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Diffstat (limited to 'hsl.go')
| -rw-r--r-- | hsl.go | 139 |
1 files changed, 139 insertions, 0 deletions
@@ -0,0 +1,139 @@ +// Copyright (c) 2012 Rodrigo Moraes. All rights reserved. +// +// Redistribution and use in source and binary forms, with or without +// modification, are permitted provided that the following conditions are +// met: +// +// * Redistributions of source code must retain the above copyright +// notice, this list of conditions and the following disclaimer. +// * Redistributions in binary form must reproduce the above +// copyright notice, this list of conditions and the following disclaimer +// in the documentation and/or other materials provided with the +// distribution. +// * Neither the name of Google Inc. nor the names of its +// contributors may be used to endorse or promote products derived from +// this software without specific prior written permission. +// +// THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS +// "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT +// LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR +// A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT +// OWNER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, +// SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT +// LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, +// DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY +// THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT +// (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE +// OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE. + +package excelize + +import ( + "image/color" + "math" +) + +// HSLModel converts any color.Color to a HSL color. +var HSLModel = color.ModelFunc(hslModel) + +// HSL represents a cylindrical coordinate of points in an RGB color model. +// +// Values are in the range 0 to 1. +type HSL struct { + H, S, L float64 +} + +// RGBA returns the alpha-premultiplied red, green, blue and alpha values +// for the HSL. +func (c HSL) RGBA() (uint32, uint32, uint32, uint32) { + r, g, b := HSLToRGB(c.H, c.S, c.L) + return uint32(r) * 0x101, uint32(g) * 0x101, uint32(b) * 0x101, 0xffff +} + +// hslModel converts a color.Color to HSL. +func hslModel(c color.Color) color.Color { + if _, ok := c.(HSL); ok { + return c + } + r, g, b, _ := c.RGBA() + h, s, l := RGBToHSL(uint8(r>>8), uint8(g>>8), uint8(b>>8)) + return HSL{h, s, l} +} + +// RGBToHSL converts an RGB triple to a HSL triple. +func RGBToHSL(r, g, b uint8) (h, s, l float64) { + fR := float64(r) / 255 + fG := float64(g) / 255 + fB := float64(b) / 255 + max := math.Max(math.Max(fR, fG), fB) + min := math.Min(math.Min(fR, fG), fB) + l = (max + min) / 2 + if max == min { + // Achromatic. + h, s = 0, 0 + } else { + // Chromatic. + d := max - min + if l > 0.5 { + s = d / (2.0 - max - min) + } else { + s = d / (max + min) + } + switch max { + case fR: + h = (fG - fB) / d + if fG < fB { + h += 6 + } + case fG: + h = (fB-fR)/d + 2 + case fB: + h = (fR-fG)/d + 4 + } + h /= 6 + } + return +} + +// HSLToRGB converts an HSL triple to a RGB triple. +func HSLToRGB(h, s, l float64) (r, g, b uint8) { + var fR, fG, fB float64 + if s == 0 { + fR, fG, fB = l, l, l + } else { + var q float64 + if l < 0.5 { + q = l * (1 + s) + } else { + q = l + s - s*l + } + p := 2*l - q + fR = hueToRGB(p, q, h+1.0/3) + fG = hueToRGB(p, q, h) + fB = hueToRGB(p, q, h-1.0/3) + } + r = uint8((fR * 255) + 0.5) + g = uint8((fG * 255) + 0.5) + b = uint8((fB * 255) + 0.5) + return +} + +// hueToRGB is a helper function for HSLToRGB. +func hueToRGB(p, q, t float64) float64 { + if t < 0 { + t++ + } + if t > 1 { + t-- + } + if t < 1.0/6 { + return p + (q-p)*6*t + } + if t < 0.5 { + return q + } + if t < 2.0/3 { + return p + (q-p)*(2.0/3-t)*6 + } + return p +} |