libswscale/graph.h

/*
 * Copyright (C) 2024 Niklas Haas
 *
 * This file is part of FFmpeg.
 *
 * FFmpeg is free software; you can redistribute it and/or
 * modify it under the terms of the GNU Lesser General Public
 * License as published by the Free Software Foundation; either
 * version 2.1 of the License, or (at your option) any later version.
 *
 * FFmpeg is distributed in the hope that it will be useful,
 * but WITHOUT ANY WARRANTY; without even the implied warranty of
 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
 * Lesser General Public License for more details.
 *
 * You should have received a copy of the GNU Lesser General Public
 * License along with FFmpeg; if not, write to the Free Software
 * Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA
 */

#ifndef SWSCALE_GRAPH_H
#define SWSCALE_GRAPH_H

#include <stdbool.h>

#include "libavutil/slicethread.h"
#include "libavutil/buffer.h"

#include "swscale.h"
#include "format.h"
#include "lut3d.h"

static av_always_inline av_const int ff_fmt_vshift(enum AVPixelFormat fmt, int plane)
{
    const AVPixFmtDescriptor *desc = av_pix_fmt_desc_get(fmt);
    return (plane == 1 || plane == 2) ? desc->log2_chroma_h : 0;
}

typedef struct SwsPass  SwsPass;
typedef struct SwsGraph SwsGraph;

/**
 * Output `h` lines of filtered data. `out` and `in` point to the
 * start of the image buffer for this pass.
 */
typedef void (*SwsPassFunc)(const SwsFrame *out, const SwsFrame *in,
                            int y, int h, const SwsPass *pass);

/**
 * Function to run from the main thread before processing any lines.
 */
typedef int (*SwsPassSetup)(const SwsFrame *out, const SwsFrame *in,
                            const SwsPass *pass);

/**
 * Represents an output buffer for a filter pass. During filter graph
 * construction, these merely hold the metadata. Allocation of the underlying
 * storage is deferred until after all filter passes are settled.
 */
typedef struct SwsPassBuffer {
    SwsFrame frame;

    int width, height; /* dimensions of this buffer */
    AVFrame *avframe;  /* backing storage for `frame` */

    /* Optional allocation hints for optimal performance */
    int width_align;   /* Align width to multiple of this */
    int width_pad;     /* Extra padding pixels */

    /**
     * Map of planes which are directly copied from the pass input. These
     * may be promoted from a memcpy to a refcopy.
     *
     * Each entry maps the output index to the corresponding input plane
     * index, or -1 for no copythrough.
     */
    int plane_copy[4];
} SwsPassBuffer;

/**
 * Represents a single filter pass in the scaling graph. Each filter will
 * read from some previous pass's output, and write to a buffer associated
 * with the pass (or into the final output image).
 */
struct SwsPass {
    const SwsGraph *graph;

    /**
     * Filter main execution function. Called from multiple threads, with
     * the granularity dictated by `slice_h`. Individual slices sent to `run`
     * are always equal to (or smaller than, for the last slice) `slice_h`.
     */
    SwsPassFunc run;
    SwsBackend backend; /* backend this pass is using, or 0 */
    enum AVPixelFormat format; /* new pixel format */
    int lines;         /* pass dispatch size */
    int slice_h;       /* filter granularity */
    int num_slices;

    /**
     * Filter input. This pass's output will be resolved to form this pass's.
     * input. If NULL, the original input image is used.
     */
    SwsPass *input;

    /**
     * Filter output buffer. This struct is always allocated.
     */
    SwsPassBuffer *output; /* refstruct */

    /**
     * Called once from the main thread before running the filter. Optional.
     * Returns 0 or a negative error code.
     */
    SwsPassSetup setup;

    /**
     * Optional private state and associated free() function.
     */
    void (*free)(void *priv);
    void *priv;
};

/**
 * Align `width` to the optimal size for `pass`.
 */
int ff_sws_pass_aligned_width(const SwsPass *pass, int width);

/**
 * Filter graph, which represents a 'baked' pixel format conversion.
 */
typedef struct SwsGraph {
    SwsContext *ctx;
    AVSliceThread *slicethread;
    int num_threads; /* resolved at init() time */
    bool incomplete; /* set during init() if formats had to be inferred */
    bool noop;       /* set during init() if the graph is a no-op */
    SwsBackend backend; /* backends this graph is using, set during init() */

    AVBufferRef *hw_frames_ref;

    /**
     * Map of planes which directly copied from the input. These may be
     * promoted from a memcpy to a refcopy. This requires special handling
     * by the caller.
     *
     * Each entry maps the output index to the corresponding input plane
     * index, or -1 for no copythrough.
     */
    int plane_copy[4];

    /** Sorted sequence of filter passes to apply */
    SwsPass **passes;
    int num_passes;

    /**
     * Cached copy of the public options that were used to construct this
     * SwsGraph. Used only to detect when the graph needs to be reinitialized.
     */
    SwsContext opts_copy;

    /**
     * Currently active format and processing parameters.
     */
    SwsFormat src, dst;

    /**
     * 3DLUT state used for gamut/tone mapping. (Optional)
     */
    SwsLut3D *lut3d; /* refstruct */

    /**
     * Temporary execution state inside ff_sws_graph_run(); used to pass
     * data to worker threads.
     */
    struct {
        const SwsPass *pass; /* current filter pass */
        const SwsFrame *input; /* current filter pass input/output */
        const SwsFrame *output;
    } exec;
} SwsGraph;

/**
 * Allocate an empty SwsGraph. Returns NULL on failure.
 */
SwsGraph *ff_sws_graph_alloc(void);

/**
 * Initialize the filter graph for a given pair of formats. Returns 0 or a
 * negative error.
 */
int ff_sws_graph_init(SwsGraph *graph, SwsContext *ctx, const SwsFormat *dst,
                      const SwsFormat *src);


/**
 * Allocate and add a new pass to the filter graph. Takes over ownership of
 * `priv`, even on failure.
 *
 * @param graph  Filter graph to add the pass to.
 * @param fmt    Pixel format of the output image.
 * @param w      Width of the output image.
 * @param h      Height of the output image.
 * @param input  Previous pass to read from, or NULL for the input image.
 * @param lines  Override the number of lines processed for this pass. (Optional)
 * @param align  Minimum slice alignment for this pass, or 0 for no threading.
 * @param run    Filter function to run.
 * @param setup  Optional setup function to run from the main thread.
 * @param priv   Private state for the filter run function.
 * @param free   Function to free the private state.
 * @param out_pass The newly added pass will be written here on success.
 * @return 0 or a negative error code
 */
int ff_sws_graph_add_pass(SwsGraph *graph, enum AVPixelFormat fmt,
                          int width, int height, SwsPass *input,
                          int lines, int align,
                          SwsPassFunc run, SwsPassSetup setup,
                          void *priv, void (*free)(void *priv),
                          SwsPass **out_pass);

/**
 * Link the output buffers to a different pass, rather than allocating
 * new image buffers. This allows reusing the same buffer for multiple passes,
 * e.g. in the case of in-place passes or partial passes that modify different
 * planes.
 *
 * Any existing buffer on `dst` will be ignored/unref'd.
 **/
void ff_sws_pass_link_output(SwsPass *dst, const SwsPass *src);

/**
 * Remove all passes added since the given index.
 */
void ff_sws_graph_rollback(SwsGraph *graph, int since_idx);

/**
 * Uninitialize any state associate with this filter graph and free it.
 */
void ff_sws_graph_free(SwsGraph **graph);

/**
 * Update dynamic per-frame HDR metadata without requiring a full reinit.
 */
void ff_sws_graph_update_metadata(SwsGraph *graph, const SwsColor *color);

/**
 * Wrapper around ff_sws_graph_init() that reuses the existing graph if the
 * format is compatible. This will also update dynamic per-frame metadata.
 *
 * Must also be called after changing any of the fields in `ctx`, or else they
 * will have no effect.
 */
int ff_sws_graph_reinit(SwsGraph *graph, SwsContext *ctx, const SwsFormat *dst,
                        const SwsFormat *src);

/**
 * Dispatch the filter graph on a single field of the given frames. Internally
 * threaded.
 */
int ff_sws_graph_run(SwsGraph *graph, const AVFrame *dst, const AVFrame *src);

#endif /* SWSCALE_GRAPH_H */