nori/palette.go

package nori

import (
	"encoding/binary"
	"fmt"
	"image/color"
	"io"
)

type PaletteSection struct {
	Version          uint32
	Params           [4]uint32
	OpaqueIndexCount uint32
	DataLength       uint32
	Palette          [256]*color.RGBA
	MainBounds       [2]uint32

	lastSignature [4]byte
}

func (p *PaletteSection) Decode(rd io.Reader) error {
	if _, err := io.ReadFull(rd, p.lastSignature[:]); err != nil {
		return err
	}
	if sig, target := string(p.lastSignature[:]), "PAL_"; sig != target {
		return fmt.Errorf("bad sig: want %s, got %s", target, sig)
	}
	p.Palette = [256]*color.RGBA{}
	if err := binary.Read(rd, end, &p.Version); err != nil {
		return err
	}
	if err := binary.Read(rd, end, p.Params[:]); err != nil {
		return err
	}
	if err := binary.Read(rd, end, &p.OpaqueIndexCount); err != nil {
		return err
	}
	if err := binary.Read(rd, end, &p.DataLength); err != nil {
		return err
	}
	for i := 0; i < 256; i++ {
		rgb := [3]byte{}
		_, err := io.ReadFull(rd, rgb[:])
		if err != nil {
			return err
		}
		alpha := uint8(0xff)
		if rgb[0] == 0x00 && rgb[1] == 0xff && rgb[2] == 0x00 {
			alpha = 0x00
		}
		if rgb[0] == 0xff && rgb[1] == 0x00 && rgb[2] == 0xff {
			alpha = 0x00
		}
		p.Palette[i] = &color.RGBA{
			rgb[0], rgb[1], rgb[2],
			alpha,
		}
	}
	// NOTE: for some reason, the images do not render right if the first pallette colour alpha is not set to 0
	p.setBoard(0, 0, 0)

	for i := uint32(0); i < p.OpaqueIndexCount; i++ {
		var first uint32
		if err := binary.Read(rd, end, &first); err != nil {
			return err
		}

		var last uint32
		if err := binary.Read(rd, end, &last); err != nil {
			return err
		}
		//log.Println("oic", p.OpaqueIndexCount, i, first, last)
		// TODO: figure out what setBoard actually does
		//p.setBoard(first, last, 255)
	}
	return nil
}

func (p *PaletteSection) setBoard(start uint32, end uint32, alpha int32) {
	if !(start >= 0 && end >= 0 && start < 256 && end < 256) {
		return
	}

	for i := start; i <= end; i++ {
		p.Palette[i].A = uint8(alpha)
	}
}