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|
type mode =
| Normal | Multiply | Screen | Overlay (* | SoftLight | HardLight *)
| ColorDodge | ColorBurn | Darken | Lighten | Difference
| Exclusion (* | Luminosity | Color | Saturation | Hue *)
;;
(* look at gxblend.c of ghostscript *)
let blend =
function
| Normal -> fun src dst -> src
| Multiply ->
fun src dst ->
let t = dst * src + 0x80 in
let t = t + t lsr 8 in
t lsr 8
| Screen ->
fun src dst ->
let t = (0xff - dst) * (0xff - src) + 0x80 in
let t = t + t lsr 8 in
0xff - t lsr 8
| Overlay ->
fun src dst ->
let t =
if dst < 0x80 then 2 * dst * src
else 0xf301 - 2 * (0xff - dst) * (0xff - src) in
let t = t + 0x80 in
let t = t + t lsr 8 in
t lsr 8
(*
| SoftLight ->
if s < 0x80 then begin
let t = (0xff - (src lsl 1)) * art_blend_sq_diff_8[dst] in
let t = t + 0x8000 in
dst - t lsr 16
end else begin
let t = ((src lsl 1) - 0xff) * art_blend_soft_light_8[dst] in
let t = t + 0x80 in
let t = t + t lsr 8 in
dst + t lsr 8
end
*)
| ColorDodge ->
fun src dst ->
if dst = 0 then 0 else if dst >= src then 0xff
else (0x1fe * dst + src) / (src lsl 1)
| ColorBurn ->
fun src dst ->
let dst = 0xff - dst in
if dst = 0 then 0xff else if dst >= src then 0
else 0xff - (0x1fe * dst + src) / (src lsl 1)
| Darken ->
fun src dst -> if dst < src then dst else src
| Lighten ->
fun src dst -> if dst > src then dst else src
| Difference ->
fun src dst ->
let t = dst - src in
if t < 0 then -t else t
| Exclusion ->
fun src dst ->
let t = (0xff - dst) * src + dst * (0xff - src) in
let t = t + 0x80 in
let t = t + t lsr 8 in
t lsr 8
| _ -> assert false
;;
open Color
let f blendmode srcalpha =
let blender = blend blendmode in
match srcalpha with
| 0 -> fun src dst -> dst
| 255 ->
fun src dst ->
{r= blender src.r dst.r;
g= blender src.g dst.g;
b= blender src.b dst.b}
| _ ->
let a' = 255 - srcalpha in
fun src dst ->
{r= (blender src.r dst.r * srcalpha + dst.r * a') / 255;
g= (blender src.g dst.g * srcalpha + dst.g * a') / 255;
b= (blender src.b dst.b * srcalpha + dst.b * a') / 255 }
;;
|
