9.29  style-delta%

A style-delta% object encapsulates a style change. The changes expressible by a delta include:

• changing the font family

• changing the font face

• changing the font size to a new value

• enlarging the font by an additive amount

• enlarging the font by a multiplicative amount, etc.

• changing the font style (normal, italic, or slant)

• toggling the font style

• changing the font to italic if it is currently slant, etc.

• changing the font weight, etc.

• changing the underline, etc.

• changing the vertical alignment, etc.

• changing the foreground color

• dimming or brightening the foreground color, etc.

• changing the background color, etc.

• changing text backing transparency

The set-delta method is convenient for most style delta settings; it takes a high-level delta specification and sets the internal delta information.

To take full advantage of a style delta, it is necessary to understand the internal on/off settings that can be manipulated through methods such as set-weight-on. For example, the font weight change is specified through the weight-on and weight-off internal settings. Roughly, weight-on turns on a weight setting when it is not present and weight-off turns off a weight setting when it is present. These two interact precisely in the following way:

• If both weight-on and weight-off are set to 'base, then the font weight is not changed.

• If weight-on is not 'base, then the weight is set to weight-on.

• If weight-off is not 'base, then the weight will be set back to 'normal when the base style has the weight weight-off.

• If both weight-on and weight-off are set to the same value, then the weight is toggled with respect to that value: if the base style has the weight weight-on, then weight is changed to 'normal; if the base style has a different weight, it is changed to weight-on.

• If both weight-on and weight-off are set, but to different values, then the weight is changed to weight-on only when the base style has the weight weight-off.

Font styles, smoothing, underlining, and alignment work in an analogous manner.

The possible values for alignment-on and alignment-off are:

• 'base

• 'top

• 'center

• 'bottom

The possible values for style-on and style-off are:

• 'base

• 'normal

• 'italic

• 'slant

The possible values for smoothing-on and smoothing-off are:

• 'base

• 'default

• 'partly-smoothed

• 'smoothed

• 'unsmoothed

The possible values for underlined-on and underlined-off are:

• #f (acts like 'base)

• #t

The possible values for size-in-pixels-on and size-in-pixels-off are:

• #f (acts like 'base)

• #t

The possible values for transparent-text-backing-on and transparent-text-backing-off are:

• #f (acts like 'base)

• #t

The possible values for weight-on and weight-off are:

• 'base

• 'normal

• 'bold

• 'light

The family and face settings in a style delta are interdependent:

• When a delta's face is #f and its family is 'base, then neither the face nor family are modified by the delta.

• When a delta's face is a string and its family is 'base, then only face is modified by the delta.

• When a delta's family is not 'base, then both the face and family are modified by the delta. If the delta's face is #f, then applying the delta sets a style's face to #f, so that the family setting prevails in choosing a font.

• (make-object style-delta% change-command) -> style-delta% object
     change-command = 'change-nothing : symbol in '(change-nothing change-normal change-toggle-underline change-toggle-size-in-pixels change-normal-color change-bold)

  
  

• (make-object style-delta% change-command v) -> style-delta% object
     change-command : symbol in '(change-family change-style change-toggle-style change-weight change-toggle-weight change-smoothing change-toggle-smoothing change-alignment)
   v : symbol

  
  

• (make-object style-delta% change-command v) -> style-delta% object
     change-command : symbol in '(change-size change-bigger change-smaller)
   v : exact integer in [0, 255]

  
  

• (make-object style-delta% change-command v) -> style-delta% object
     change-command : symbol in '(change-underline change-size-in-pixels)
   v : boolean

  The initialization arguments are passed on to set-delta.

  
  

Methods
    collapse
    copy
    equal?
    get-alignment-off
    get-alignment-on
    get-background-add
    get-background-mult
    get-face
    get-family
    get-foreground-add
    get-foreground-mult
    get-size-add
    get-size-in-pixels-off
    get-size-in-pixels-on
    get-size-mult
    get-smoothing-off
    get-smoothing-on
    get-style-off
    get-style-on
    get-transparent-text-backing-off
    get-transparent-text-backing-on
    get-underlined-off
    get-underlined-on
    get-weight-off
    get-weight-on
    set-alignment-off
    set-alignment-on
    set-delta
    set-delta-background
    set-delta-face
    set-delta-foreground
    set-face
    set-family
    set-size-add
    set-size-in-pixels-off
    set-size-in-pixels-on
    set-size-mult
    set-smoothing-off
    set-smoothing-on
    set-style-off
    set-style-on
    set-transparent-text-backing-off
    set-transparent-text-backing-on
    set-underlined-off
    set-underlined-on
    set-weight-off
    set-weight-on