hsva.go

Documentation: gonum.org/v1/plot/palette

     1  // Copyright ©2015 The Gonum Authors. All rights reserved.
     2  // Use of this source code is governed by a BSD-style
     3  // license that can be found in the LICENSE file.
     4  
     5  // Copyright ©2011-2013 The bíogo Authors. All rights reserved.
     6  // Use of this source code is governed by a BSD-style
     7  // license that can be found in the LICENSE file.
     8  
     9  package palette
    10  
    11  import (
    12  	"image/color"
    13  	"math"
    14  )
    15  
    16  // HSVA represents a Hue/Saturation/Value/Alpha color.
    17  // H, S, V and A are valid within [0, 1].
    18  type HSVA struct {
    19  	H, S, V, A float64
    20  }
    21  
    22  // HSVAModel converts any color.Color to an HSVA color.
    23  var HSVAModel = color.ModelFunc(hsvaModel)
    24  
    25  func hsvaModel(c color.Color) color.Color {
    26  	if _, ok := c.(HSVA); ok {
    27  		return c
    28  	}
    29  	return rgbaToHsva(c.RGBA())
    30  }
    31  
    32  // Convert r, g, b, a to HSVA
    33  func rgbaToHsva(r, g, b, a uint32) HSVA {
    34  	red := float64(r)
    35  	blue := float64(b)
    36  	green := float64(g)
    37  
    38  	max := math.Max(red, green)
    39  	max = math.Max(max, blue)
    40  	min := math.Min(red, green)
    41  	min = math.Min(min, blue)
    42  	chroma := max - min
    43  
    44  	var hue float64
    45  	switch {
    46  	case chroma == 0:
    47  		// This should really be math.NaN() since we have a 0 length vector,
    48  		// but 0 seems to be the convention and it may simplify imports in
    49  		// dependent packages.
    50  		hue = 0
    51  	case max == red:
    52  		hue = math.Mod((green-blue)/chroma, 6)
    53  	case max == green:
    54  		hue = (blue-red)/chroma + 2
    55  	case max == blue:
    56  		hue = (red-green)/chroma + 4
    57  	}
    58  
    59  	hue /= 6
    60  
    61  	var s float64
    62  	if chroma != 0 {
    63  		s = chroma / max
    64  	}
    65  
    66  	return HSVA{
    67  		H: math.Mod(math.Mod(hue, 1)+1, 1),
    68  		S: s,
    69  		V: max / math.MaxUint16,
    70  		A: float64(a) / math.MaxUint16,
    71  	}
    72  }
    73  
    74  // RGBA allows HSVAColor to satisfy the color.Color interface.
    75  func (c HSVA) RGBA() (r, g, b, a uint32) {
    76  	var red, green, blue float64
    77  
    78  	a = uint32(math.MaxUint16 * c.A)
    79  
    80  	if c.V == 0 {
    81  		return
    82  	}
    83  
    84  	if c.S == 0 {
    85  		r, g, b = uint32(math.MaxUint16*c.V), uint32(math.MaxUint16*c.V), uint32(math.MaxUint16*c.V)
    86  		return
    87  	}
    88  
    89  	chroma := c.V * c.S
    90  	m := c.V - chroma
    91  
    92  	if !math.IsNaN(c.H) {
    93  		hue := math.Mod(c.H, 1) * 6
    94  		x := chroma * (1 - math.Abs(math.Mod(hue, 2)-1))
    95  		switch math.Floor(hue) {
    96  		case 0:
    97  			red, green = chroma, x
    98  		case 1:
    99  			red, green = x, chroma
   100  		case 2:
   101  			green, blue = chroma, x
   102  		case 3:
   103  			green, blue = x, chroma
   104  		case 4:
   105  			red, blue = x, chroma
   106  		case 5:
   107  			red, blue = chroma, x
   108  		}
   109  	} else {
   110  		red, green, blue = 0, 0, 0
   111  	}
   112  
   113  	r, g, b = uint32(math.MaxUint16*(red+m)), uint32(math.MaxUint16*(green+m)), uint32(math.MaxUint16*(blue+m))
   114  
   115  	return
   116  }
   117
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