tga.go

package tga

type rawHeader struct {
	IdLength      uint8
	PaletteType   uint8
	ImageType     uint8
	PaletteFirst  uint16
	PaletteLength uint16
	PaletteBPP    uint8
	OriginX       uint16
	OriginY       uint16
	Width         uint16
	Height        uint16
	BPP           uint8
	Flags         uint8
}

type rawFooter struct {
	ExtAreaOffset uint32
	DevDirOffset  uint32
	Signature     [18]byte // tgaSignature
}

const (
	flagOriginRight   = 1 << 4
	flagOriginTop     = 1 << 5
	flagAlphaSizeMask = 0x0f
)

const (
	imageTypePaletted   = 1
	imageTypeTrueColor  = 2
	imageTypeMonoChrome = 3
	imageTypeMask       = 3
	imageTypeFlagRLE    = 1 << 3
)

const (
	tgaRawHeaderSize = 18
	tgaRawFooterSize = 26
)

const (
	extAreaAttrTypeOffset = 0x1ee
)

const (
	attrTypeAlpha              = 3
	attrTypePremultipliedAlpha = 4
)

var tgaSignature = []byte("TRUEVISION-XFILE.\x00")

func newFooter() *rawFooter {
	f := &rawFooter{}
	copy(f.Signature[:], tgaSignature)
	return f
}

func newExtArea(attrType byte) []byte {
	area := make([]byte, extAreaAttrTypeOffset+1)
	area[0], area[1] = 0xef, 0x01 // size
	area[extAreaAttrTypeOffset] = attrType
	return area
}