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, 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 underlined-on and underlined-off are:

• #f (acts like 'base)
• #t

The possible values for trasnparent-text-backing-on and trasnparent-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-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-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)
      v : boolean

  The initialization arguments are passed on to set-delta.

  
  

• 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-mult
• 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-mult
• 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