115 lines
3.1 KiB
Go
115 lines
3.1 KiB
Go
// image_dib.go 将 Windows 剪贴板的 CF_DIB（BITMAPINFO + 像素）转换为 PNG。
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//
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// 剪贴板截图类内容常见两种来源：现代应用直接提供 "PNG" 注册格式；老应用
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// （如 Server 上的画图）只提供 CF_DIB。本转换器覆盖最常见子集：
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// BI_RGB / BI_BITFIELDS 压缩、24/32bpp、底行优先（默认）与 top-down。
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package cliprdr
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import (
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"bytes"
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"encoding/binary"
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"fmt"
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"image"
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"image/png"
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)
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// DIBToPNG 把 CF_DIB 数据解码并编码为 PNG；不支持的子集返回错误。
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func DIBToPNG(dib []byte) ([]byte, error) {
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if len(dib) < 40 {
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return nil, fmt.Errorf("dib too short: %d", len(dib))
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}
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biSize := binary.LittleEndian.Uint32(dib[0:4])
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w := int(int32(binary.LittleEndian.Uint32(dib[4:8])))
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hRaw := int32(binary.LittleEndian.Uint32(dib[8:12]))
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topDown := hRaw < 0
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h := int(hRaw)
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if h < 0 {
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h = -h
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}
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bpp := binary.LittleEndian.Uint16(dib[14:16])
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compression := binary.LittleEndian.Uint32(dib[16:20])
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if w <= 0 || h <= 0 || w > 16384 || h > 16384 {
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return nil, fmt.Errorf("bad dimensions %dx%d", w, h)
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}
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var rMask, gMask, bMask uint32
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pixOff := int(biSize)
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switch compression {
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case 0: // BI_RGB
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rMask, gMask, bMask = 0x00FF0000, 0x0000FF00, 0x000000FF
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case 3: // BI_BITFIELDS
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if biSize >= 108 { // BITMAPV4HEADER/V5HEADER 内含掩码
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rMask = binary.LittleEndian.Uint32(dib[40:44])
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gMask = binary.LittleEndian.Uint32(dib[44:48])
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bMask = binary.LittleEndian.Uint32(dib[48:52])
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} else { // 三个 DWORD 掩码紧跟标准头
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if pixOff+12 > len(dib) {
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return nil, fmt.Errorf("missing bitfields masks")
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}
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rMask = binary.LittleEndian.Uint32(dib[pixOff:])
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gMask = binary.LittleEndian.Uint32(dib[pixOff+4:])
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bMask = binary.LittleEndian.Uint32(dib[pixOff+8:])
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pixOff += 12
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}
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default:
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return nil, fmt.Errorf("unsupported compression %d", compression)
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}
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if bpp != 24 && bpp != 32 {
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return nil, fmt.Errorf("unsupported bpp %d", bpp)
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}
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stride := (w*int(bpp) + 31) / 32 * 4
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if pixOff+stride*h > len(dib) {
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return nil, fmt.Errorf("dib truncated: need %d, have %d", pixOff+stride*h, len(dib))
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}
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img := image.NewRGBA(image.Rect(0, 0, w, h))
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for y := 0; y < h; y++ {
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srcY := y
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if !topDown {
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srcY = h - 1 - y
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}
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row := dib[pixOff+srcY*stride:]
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for x := 0; x < w; x++ {
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var r8, g8, b8 uint8
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if bpp == 32 {
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v := binary.LittleEndian.Uint32(row[x*4:])
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r8, g8, b8 = maskTo8(v, rMask), maskTo8(v, gMask), maskTo8(v, bMask)
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} else {
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o := x * 3
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b8, g8, r8 = row[o], row[o+1], row[o+2]
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}
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i := img.PixOffset(x, y)
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img.Pix[i], img.Pix[i+1], img.Pix[i+2], img.Pix[i+3] = r8, g8, b8, 255
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}
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}
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var buf bytes.Buffer
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if err := png.Encode(&buf, img); err != nil {
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return nil, err
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}
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return buf.Bytes(), nil
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}
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// maskTo8 把 mask 提取出的位域缩放为 8 位
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func maskTo8(v, mask uint32) uint8 {
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if mask == 0 {
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return 0
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}
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shift := 0
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for mask&1 == 0 {
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mask >>= 1
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shift++
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}
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bits := 0
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for mask != 0 {
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mask >>= 1
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bits++
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}
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val := (v >> uint(shift)) & ((1 << uint(bits)) - 1)
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if bits < 8 {
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return uint8(val<<(8-bits) | val>>(2*uint(bits)-8))
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}
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return uint8(val >> uint(bits-8))
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}
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