_ARG_MARGIN_RIGHT
• Pt_ARG_MARGIN_TOP
• Pt_ARG_MARGIN_BOTTOM

These margins are cumulative, so that the actual margin of one edge of the widget is the corresponding resource value added to the margin width.

The text label may be aligned independently to the left or right margin, or centered horizontally within the margins of the widget. The Pt_ARG_HORIZONTAL_ALIGNMENT resource controls this behavior. Pt_ARG_SECONDARY_H_ALIGN controls how the text is aligned when the label is smaller than the text (that is, when the text is clipped). If this resource is not set, the value from Pt_ARG_HORIZONTAL_ALIGNMENT is used. The values to specify for these horizontal alignment resources are:

• Pt_LEFT
• Pt_RIGHT
• Pt_CENTER

For example, you may want to set Pt_ARG_HORIZONTAL_ALIGNMENT to Pt_CENTER, but ensure that the beginning of the text is readable if the label becomes smaller than the text (for example, if the window is resized, and the label's resize policies allow clipping) by setting Pt_ARG_SECONDARY_V_ALIGN to Pt_LEFT.

You can also control the vertical alignment, i.e. whether the text is aligned to the widget's top or bottom margin, or centered vertically between the two margins. The Pt_ARG_VERTICAL_ALIGNMENT resource controls this behavior. Pt_ARG_SECONDARY_V_ALIGN controls the alignment of clipped text. The values to specify for the vertical alignment are:

• Pt_TOP
• Pt_BOTTOM
• Pt_CENTER

By default, the text displayed in the label widget is left-aligned horizontally, and centered vertically. The baseline is calculated by adding the ascender of the label font to the top margin. When text is aligned to the bottom of the widget, the baseline is calculated by subtracting the descender of the label font from the widget's bottom margin.

You can align the baselines of labels drawn with different fonts by selecting bottom alignment for each of the widgets and choosing appropriate margins for them. In this case, make sure you specify a widget height large enough to accommodate the height of the largest font used.

The desired baseline for your aligned widgets is adjusted by the size of the maximum descender of all the fonts used. For each label, add the difference between this descender and the descender of that label's font, then add this difference to the widget's bottom margin. Keep track of this value so that you can recalculate the correct margin setting if you want to change the base margin or the font later on.

Image and bitmap labels

When the label is an image, the label widget gets the image from the Pt_ARG_LABEL_IMAGE resource, which contains a pointer to an image structure, of type PhImage_t, which is described in the Photon Library Reference.

The members of the image structure used by the label and button widgets are:

type

Specifies the type of image. This determines which other members of the image structure are significant and defines the format of the raw image data.

Images can be palette-based or raw. Palette-based images, including bitmaps, have a color palette that serves as a lookup table for determining what color should be displayed for each pixel. Each pixel in the image is encoded as an index into the lookup table, and the pixel is displayed using the color contained in the corresponding table entry.

Raw images have actual RGB color values encoded in the image data.

More than one pixel may be encoded in each byte of the image data, so image-scan lines are padded out to a byte boundary.

Bitmaps are encoded with 1 bit-per-pixel, with the most significant bit first. The types are:

• Pg_BITMAP_BACKFILL — a bitonal image; the two colors are specified in the color palette.
• Pg_BITMAP_TRANSPARENT — a monochrome image. The bits in the image data that are set to 1 are drawn using color palette entry 1; zeros are treated as transparent, so they're not drawn.

The other types of palette-based images are:

• Pg_IMAGE_PALETTE_BYTE — palette-based image encoded as 8 bits-per-pixel.
• Pg_IMAGE_PALETTE_NIBBLE — palette-based image encoded as 4 bits-per-pixel. The most significant nibble in a byte specifies the leftmost pixel.

Raw images are all encoded using 16, 24, or 32 bits-per-pixel. The types of raw images are:

• Pg_IMAGE_DIRECT_8888 — raw image with 8 bits each for blue, green, and red (with an additional 8 bits reserved).
• Pg_IMAGE_DIRECT_888 — raw image with 8 bits each for blue, green, and red.
• Pg_IMAGE_DIRECT_664 — raw image with 6 bits each for green and red, and 4 bits for blue.
• Pg_IMAGE_DIRECT_1555 — raw image with 5 bits each for blue, green, and red.

bpl

The number of bytes used to encode each scan line. This depends on the image type and size.

size

The width and height of the image in pixels.

colors

The number of colors used in the image for palette-based images. It's used for determining how many color palette entries are significant.

palette

The color lookup table for determining the color of each pixel in the image.

image

The raw image data.

For more information about manipulating images and image data formats, see the Raw Drawing and Animation chapter of the Photon Programmer's Guide.

Balloons

Balloons are a very handy feature of the PtLabel widget class. You can use a balloon to display a line of text when the pointer pauses on top of a widget for more than a second.

This can be very useful in an application with a lot of icons. Whenever you pause on an icon, a little text box pops up beside it to display the name or action the icon represents.

To use balloons with label class widgets:

1. Set the Pt_SHOW_BALLOON bit in the Pt_ARG_LABEL_FLAGS resource.
2. Set the Pt_ARG_BALLOON_POSITION resource to define the location.

The Pt_ARG_BALLOON_TEXT resource defines the text displayed in the balloon. If this resource is not set, the Pt_ARG_TEXT_STRING is displayed instead. This allows you to choose one of the two main uses of balloons, either to give further information to the user, or to display the label text in cases where the label has been truncated.

New resources:

Pt_ARG_ACCEL_KEY

The accelerator key to underline within the widget's text string. You typically use this resource for hotkeys.

Pt_ARG_BALLOON_COLOR

The balloon's text color. See PgColor_t in the Photon Library Reference.

Pt_ARG_BALLOON_FILL_COLOR

The balloon's fill color. See PgColor_t in the Photon Library Reference.

Pt_ARG_BALLOON_POSITION

Indicates where the balloon with the label's text pops up. If Pt_ARG_LABEL_TYPE is Pt_TEXT_IMAGE, this resource also controls the positioning of the text and image elements relative to each other. Possible values:

• Pt_BALLOON_INPLACE
• Pt_BALLOON_TOP
• Pt_BALLOON_LEFT
• Pt_BALLOON_RIGHT
• Pt_BALLOON_BOTTOM

Pt_ARG_BALLOON_TEXT

The text string to display in the balloon. If left blank, the Pt_ARG_TEXT_STRING is used for balloons.

Pt_ARG_HORIZONTAL_ALIGNMENT

The horizontal alignment for the text string. Possible values:

• Pt_LEFT
• Pt_CENTER
• Pt_RIGHT

Pt_ARG_LABEL_BALLOON

By default, when you pause the pointer over this widget, the widget displays a small balloon. If you want to change the look of the balloon, you can use this resource to override the default inflate function.

Here's the prototype of the inflate function:

PtWidget_t * InflateBalloon( PtWidget_t *window,
                             PtWidget_t *widget,
                             int position,
                             char *text,
                             char *font,
                             PgColor_t fill_color,
                             PgColor_t text_color );
        

The arguments are:

window

The window widget of the widget that requires the balloon.

widget

The widget that requires the balloon.

position

Where the balloon is to pop up:

• Pt_BITMAP_BALLOON_BOTTOM
• Pt_BITMAP_BALLOON_INPLACE
• Pt_BITMAP_BALLOON_LEFT
• Pt_BITMAP_BALLOON_RIGHT
• Pt_BITMAP_BALLOON_TOP

text

The text to display in the balloon.

font

The font for the text.

fill_color

The balloon's fill color.

text_color

The color of text in the balloon.

You can use the supplied values in your inflate function or ignore them and use your own values.

Pt_ARG_LABEL_FLAGS

Possible values:

Pt_BACKFILL_TEXT

If this is set, the widget fills the text background with the widget's fill color before rendering the text.

Pt_LABEL_SELECT_SHIFT

If this is set, the text shifts down and to the right by one pixel when the widget is armed. Otherwise, the text doesn't shift.

Pt_SHOW_BALLOON

If the pointer remains motionless for 1.25 seconds over the label, a balloon pops up with the label's text.

Pt_BALLOON_AS_REQUIRED

Same as Pt_SHOW_BALLOON, except the balloon is inflated only if the label is clipped by its parent container.

Pt_USE_ELLIPSIS

Replace part of the text with an ellipsis (…) if there isn't enough space to display all of it.

Pt_ELLIPSIS_MIDDLE

Put the ellipsis into the middle of the text string, instead of at its end(s). This flag is used only when you've set Pt_USE_ELLIPSIS.

Pt_ARG_LABEL_IMAGE

A pointer to a PhImage_t structure (see the Photon Library Reference) that defines the image to be used if the label type (see Pt_ARG_LABEL_TYPE, below) is Pt_IMAGE or Pt_TEXT_IMAGE.

---

When you set this resource, the widget copies the PhImage_t structure but not the data pointed to by the members of the structure. After setting this resource, you can free() the PhImage_t if you don't need it, but don't free() the members of it.

---

Set the flags member of the PhImage_t structure to:

Ph_RELEASE_IMAGE | Ph_RELEASE_PALETTE |
Ph_RELEASE_TRANSPARENCY_MASK | Ph_RELEASE_GHOST_BITMAP

before providing the image to the widget. If you do this, the memory used for the image is released when image is replaced or the widget is unrealized or destroyed.

Pt_ARG_LABEL_TYPE

The type of information displayed by the label. Possible values:

Pt_Z_STRING

Use Pt_ARG_TEXT_STRING to display the text.

Pt_IMAGE

Use Pt_ARG_LABEL_IMAGE to display an image.

Pt_TEXT_IMAGE

Display the image and text of the label. You can specify the positioning of these two elements relative to each other by setting Pt_ARG_BALLOON_POSITION.

Pt_ARG_LINE_SPACING

The space, in pixels, between the lines of text in the label.

Pt_ARG_MARGIN_BOTTOM

The amount of space between the bottom of the label's canvas and the canvas defined by the basic widget.

Pt_ARG_MARGIN_LEFT

The amount of space between the left side of the label's canvas and the canvas defined by the basic widget.

Pt_ARG_MARGIN_RIGHT

The amount of space between the right side of the label's canvas and the canvas defined by the basic widget.

Pt_ARG_MARGIN_TOP

The amount of space between the top of the label's canvas and the canvas defined by the basic widget.

Pt_ARG_SECONDARY_H_ALIGN

The horizontal alignment for the text string, if the text string is clipped. Possible values:

• Pt_LEFT
• Pt_CENTER
• Pt_RIGHT

Pt_ARG_SECONDARY_V_ALIGN

The vertical alignment for the text string, if the text string is clipped. Possible values:

• Pt_TOP
• Pt_CENTER
• Pt_BOTTOM

Pt_ARG_TEXT_FONT

The font used for the label's text string; see PgSetFont().

Pt_ARG_TEXT_IMAGE_SPACING

The space, in pixels, between the text and the image in the label.

Pt_ARG_TEXT_STRING

The text string to be displayed if Pt_ARG_LABEL_TYPE is Pt_Z_STRING or Pt_TEXT_IMAGE, as well as the text to display in the balloon if Pt_ARG_BALLOON_TEXT is blank.

Pt_ARG_UNDERLINE1

The underline color for the first line.

Pt_ARG_UNDERLINE2

The underline color for the second line (used to create thick or beveled underlines).

Pt_ARG_UNDERLINE_TYPE

The type of underline. Possible values:

• Pt_NO_ULINE
• Pt_DOUBLE_ULINE (use with underline color)
• Pt_SINGLE_ULINE (use with underline color)
• Pt_ULINE_ETCHED_IN (use with border color)
• Pt_ULINE_ETCHED_OUT (use with border color)

Pt_ARG_VERTICAL_ALIGNMENT

The vertical alignment for the text string. Possible values:

• Pt_TOP
• Pt_CENTER
• Pt_BOTTOM

Inherited resources:

If the widget modifies an inherited resource, the “Default override” column indicates the new value. This modification affects any subclasses of the widget.