feat(android): T-AND-004 239 字节帧编解码 + 跨端金标准向量测试
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package com.opendance.studio.model
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import java.nio.ByteBuffer
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import java.nio.ByteOrder
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/**
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* 239 字节关键点帧编解码 —— 契约 contracts/websocket-keypoints.md §2（冻结）
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*
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* 帧布局（**小端序**）：
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* ```
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* 偏移 长度 字段
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* 0 2 magic u16 = 0x4F44 ('OD')
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* 2 1 version u8 = 1
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* 3 1 flags u8 bit0 镜像 | bit1 含低置信度点 | bit2 上半身模式
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* 4 4 frame_id u32 LE，从 0 起单调递增
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* 8 231 keypoints 33 × 7B：s16 x, s16 y, s16 z, u8 conf
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* 合计 239
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* ```
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*
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* 坐标语义（contracts/skeleton-topology.md §4）：
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* x,y ∈ [0,1] 归一化图像坐标（原点左上，y 向下）；z 与 x 同尺度，
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* 负值朝向相机。归一化系数统一 **32767**。
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*
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* 本实现与 opendance-web 的 TypeScript 参考实现、opendance-windows 的 GDScript
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* 实现逐位对齐，并由单元测试用同一份金标准字节向量交叉校验。
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*/
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object KeypointFrame {
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const val MAGIC = 0x4F44
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const val PROTOCOL_VERSION = 1
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const val BINARY_SIZE = 239
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const val KEYPOINT_COUNT = 33
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const val HEADER_SIZE = 8
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const val POINT_BYTES = 7
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const val SCALE = 32767.0
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const val FLAG_MIRRORED = 1 shl 0
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const val FLAG_LOW_CONFIDENCE = 1 shl 1
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const val FLAG_UPPER_BODY_ONLY = 1 shl 2
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/** 低于该置信度的点坐标无意义，接收端必须插值 */
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const val CONFIDENCE_THRESHOLD = 0.5f
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/** 一帧姿态数据（并行数组，避免 30 FPS 循环里的对象分配） */
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class PoseFrame(
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val frameId: Int,
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val flags: Int,
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val x: FloatArray,
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val y: FloatArray,
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val z: FloatArray,
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val confidence: FloatArray,
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) {
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init {
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require(x.size == KEYPOINT_COUNT) { "x 必须为 $KEYPOINT_COUNT 项" }
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require(y.size == KEYPOINT_COUNT) { "y 必须为 $KEYPOINT_COUNT 项" }
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require(z.size == KEYPOINT_COUNT) { "z 必须为 $KEYPOINT_COUNT 项" }
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require(confidence.size == KEYPOINT_COUNT) { "confidence 必须为 $KEYPOINT_COUNT 项" }
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}
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val isMirrored: Boolean get() = (flags and FLAG_MIRRORED) != 0
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val isUpperBodyOnly: Boolean get() = (flags and FLAG_UPPER_BODY_ONLY) != 0
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val hasLowConfidence: Boolean get() = (flags and FLAG_LOW_CONFIDENCE) != 0
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/** 该点是否可用于评分 */
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fun isReliable(index: Int): Boolean = confidence[index] >= CONFIDENCE_THRESHOLD
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/** 平均置信度，用于运行页质量指示 */
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fun averageConfidence(): Float {
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var total = 0f
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for (c in confidence) total += c
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return total / confidence.size
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}
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/** 已镜像的帧需翻转 x 才能与对端坐标系一致 */
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fun xUnmirrored(index: Int): Float = if (isMirrored) 1f - x[index] else x[index]
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}
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/**
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* 校验帧字节流；合法返回 null，否则返回可读原因。
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*/
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fun validate(bytes: ByteArray): String? {
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if (bytes.size != BINARY_SIZE) {
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return "帧长度必须为 $BINARY_SIZE 字节，实际 ${bytes.size}"
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}
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val buffer = ByteBuffer.wrap(bytes).order(ByteOrder.LITTLE_ENDIAN)
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val magic = buffer.getShort(0).toInt() and 0xFFFF
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if (magic != MAGIC) {
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return "magic 校验失败：期望 0x%04X，实际 0x%04X".format(MAGIC, magic)
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}
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val version = buffer.get(2).toInt() and 0xFF
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if (version != PROTOCOL_VERSION) {
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return "不支持的协议版本 $version（本端支持 $PROTOCOL_VERSION）"
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}
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return null
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}
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/**
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* 编码为 239 字节帧 —— 本端（Android）的主要职责。
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*
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* @param xs 归一化 x，[0,1]
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* @param ys 归一化 y，[0,1]
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* @param zs 深度，约 [-1,1]，负值朝相机
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* @param confidence [0,1]
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* @param flags 见 FLAG_* 常量
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*/
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fun encode(
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frameId: Int,
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xs: FloatArray,
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ys: FloatArray,
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zs: FloatArray,
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confidence: FloatArray,
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flags: Int = 0,
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): ByteArray {
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require(xs.size == KEYPOINT_COUNT) { "xs 必须为 $KEYPOINT_COUNT 项" }
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require(ys.size == KEYPOINT_COUNT) { "ys 必须为 $KEYPOINT_COUNT 项" }
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require(zs.size == KEYPOINT_COUNT) { "zs 必须为 $KEYPOINT_COUNT 项" }
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require(confidence.size == KEYPOINT_COUNT) { "confidence 必须为 $KEYPOINT_COUNT 项" }
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val buffer = ByteBuffer.allocate(BINARY_SIZE).order(ByteOrder.LITTLE_ENDIAN)
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buffer.putShort(0, MAGIC.toShort())
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buffer.put(2, PROTOCOL_VERSION.toByte())
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buffer.put(3, (flags and 0xFF).toByte())
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buffer.putInt(4, frameId)
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for (i in 0 until KEYPOINT_COUNT) {
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val offset = HEADER_SIZE + i * POINT_BYTES
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buffer.putShort(offset, toFixed16(xs[i]))
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buffer.putShort(offset + 2, toFixed16(ys[i]))
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buffer.putShort(offset + 4, toFixed16(zs[i]))
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buffer.put(offset + 6, toConfidenceByte(confidence[i]))
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}
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return buffer.array()
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}
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/** 解码 239 字节帧；非法输入抛 IllegalArgumentException */
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fun decode(bytes: ByteArray): PoseFrame {
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validate(bytes)?.let { throw IllegalArgumentException(it) }
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val buffer = ByteBuffer.wrap(bytes).order(ByteOrder.LITTLE_ENDIAN)
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val frameId = buffer.getInt(4)
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val flags = buffer.get(3).toInt() and 0xFF
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val xs = FloatArray(KEYPOINT_COUNT)
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val ys = FloatArray(KEYPOINT_COUNT)
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val zs = FloatArray(KEYPOINT_COUNT)
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val confidence = FloatArray(KEYPOINT_COUNT)
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for (i in 0 until KEYPOINT_COUNT) {
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val offset = HEADER_SIZE + i * POINT_BYTES
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xs[i] = buffer.getShort(offset) / SCALE.toFloat()
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ys[i] = buffer.getShort(offset + 2) / SCALE.toFloat()
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zs[i] = buffer.getShort(offset + 4) / SCALE.toFloat()
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confidence[i] = (buffer.get(offset + 6).toInt() and 0xFF) / 255f
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}
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return PoseFrame(frameId, flags, xs, ys, zs, confidence)
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}
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/** 依据置信度数组计算是否应置 FLAG_LOW_CONFIDENCE */
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fun computeLowConfidence(confidence: FloatArray): Boolean =
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confidence.any { it < CONFIDENCE_THRESHOLD }
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fun withLowConfidenceFlag(flags: Int, confidence: FloatArray): Int =
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if (computeLowConfidence(confidence)) flags or FLAG_LOW_CONFIDENCE else flags and FLAG_LOW_CONFIDENCE.inv()
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private fun toFixed16(value: Float): Short {
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val scaled = Math.round(value * SCALE)
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return scaled.coerceIn(-32768L, 32767L).toShort()
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}
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private fun toConfidenceByte(value: Float): Byte =
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Math.round(value.coerceIn(0f, 1f) * 255f).coerceIn(0, 255).toByte()
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}
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