50 lines
1.7 KiB
Common Lisp
50 lines
1.7 KiB
Common Lisp
;; Halftone/dot effect - built from primitive xector operations
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;;
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;; Uses:
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;; pool-frame - downsample to cell luminances
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;; cell-indices - which cell each pixel belongs to
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;; gather - look up cell value for each pixel
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;; local-x/y-norm - position within cell [0,1]
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;; where - conditional per-pixel
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(require-primitives "xector")
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(define-effect halftone
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:params (
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(cell-size :type int :default 12 :range [4 32] :desc "Size of halftone cells")
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(dot-scale :type float :default 0.9 :range [0.1 1.0] :desc "Max dot radius")
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(invert :type bool :default false :desc "Invert (white dots on black)")
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)
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(let* (
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;; Pool frame to get luminance per cell
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(pooled (pool-frame frame cell-size))
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(cell-lum (nth pooled 3)) ; luminance is 4th element
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;; For each output pixel, get its cell index
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(cell-idx (cell-indices frame cell-size))
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;; Get cell luminance for each pixel
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(pixel-lum (α/ (gather cell-lum cell-idx) 255))
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;; Position within cell, normalized to [-0.5, 0.5]
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(lx (α- (local-x-norm frame cell-size) 0.5))
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(ly (α- (local-y-norm frame cell-size) 0.5))
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;; Distance from cell center (0 at center, ~0.7 at corners)
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(dist (αsqrt (α+ (α² lx) (α² ly))))
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;; Radius based on luminance (brighter = bigger dot)
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(radius (α* (if invert (α- 1 pixel-lum) pixel-lum)
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(α* dot-scale 0.5)))
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;; Is this pixel inside the dot?
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(inside (α< dist radius))
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;; Output color
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(fg (if invert 255 0))
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(bg (if invert 0 255))
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(out (where inside fg bg)))
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;; Grayscale output
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(rgb out out out)))
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