daedalus-decoder/include/daedalus_decoder.h

/* SPDX-License-Identifier: BSD-2-Clause */
/*
 * daedalus-decoder — public C API.
 *
 * Frame-level GPU H.264 decoder targeting V3D7 (Raspberry Pi 5).  Built
 * on daedalus-fourier's V3D compute primitives at frame granularity —
 * one Vulkan submit per frame, one fence wait per frame, encoded
 * bitstream in (via libavcodec's per-MB intercept), NV12 frame out.
 *
 * Per the 2026-05-24 Phase 1 design decisions:
 *   - libavcodec intercept is at macroblock-level (substitution-arc
 *     evolution): the caller is expected to drive the per-MB CABAC /
 *     CAVLC entropy decode and feed each macroblock's descriptor +
 *     coefficients via daedalus_decoder_append_mb().  flush_frame()
 *     builds the per-frame VkCommandBuffer and submits.
 *   - DPB is Vulkan-native VkImage with VK_KHR_external_memory_dma_buf
 *     export.  The caller can obtain the output frame's dmabuf fd
 *     via daedalus_decoder_export_dmabuf().
 *   - Daemon integration shape: this library is statically linked into
 *     daedalus_v4l2_daemon.  No IPC.
 *
 * STATUS: scaffold.  No GPU pipeline implemented yet; all functions
 * are stubs that compile but do not decode anything.  See DESIGN.md
 * for the architecture.
 *
 * ABI: pre-0.1 — every signature here may change.  Don't rely on
 * stability yet.
 */
#ifndef DAEDALUS_DECODER_H
#define DAEDALUS_DECODER_H

#include <stddef.h>
#include <stdint.h>

#ifdef __cplusplus
extern "C" {
#endif

/* -------------------------------------------------------------------
 * Opaque decoder context.  One per concurrent stream.
 * ----------------------------------------------------------------- */
typedef struct daedalus_decoder daedalus_decoder;

/* -------------------------------------------------------------------
 * Per-macroblock input.  Mirrors §3 of DESIGN.md.  The caller's
 * libavcodec intercept populates this from the H264SliceContext
 * fields after ff_h264_decode_mb_cabac/cavlc returns and before
 * ff_h264_hl_decode_mb is supposed to run (we replace the latter).
 * ----------------------------------------------------------------- */
struct daedalus_decoder_mb_input {
    /* Frame coordinates (macroblock units). */
    uint16_t mb_x;
    uint16_t mb_y;

    /* Type + quantisation. */
    uint8_t  mb_type;            /* H.264 spec table 7-13/7-14/7-17/7-18 enum */
    uint8_t  mb_qp_y;
    uint8_t  mb_qp_uv;
    uint8_t  cbp;                /* coded block pattern, 0..47 */

    /* Intra prediction (used iff mb_type == I_NxN or I_16x16). */
    uint8_t  intra_4x4_modes[16];
    uint8_t  intra_16x16_mode;
    uint8_t  intra_chroma_mode;

    /* Inter motion / partitions (used iff P_* or B_*). */
    uint8_t  partition_mode;     /* P_16x16 / P_16x8 / P_8x16 / P_8x8 / etc. */
    int8_t   ref_idx_l0[4];      /* per partition; -1 = not used */
    int8_t   ref_idx_l1[4];      /* B only */
    int16_t  mv_l0[4][2];        /* qpel precision (1/4 sample); (x, y) */
    int16_t  mv_l1[4][2];

    /* Deblocking filter parameters. */
    uint8_t  deblock_disable;    /* 0 = enabled */
    int8_t   deblock_alpha_c0;
    int8_t   deblock_beta;

    /* Transform coefficients — 256 luma (4x4 x 16) + 64 cb + 64 cr,
     * column-major within each 4x4 block (matches FFmpeg convention).
     * Caller-owned; copied during append. */
    const int16_t *coeffs;       /* points at exactly 384 int16_t */
};

/* -------------------------------------------------------------------
 * Output frame format selector.
 * ----------------------------------------------------------------- */
typedef enum {
    DAEDALUS_DECODER_OUTPUT_NV12 = 0,   /* default; Stage 4 final */
    DAEDALUS_DECODER_OUTPUT_RGBA = 1,   /* Stage 5 opt-in */
} daedalus_decoder_output_format;

/* -------------------------------------------------------------------
 * Lifecycle
 * ----------------------------------------------------------------- */

/* Create a decoder context for the given **coded** frame dimensions.
 *
 * width, height: pixels of the H.264 coded picture, NOT the displayed
 * picture.  Both must be multiples of 16 (macroblock granularity).
 * For displayed 1080p (1920×1080), the coded frame is 1920×1088 with
 * the SPS's `frame_cropping_*` offsets cropping the bottom 8 rows.
 * The caller is responsible for translating from SPS dims + crop
 * rectangle to the values passed here; we decode the coded frame.
 *
 * Returns NULL on bad dimensions or allocation failure.  Returns a
 * usable context with daedalus_decoder_has_qpu() == 0 when Vulkan
 * init fails — callers that need GPU work should check has_qpu
 * before relying on it.
 */
daedalus_decoder *daedalus_decoder_create(int width, int height);

/* Free all resources.  Safe with NULL. */
void daedalus_decoder_destroy(daedalus_decoder *dec);

/* Switch output format BEFORE the first append_mb call of a frame.
 * Default is NV12.  Returns 0 on success, -1 if called mid-frame
 * (caller must flush first). */
int daedalus_decoder_set_output_format(daedalus_decoder *dec,
                                        daedalus_decoder_output_format fmt);

/* -------------------------------------------------------------------
 * Per-frame submission
 * ----------------------------------------------------------------- */

/* Append one macroblock's data to the current frame's descriptor SSBO
 * + coefficient SSBO.  No GPU dispatch yet — just CPU-side writes.
 *
 * Must be called in raster order (mb_y * mb_width + mb_x) for the
 * intra-prediction wavefront to work correctly in Phase 1.
 *
 * Returns 0 on success, negative on bounds violation or OOM.
 */
int daedalus_decoder_append_mb(daedalus_decoder *dec,
                                const struct daedalus_decoder_mb_input *mb);

/* End-of-frame flush: builds the per-frame VkCommandBuffer with all
 * pipeline stages, submits once, waits on a single fence, copies the
 * NV12 (or RGBA when opted in) output into the caller-provided
 * planes.
 *
 * For NV12:
 *   out_y / y_stride: Y plane (W*H bytes minimum, at the given stride)
 *   out_uv / uv_stride: interleaved UV plane (W*(H/2) bytes minimum)
 *
 * For RGBA: out_y receives 4*W*H bytes at y_stride; out_uv ignored.
 *
 * Returns 0 on success, negative on Vulkan failure or undecodable
 * frame.  After return, the decoder is ready for the next frame's
 * append calls.
 */
int daedalus_decoder_flush_frame(daedalus_decoder *dec,
                                  uint8_t *out_y,  size_t y_stride,
                                  uint8_t *out_uv, size_t uv_stride);

/* Export the most-recently-decoded frame as a dma_buf fd.  The fd is
 * owned by the caller and must be closed when done.  Lets V4L2
 * consumers (daedalus_v4l2_daemon, libva-v4l2-request-fourier) attach
 * the GPU-decoded surface directly to a CAPTURE plane without a CPU
 * round-trip.
 *
 * Returns the dmabuf fd on success, -1 on failure.  Must be called
 * AFTER flush_frame returns for the relevant frame.
 */
int daedalus_decoder_export_dmabuf(daedalus_decoder *dec, int plane);

/* -------------------------------------------------------------------
 * Diagnostics
 * ----------------------------------------------------------------- */

/* daedalus-decoder build version (semver string, e.g. "0.0.1+g0a1b2c3"). */
const char *daedalus_decoder_version(void);

/* Whether the underlying daedalus-fourier context picked up a working
 * V3D7 Vulkan instance.  Returns 0 if Vulkan init failed and the
 * decoder is operating in stub / failure mode. */
int daedalus_decoder_has_qpu(const daedalus_decoder *dec);

#ifdef __cplusplus
}
#endif

#endif /* DAEDALUS_DECODER_H */