1 files changed, 80 insertions, 0 deletions
diff --git a/subprojects/pixpat/pixpat-native/src/io/csi2.h b/subprojects/pixpat/pixpat-native/src/io/csi2.h
new file mode 100644
index 0000000..59a8f8d
--- /dev/null
+++ b/subprojects/pixpat/pixpat-native/src/io/csi2.h
@@ -0,0 +1,80 @@
+#pragma once
+
+// Shared MIPI CSI-2 byte (un)packing for the 10P / 12P forms used by
+// Bayer raw and Y-only grayscale.
+//
+//   10P: 4 samples in 5 bytes — bytes 0..3 hold the high 8 bits of
+//        samples 0..3; byte 4 holds 4 x 2 LSBs (sample 0 in bits 6..7,
+//        sample 1 in bits 4..5, ...).
+//   12P: 2 samples in 3 bytes — bytes 0..1 hold the high 8 bits of
+//        samples 0..1; byte 2 holds 2 x 4 LSBs (sample 0 in bits 4..7,
+//        sample 1 in bits 0..3).
+//
+// Helpers deal in the stored integer (low BitDepth bits set);
+// normalization to/from the 16-bit pivot stays in the caller.
+
+#include <array>
+#include <cstddef>
+#include <cstdint>
+
+namespace pixpat::detail::csi2
+{
+
+template <size_t BitDepth>
+struct packed_traits;
+
+template <>
+struct packed_traits<10> {
+	static constexpr size_t ppg = 4;
+	static constexpr size_t bpg = 5;
+};
+
+template <>
+struct packed_traits<12> {
+	static constexpr size_t ppg = 2;
+	static constexpr size_t bpg = 3;
+};
+
+// Extract one BitDepth-bit sample from a packed group, where `i` is the
+// in-group index (0..ppg-1). The returned value occupies the low
+// BitDepth bits.
+template <size_t BitDepth>
+inline uint16_t unpack_sample(const uint8_t* src, size_t i) noexcept
+{
+	if constexpr (BitDepth == 10) {
+		const uint8_t hi  = src[i];
+		const uint8_t lsb = (src[4] >> ((3 - i) * 2)) & 0x03;
+		return uint16_t((hi << 2) | lsb);
+	} else { // 12
+		const uint8_t hi  = src[i];
+		const uint8_t lsb = (i == 0) ? ((src[2] >> 4) & 0x0F)
+		                             :  (src[2]       & 0x0F);
+		return uint16_t((hi << 4) | lsb);
+	}
+}
+
+// Write `ppg` BitDepth-bit samples (low BitDepth bits significant) into
+// a packed group of `bpg` bytes.
+template <size_t BitDepth>
+inline void pack_group(
+	uint8_t* dst,
+	const std::array<uint16_t, packed_traits<BitDepth>::ppg>& vals) noexcept
+{
+	if constexpr (BitDepth == 10) {
+		dst[0] = (vals[0] >> 2) & 0xFF;
+		dst[1] = (vals[1] >> 2) & 0xFF;
+		dst[2] = (vals[2] >> 2) & 0xFF;
+		dst[3] = (vals[3] >> 2) & 0xFF;
+		dst[4] = ((vals[0] & 0x03) << 6)
+		         | ((vals[1] & 0x03) << 4)
+		         | ((vals[2] & 0x03) << 2)
+		         | ((vals[3] & 0x03) << 0);
+	} else { // 12
+		dst[0] = (vals[0] >> 4) & 0xFF;
+		dst[1] = (vals[1] >> 4) & 0xFF;
+		dst[2] = ((vals[0] & 0x0F) << 4)
+		         | ((vals[1] & 0x0F) << 0);
+	}
+}
+
+} // namespace pixpat::detail::csi2