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54 lines
1.8 KiB
Go
54 lines
1.8 KiB
Go
//go:build !js && !ios && !android
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package server
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import (
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"encoding/binary"
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"unsafe"
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)
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// nativeIsLittleEndian reports the byte order of the target. The word-at-a-time
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// swizzle below only holds on a little-endian layout, and the client ships
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// big-endian linux/mips and linux/mips64 builds.
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var nativeIsLittleEndian = binary.NativeEndian.Uint16([]byte{1, 0}) == 1
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// swizzleBGRAtoRGBA swaps B and R channels in a BGRA pixel buffer and copies
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// into dst in-place (dst and src may alias).
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//
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// The alpha byte is forced to 0xff so callers that capture from X11 GetImage
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// (where the X server leaves the pad byte as zero) still get an opaque image.
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func swizzleBGRAtoRGBA(dst, src []byte) {
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n := len(dst) / 4
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if len(src)/4 < n {
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n = len(src) / 4
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}
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if n == 0 {
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return
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}
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if !nativeIsLittleEndian {
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swizzleBGRAtoRGBABytes(dst[:n*4], src[:n*4])
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return
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}
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// One read-modify-write per pixel, meaningfully faster than three byte
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// stores over a whole framebuffer. The masks below describe a little-endian
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// word, so this path is guarded above rather than used unconditionally.
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dp := unsafe.Slice((*uint32)(unsafe.Pointer(&dst[0])), n)
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sp := unsafe.Slice((*uint32)(unsafe.Pointer(&src[0])), n)
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for i := range n {
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p := sp[i]
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// p in memory: B, G, R, A -> as uint32 little-endian: 0xAARRGGBB
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// Want memory: R, G, B, 0xFF -> uint32 little-endian: 0xFFBBGGRR
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dp[i] = 0xFF000000 | (p & 0x0000FF00) | ((p & 0x00FF0000) >> 16) | ((p & 0x000000FF) << 16)
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}
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}
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// swizzleBGRAtoRGBABytes is the byte-order-independent form, used on big-endian
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// targets. dst and src must be the same length and a multiple of 4.
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func swizzleBGRAtoRGBABytes(dst, src []byte) {
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for i := 0; i < len(src); i += 4 {
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b, g, r := src[i], src[i+1], src[i+2]
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dst[i], dst[i+1], dst[i+2], dst[i+3] = r, g, b, 0xFF
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}
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}
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