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increase precision for dithering computations 

Now we get a perfect checkerboard pattern.
This commit is contained in:
Kartik K. Agaram 2021-07-10 19:56:32 -07:00
parent 3420f10f18
commit b28a31315e
1 changed files with 8 additions and 3 deletions
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@ -407,10 +407,12 @@ fn _unordered-monochrome-dither src: (addr array byte), width: int, height: int,
var error/ebx: int <- _read-buffer buf, x, y, width
$_unordered-monochrome-dither:update-error: {
var curr/eax: byte <- _read-byte-buffer src, x, y, width
error <- add curr
var curr-int/eax: int <- copy curr
curr-int <- shift-left 0x10 # we have 32 bits; we'll use 16 bits for the fraction and leave 8 for unanticipated overflow
error <- add curr-int
#? psd "e", error, 5/fg, x, y
#? draw-int32-decimal-wrapping-right-then-down-from-cursor-over-full-screen 0/screen, error, 7/fg 0/bg
compare error, 0x80
compare error, 0x800000
{
break-if->=
#? psd "p", 0, 0x14/fg, x, y
@ -419,7 +421,7 @@ fn _unordered-monochrome-dither src: (addr array byte), width: int, height: int,
}
#? psd "p", 1, 0xf/fg, x, y
_write-byte-buffer dest, x, y, width, 1/white
error <- subtract 0xff
error <- subtract 0xff0000
}
_diffuse-monochrome-dithering-errors buf, x, y, width, height, error
#? {
@ -491,6 +493,9 @@ fn psd s: (addr array byte), d: int, fg: int, x: int, y: int {
# one of pure black or white pixels.
#
# https://tannerhelland.com/2012/12/28/dithering-eleven-algorithms-source-code.html
#
# Error is currently a fixed-point number with 16-bit fraction. But
# interestingly this function doesn't care about that.
fn _diffuse-monochrome-dithering-errors buf: (addr array int), x: int, y: int, width: int, height: int, error: int {
{
compare error, 0