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let from_sRGB sRGB =
if sRGB <= 0.03928 then
sRGB /. 12.92
else
((sRGB +. 0.055) /. 1.055) ** 2.4
type rgb =
{ r: float
; g: float
; b: float
}
(* https://www.w3.org/TR/2008/REC-WCAG20-20081211/#relativeluminancedef *)
let relativeLuminance (c: rgb) =
0.2126 *. from_sRGB (c.r /. 255.) +. 0.7152 *. from_sRGB (c.g /. 255.) +. 0.0722 *. from_sRGB (c.b /. 255.)
(* https://www.w3.org/TR/2008/REC-WCAG20-20081211/#contrastratio *)
let contrast_ratio (c1: rgb) (c2: rgb) =
let rl1 = relativeLuminance c1 in
let rl2 = relativeLuminance c2 in
if (rl1 > rl2) then
(rl1 +. 0.05) /. (rl2 +. 0.05)
else
(rl2 +. 0.05) /. (rl1 +. 0.05)
let from_raw color =
let get_opt = function | Some x -> x | None -> raise (Invalid_argument "Option.get") in
let div = H.div [| HA.style ("color: " ^ color) |] [| |] in
let body = Document.query_selector_unsafe "body" in
let () = Element.append_child body div in
let rgb = [%raw {| window.getComputedStyle(div).color |}] in
let () = Element.remove_child body div in
let xs = Js.String.split ", " (get_opt (Js.String.splitByRe [%re "/[()]/"] rgb).(1)) in
{ r = Js.Float.fromString xs.(0)
; g = Js.Float.fromString xs.(1)
; b = Js.Float.fromString xs.(2)
}
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