140 lines
3.6 KiB
Go
140 lines
3.6 KiB
Go
// Copyright (c) 2012 Rodrigo Moraes. All rights reserved.
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//
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// Redistribution and use in source and binary forms, with or without
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// modification, are permitted provided that the following conditions are
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// met:
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//
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// * Redistributions of source code must retain the above copyright
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// notice, this list of conditions and the following disclaimer.
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// * Redistributions in binary form must reproduce the above
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// copyright notice, this list of conditions and the following disclaimer
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// in the documentation and/or other materials provided with the
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// distribution.
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// * Neither the name of Google Inc. nor the names of its
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// contributors may be used to endorse or promote products derived from
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// this software without specific prior written permission.
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//
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// THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
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// "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
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// LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR
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// A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT
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// OWNER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL,
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// SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT
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// LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE,
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// DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY
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// THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
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// (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE
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// OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
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package excelize
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import (
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"image/color"
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"math"
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)
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// HSLModel converts any color.Color to a HSL color.
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var HSLModel = color.ModelFunc(hslModel)
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// HSL represents a cylindrical coordinate of points in an RGB color model.
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//
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// Values are in the range 0 to 1.
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type HSL struct {
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H, S, L float64
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}
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// RGBA returns the alpha-premultiplied red, green, blue and alpha values
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// for the HSL.
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func (c HSL) RGBA() (uint32, uint32, uint32, uint32) {
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r, g, b := HSLToRGB(c.H, c.S, c.L)
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return uint32(r) * 0x101, uint32(g) * 0x101, uint32(b) * 0x101, 0xffff
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}
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// hslModel converts a color.Color to HSL.
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func hslModel(c color.Color) color.Color {
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if _, ok := c.(HSL); ok {
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return c
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}
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r, g, b, _ := c.RGBA()
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h, s, l := RGBToHSL(uint8(r>>8), uint8(g>>8), uint8(b>>8))
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return HSL{h, s, l}
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}
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// RGBToHSL converts an RGB triple to an HSL triple.
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func RGBToHSL(r, g, b uint8) (h, s, l float64) {
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fR := float64(r) / 255
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fG := float64(g) / 255
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fB := float64(b) / 255
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max := math.Max(math.Max(fR, fG), fB)
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min := math.Min(math.Min(fR, fG), fB)
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l = (max + min) / 2
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if max == min {
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// Achromatic.
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h, s = 0, 0
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} else {
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// Chromatic.
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d := max - min
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if l > 0.5 {
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s = d / (2.0 - max - min)
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} else {
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s = d / (max + min)
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}
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switch max {
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case fR:
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h = (fG - fB) / d
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if fG < fB {
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h += 6
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}
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case fG:
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h = (fB-fR)/d + 2
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case fB:
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h = (fR-fG)/d + 4
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}
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h /= 6
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}
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return
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}
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// HSLToRGB converts an HSL triple to an RGB triple.
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func HSLToRGB(h, s, l float64) (r, g, b uint8) {
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var fR, fG, fB float64
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if s == 0 {
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fR, fG, fB = l, l, l
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} else {
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var q float64
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if l < 0.5 {
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q = l * (1 + s)
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} else {
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q = l + s - s*l
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}
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p := 2*l - q
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fR = hueToRGB(p, q, h+1.0/3)
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fG = hueToRGB(p, q, h)
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fB = hueToRGB(p, q, h-1.0/3)
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}
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r = uint8((fR * 255) + 0.5)
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g = uint8((fG * 255) + 0.5)
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b = uint8((fB * 255) + 0.5)
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return
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}
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// hueToRGB is a helper function for HSLToRGB.
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func hueToRGB(p, q, t float64) float64 {
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if t < 0 {
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t++
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}
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if t > 1 {
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t--
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}
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if t < 1.0/6 {
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return p + (q-p)*6*t
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}
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if t < 0.5 {
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return q
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}
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if t < 2.0/3 {
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return p + (q-p)*(2.0/3-t)*6
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}
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return p
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}
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