InvertEffectLib — Plan9Basic Documentation

InvertEffectLib — Colour Inversion

Creates a photographic negative by inverting all pixel colours. Black becomes white, red becomes cyan, blue becomes yellow. Wraps FireMonkey’s TInvertEffect. This is a binary effect — on or off, no intensity parameter. 10 functions.

Category	Count	Description
Error Handling	4	invert_error, errormsg$, strerror$, clearerror
Creation & Destruction	2	invert# (create), invert_free (destroy)
Effect Control	4	enabled, trigger (get/set)

ⓘ Simplest effect: InvertEffectLib has no adjustable properties (no amount, colour, or intensity). It simply flips all colours to their complement. Use invert_enabled# to toggle on/off.

Colour Inversions

Each pixel’s RGB channels are inverted: new = 255 - original. Alpha is preserved.

Original	Inverted	Formula
Black (0,0,0)	White (255,255,255)	255−0 = 255
White (255,255,255)	Black (0,0,0)	255−255 = 0
Red (255,0,0)	Cyan (0,255,255)	Complementary pair
Green (0,255,0)	Magenta (255,0,255)	Complementary pair
Blue (0,0,255)	Yellow (255,255,0)	Complementary pair
Orange (255,165,0)	Blue (0,90,255)	Channel-wise inversion
Gray 50% (128,128,128)	Gray 50% (127,127,127)	Mid-gray stays mid-gray

ⓘ Double invert = original: Applying invert twice returns to the original colours. Inverting an already inverted image restores it perfectly.

Cross-Platform Support

Platform	Status
Windows	✅ Full Support
Linux	✅ Full Support
Android	✅ Full Support

Error Handling

Function	Signature	Description
`invert_error()`	`invert_error@`	Returns last error code (0 = no error)
`invert_errormsg$()`	`invert_errormsg$@`	Returns last error message
`invert_strerror$(code)`	`invert_strerror$@n`	Converts error code to text
`invert_clearerror()`	`invert_clearerror@`	Clears error state

Creation & Destruction

Function	Signature	Description
`invert#(parent#)`	`invert#@#`	Creates invert effect on parent. Returns effect pointer. Effect is enabled by default.
`invert_free(effect#)`	`invert_free@#`	Destroys effect, removes from parent

Effect Control

Function	Signature	Description
`invert_enabled#(effect#, value)`	`invert_enabled#@#n`	Enables (1) or disables (0) inversion
`invert_enabled(effect#)`	`invert_enabled@#`	Gets enabled state
`invert_trigger#(effect#, trigger$)`	`invert_trigger#@#$`	Sets trigger (e.g. `"IsMouseOver=true"`)
`invert_trigger$(effect#)`	`invert_trigger$@#`	Gets trigger string

Complete Examples

Toggle Invert

╯ invert-toggle.bas─◻✕
let frm# = Pointer#(0)
let rect# = Pointer#(0)
let fx# = Pointer#(0)

frm# = form#("Invert Demo", 400, 300)

rect# = rectangle#(frm#)
rectangle_bounds#(rect#, 50, 50, 200, 100)
rectangle_fill#(rect#, "Red")

fx# = invert#(rect#)
invert_enabled#(fx#, 0)  ' Start with original

let btn# = button#(frm#, "Toggle Invert")
button_bounds#(btn#, 50, 180, 120, 30)
button_onclick#(btn#, "ToggleInvert")

form_show(frm#)

function ToggleInvert(sender#) local e
  e = invert_enabled(fx#)
  if e = 1 then
    invert_enabled#(fx#, 0)
  else
    invert_enabled#(fx#, 1)
  endif
endfunction

Hover-Based Inversion

╯ invert-hover.bas─◻✕
let frm# = form#("Hover Invert", 450, 280)

' Three cards that invert on hover
CreateInvertCard(frm#, 50, 70, "Red", "Card 1")
CreateInvertCard(frm#, 175, 70, "Green", "Card 2")
CreateInvertCard(frm#, 300, 70, "Blue", "Card 3")

let info# = label#(frm#, "Hover over cards to invert", 120, 30)

form_show(frm#)

function CreateInvertCard(parent#, x, y, color$, text$) local rect#, lbl#, fx#
  rect# = rectangle#(parent#)
  rectangle_bounds#(rect#, x, y, 100, 120)
  rectangle_fill#(rect#, color$)
  rectangle_corners#(rect#, 6, 6)

  lbl# = label#(rect#, text$, 25, 50)
  label_fontcolor#(lbl#, "White")
  label_hittest#(lbl#, 0)

  fx# = invert#(rect#)
  invert_trigger#(fx#, "IsMouseOver=true")
endfunction

Inversion Gallery

╯ invert-gallery.bas─◻✕
let frm# = form#("Inversion Gallery", 500, 300)

' Original colours
let r1# = rectangle#(frm#)
rectangle_bounds#(r1#, 40, 60, 100, 80)
rectangle_fill#(r1#, "Red")
let l1# = label#(frm#, "Red", 70, 150)

let r2# = rectangle#(frm#)
rectangle_bounds#(r2#, 200, 60, 100, 80)
rectangle_fill#(r2#, "Green")
let l2# = label#(frm#, "Green", 225, 150)

let r3# = rectangle#(frm#)
rectangle_bounds#(r3#, 360, 60, 100, 80)
rectangle_fill#(r3#, "Blue")
let l3# = label#(frm#, "Blue", 390, 150)

' Inverted versions
let ri1# = rectangle#(frm#)
rectangle_bounds#(ri1#, 40, 180, 100, 80)
rectangle_fill#(ri1#, "Red")
let fx1# = invert#(ri1#)
let li1# = label#(frm#, "Cyan", 65, 268)

let ri2# = rectangle#(frm#)
rectangle_bounds#(ri2#, 200, 180, 100, 80)
rectangle_fill#(ri2#, "Green")
let fx2# = invert#(ri2#)
let li2# = label#(frm#, "Magenta", 218, 268)

let ri3# = rectangle#(frm#)
rectangle_bounds#(ri3#, 360, 180, 100, 80)
rectangle_fill#(ri3#, "Blue")
let fx3# = invert#(ri3#)
let li3# = label#(frm#, "Yellow", 385, 268)

let title# = label#(frm#, "Original vs Inverted", 170, 20)

form_show(frm#)

Best Practices

Practice	Why
Use trigger for hover inversion	`"IsMouseOver=true"` gives instant visual feedback
Start disabled for toggle patterns	`invert_enabled#(fx#, 0)` lets user activate on demand
Works on images too	Creates dramatic photographic negative effect on photos
Combine with other effects	Invert + HueAdjust + Contrast for creative colour grading
Use for dark/light mode toggle	Quick “inverted” view of interface panels
Remember double-invert = original	Inverting twice returns to the exact original
Use `label_hittest#(lbl#, 0)`	Prevents labels from stealing hover events on inverted cards

Quick Reference

Function	Signature	Description
ERROR HANDLING
`invert_error()`	`invert_error@`	Last error code
`invert_errormsg$()`	`invert_errormsg$@`	Last error message
`invert_strerror$(code)`	`invert_strerror$@n`	Error code to text
`invert_clearerror()`	`invert_clearerror@`	Clear error state
CREATION & DESTRUCTION
`invert#(parent#)`	`invert#@#`	Create invert effect on control
`invert_free(effect#)`	`invert_free@#`	Destroy effect
EFFECT CONTROL
`invert_enabled#(e#, val)`	`invert_enabled#@#n`	Enable (1) / disable (0)
`invert_enabled(e#)`	`invert_enabled@#`	Get enabled state
`invert_trigger#(e#, str$)`	`invert_trigger#@#$`	Set trigger string
`invert_trigger$(e#)`	`invert_trigger$@#`	Get trigger string

10 functions. Part of the Plan9Basic visual effects library system.