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scaling the palette working on third attempt 

See commits b4e997adb8 and 2777479a94. This seems like a good sign that
dithering is now extremely precise.
This commit is contained in:
Kartik K. Agaram 2021-07-13 17:05:28 -07:00
parent 272432ce75
commit 169e021cc3
1 changed files with 16 additions and 2 deletions
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18
img.mu
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@ -17,6 +17,7 @@ type image {
# 1: portable bitmap (P1) - pixels 0 or 1
# 2: portable greymap (P2) - pixels 1-byte greyscale values
# 3: portable pixmap (P3) - pixels 3-byte rgb values
max: int
width: int
height: int
data: (handle array byte)
@ -253,8 +254,10 @@ fn initialize-image-from-pgm _self: (addr image), in: (addr stream byte) {
break-if-=
draw-text-wrapping-right-then-down-from-cursor-over-full-screen 0/screen, "levels of grey is not 255; continuing and hoping for the best", 0x2b/fg 0/bg
}
var dest/edi: (addr int) <- get self, max
copy-to *dest, tmp
# save width, height
var dest/edi: (addr int) <- get self, width
dest <- get self, width
copy-to *dest, width
dest <- get self, height
copy-to *dest, height
@ -444,6 +447,12 @@ fn dither-pgm-unordered _src: (addr image), _dest: (addr image) {
var dest-height-a/ecx: (addr int) <- get dest, height
copy-to *dest-height-a, tmp
}
# compute scaling factor 255/max
var target-scale/eax: int <- copy 0xff
var scale-f/xmm7: float <- convert target-scale
var src-max-a/eax: (addr int) <- get src, max
var tmp-f/xmm0: float <- convert *src-max-a
scale-f <- divide tmp-f
# transform 'data'
var capacity/ebx: int <- copy src-width
capacity <- multiply src-height
@ -467,10 +476,15 @@ fn dither-pgm-unordered _src: (addr image), _dest: (addr image) {
compare x, src-width
break-if->=
var initial-color/eax: byte <- _read-pgm-buffer src-data, x, y, src-width
# . scale to 255 levels
var initial-color-int/eax: int <- copy initial-color
var initial-color-f/xmm0: float <- convert initial-color-int
initial-color-f <- multiply scale-f
initial-color-int <- convert initial-color-f
var error/esi: int <- _read-dithering-error errors, x, y, src-width
# error += (initial-color << 16)
{
var tmp/eax: int <- copy initial-color
var tmp/eax: int <- copy initial-color-int
tmp <- shift-left 0x10 # we have 32 bits; we'll use 16 bits for the fraction and leave 8 for unanticipated overflow
error <- add tmp
}