limage - grayalpha.go

     1  package limage
     2  
     3  import (
     4  	"image"
     5  	"image/color"
     6  
     7  	"vimagination.zapto.org/limage/lcolor"
     8  )
     9  
    10  // GrayAlpha is an image of GrayAlpha pixels
    11  type GrayAlpha struct {
    12  	Pix    []lcolor.GrayAlpha
    13  	Stride int
    14  	Rect   image.Rectangle
    15  }
    16  
    17  // NewGrayAlpha create a new GrayAlpha image with the given bounds
    18  func NewGrayAlpha(r image.Rectangle) *GrayAlpha {
    19  	w, h := r.Dx(), r.Dy()
    20  	return &GrayAlpha{
    21  		Pix:    make([]lcolor.GrayAlpha, w*h),
    22  		Stride: w,
    23  		Rect:   r,
    24  	}
    25  }
    26  
    27  // At returns the color for the pixel at the specified coords
    28  func (g *GrayAlpha) At(x, y int) color.Color {
    29  	return g.GrayAlphaAt(x, y)
    30  }
    31  
    32  // Bounds returns the limits of the image
    33  func (g *GrayAlpha) Bounds() image.Rectangle {
    34  	return g.Rect
    35  }
    36  
    37  // ColorModel returns a color model to transform arbitrary colours into a
    38  // GrayAlpha color
    39  func (g *GrayAlpha) ColorModel() color.Model {
    40  	return lcolor.GrayAlphaModel
    41  }
    42  
    43  // GrayAlphaAt returns a GrayAlpha colr for the specified coords
    44  func (g *GrayAlpha) GrayAlphaAt(x, y int) lcolor.GrayAlpha {
    45  	if !(image.Point{x, y}.In(g.Rect)) {
    46  		return lcolor.GrayAlpha{}
    47  	}
    48  	return g.Pix[g.PixOffset(x, y)]
    49  }
    50  
    51  // Opaque returns true if all pixels have full alpha
    52  func (g *GrayAlpha) Opaque() bool {
    53  	for _, c := range g.Pix {
    54  		if c.A != 255 {
    55  			return false
    56  		}
    57  	}
    58  	return true
    59  }
    60  
    61  // PixOffset returns the index of the element of Pix corresponding to the given
    62  // coords
    63  func (g *GrayAlpha) PixOffset(x, y int) int {
    64  	return (y-g.Rect.Min.Y)*g.Stride + x - g.Rect.Min.X
    65  }
    66  
    67  // Set converts the given colour to a GrayAlpha colour and sets it at the given
    68  // coords
    69  func (g *GrayAlpha) Set(x, y int, c color.Color) {
    70  	if !(image.Point{x, y}.In(g.Rect)) {
    71  		return
    72  	}
    73  	g.Pix[g.PixOffset(x, y)] = lcolor.GrayAlphaModel.Convert(c).(lcolor.GrayAlpha)
    74  }
    75  
    76  // SetGrayAlpha sets the colour at the given coords
    77  func (g *GrayAlpha) SetGrayAlpha(x, y int, ga lcolor.GrayAlpha) {
    78  	if !(image.Point{x, y}.In(g.Rect)) {
    79  		return
    80  	}
    81  	g.Pix[g.PixOffset(x, y)] = ga
    82  }
    83  
    84  // SubImage retuns the Image viewable through the given bounds
    85  func (g *GrayAlpha) SubImage(r image.Rectangle) image.Image {
    86  	r = r.Intersect(g.Rect)
    87  	if r.Empty() {
    88  		return &GrayAlpha{}
    89  	}
    90  	return &GrayAlpha{
    91  		Pix:    g.Pix[g.PixOffset(r.Min.X, r.Min.Y):],
    92  		Stride: g.Stride,
    93  		Rect:   r,
    94  	}
    95  }
    96