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@ -8,6 +8,7 @@ package models |
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import ( |
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"fmt" |
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"html/template" |
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"math" |
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"regexp" |
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"strconv" |
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"strings" |
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@ -138,19 +139,44 @@ func (label *Label) BelongsToRepo() bool { |
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return label.RepoID > 0 |
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} |
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// SrgbToLinear converts a component of an sRGB color to its linear intensity
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// See: https://en.wikipedia.org/wiki/SRGB#The_reverse_transformation_(sRGB_to_CIE_XYZ)
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func SrgbToLinear(color uint8) float64 { |
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flt := float64(color) / 255 |
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if flt <= 0.04045 { |
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return flt / 12.92 |
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} |
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return math.Pow((flt+0.055)/1.055, 2.4) |
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} |
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// Luminance returns the luminance of an sRGB color
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func Luminance(color uint32) float64 { |
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r := SrgbToLinear(uint8(0xFF & (color >> 16))) |
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g := SrgbToLinear(uint8(0xFF & (color >> 8))) |
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b := SrgbToLinear(uint8(0xFF & color)) |
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// luminance ratios for sRGB
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return 0.2126*r + 0.7152*g + 0.0722*b |
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} |
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// LuminanceThreshold is the luminance at which white and black appear to have the same contrast
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// i.e. x such that 1.05 / (x + 0.05) = (x + 0.05) / 0.05
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// i.e. math.Sqrt(1.05*0.05) - 0.05
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const LuminanceThreshold float64 = 0.179 |
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// ForegroundColor calculates the text color for labels based
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// on their background color.
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func (label *Label) ForegroundColor() template.CSS { |
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if strings.HasPrefix(label.Color, "#") { |
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if color, err := strconv.ParseUint(label.Color[1:], 16, 64); err == nil { |
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r := float32(0xFF & (color >> 16)) |
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g := float32(0xFF & (color >> 8)) |
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b := float32(0xFF & color) |
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luminance := (0.2126*r + 0.7152*g + 0.0722*b) / 255 |
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// NOTE: see web_src/js/components/ContextPopup.vue for similar implementation
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luminance := Luminance(uint32(color)) |
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if luminance < 0.66 { |
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// prefer white or black based upon contrast
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if luminance < LuminanceThreshold { |
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return template.CSS("#fff") |
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} |
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return template.CSS("#000") |
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} |
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} |
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