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colormap.go
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colormap.go
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package xwd
import (
"encoding/binary"
"image/color"
"io"
)
// Color is a color in the xwd image.
type Color struct {
Pixel uint32
Red uint16
Green uint16
Blue uint16
Flags uint8
Padding uint8
}
const colorSize = 4 + 2 + 2 + 2 + 1 + 1
// RGBA implements the image/color.Color.RGBA() method.
// It returns rgb values in between 0 and 0xffff and an alpha value of 0xffff.
func (c *Color) RGBA() (r, g, b, a uint32) {
return uint32(c.Red), uint32(c.Green), uint32(c.Blue), uint32(color.Opaque.A)
}
type ColorMap []Color
const colormapKeySize = 1 // uint8, this is the size in the pixmap, not in the colormap
func (c *ColorMap) Get(i int) Color {
return (*c)[i]
}
// ReadColorMap reads the colormap from an xwd image, provided that the header has already been read
// and discarded from the reader.
// It returns the color map or any encountered error.
func ReadColorMap(r io.Reader, h *FileHeader) (ColorMap, error) {
var m ColorMap = make([]Color, h.NumberOfColors)
// Use NumOfColors instead of ColorMapEntries: https://gitlab.freedesktop.org/xorg/app/xwd/-/blob/master/xwd.c#L489
var i uint32
var err error
buf := make([]byte, colorSize)
for i = 0; i < h.ColorMapEntries; i++ {
_, err = r.Read(buf)
if err != nil {
return nil, &IOError{err, "reading colormap"}
}
m[i] = Color{
binary.BigEndian.Uint32(buf[0:4]), // << 8 seems to be wrong
binary.BigEndian.Uint16(buf[4:6]),
binary.BigEndian.Uint16(buf[6:8]),
binary.BigEndian.Uint16(buf[8:10]),
buf[10], buf[11],
}
}
return m, nil
}