Invert Function Implementation #

This document describes the implementation of the invert function for KidLisp.

Summary #

Added the missing invert function to the graphics system, with both CPU and GPU implementations. The function inverts RGB color values (255 - value) while preserving the alpha channel, following the same pattern as other image effects like contrast and brightness.

Implementation Details #

CPU Implementation (graph.mjs) #

Added invert() function that processes pixel buffer
Performs RGB inversion: RGB' = 255 - RGB
Preserves alpha channel unchanged
Supports masking for partial screen effects
Skips fully transparent pixels (optimization)
Uses performance tracking for monitoring

GPU Implementation (gpu-effects.mjs) #

Added INVERT_FRAGMENT_SHADER with simple inversion logic
Created gpuInvert() function with same signature as other GPU effects
Compiled and cached shader program and uniform locations
Follows GPU-first, CPU-fallback pattern used by other effects
Properly handles cleanup in cleanupGpuEffects()

Integration #

Exported invert from graph.mjs
Added to disk.mjs API (already present, was just calling non-existent function)
KidLisp can now call (invert) in code
Works with embedded layers and baking system (uses existing post-composite infrastructure)

Usage Examples #

KidLisp Code #

; Simple invert
(wipe "red")
(invert)
; Screen is now cyan

; Partial invert with masking
(wipe "white")
(ink "blue")
(box 50 50 100 100)
(mask 60 60 80 80)
(invert)
(unmask)
; Only the masked region is inverted

; Animation with invert
(wipe "black")
(ink "yellow")
(circle width/2 height/2 50)
(if (even frame) (invert))
; Flashing circle effect

Testing #

Created tests/invert.test.mjs with comprehensive logic tests
Verified RGB inversion formula for various colors
Tested alpha channel preservation
Confirmed double invert restores original values
Validated boundary cases

Performance #

GPU implementation provides hardware acceleration when available
CPU fallback ensures compatibility on all platforms
Transparent pixel skipping reduces unnecessary computation
Performance tracking integrated for monitoring

This implementation enables KidLisp codes like $beli (similar to $4bb but with invert) to work correctly.