[FFmpeg-devel] [PATCH] PCX encoder

[Michael Niedermayer]

On Thu, Mar 19, 2009 at 12:33:41PM -0400, Daniel Verkamp wrote:
> On Wed, Mar 18, 2009 at 9:23 AM, Michael Niedermayer <michaelni at gmx.at> wrote:
> > On Tue, Mar 17, 2009 at 01:14:50PM -0400, Daniel Verkamp wrote:
> > [...]
> >> +static int pcx_rle_encode( ? ? ?uint8_t *dst, int dst_size,
> >> + ? ? ? ? ? ? ? ? ? ? ? ? ?const uint8_t *src, int src_size)
> >> +{
> >> + ? ?int i;
> >> + ? ?uint8_t prev = src[0];
> >> + ? ?int count = 1;
> >> + ? ?const uint8_t *dst_start = dst;
> >> +
> >> + ? ?// check worst-case upper bound on dst_size
> >> + ? ?if (dst_size < 2LL * src_size)
> >> + ? ? ? ?return -1;
> >> +
> >> + ? ?for (i = 1; ; i++) {
> >> + ? ? ? ?if (i != src_size && src[i] == prev && count < 0x3F) {
> >> + ? ? ? ? ? ?// current byte is same as prev
> >> + ? ? ? ? ? ?++count;
> >> + ? ? ? ?} else {
> >> + ? ? ? ? ? ?// output prev * count
> >> + ? ? ? ? ? ?if (count != 1 || prev >= 0xC0)
> >> + ? ? ? ? ? ? ? ?*dst++ = 0xC0 | count;
> >> + ? ? ? ? ? ?*dst++ = prev;
> >> +
> >> + ? ? ? ? ? ?if (i == src_size)
> >> + ? ? ? ? ? ? ? ?return dst - dst_start;
> >> +
> >> + ? ? ? ? ? ?// start new run
> >> + ? ? ? ? ? ?count = 1;
> >> + ? ? ? ? ? ?prev = src[i];
> >> + ? ? ? ?}
> >> + ? ?}
> >> +
> >> + ? ?return 0; // gcc warns even though this cannot be reached
> >
> > does gcc still warn with the current for() ?
> >
> 
> Eliminated in latest patch.
> 
> >
> >> +}
> >> +
> >> +static int pcx_encode_frame(AVCodecContext *avctx,
> >> + ? ? ? ? ? ? ? ? ? ? ? ? ? ?unsigned char *buf, int buf_size, void *data)
> >> +{
> >> + ? ?PCXContext *s = avctx->priv_data;
> >> + ? ?AVFrame *const pict = &s->picture;
> >> + ? ?const uint8_t *buf_start = buf;
> >> + ? ?const uint8_t *buf_end ? = buf + buf_size;
> >> +
> >> + ? ?int bpp, nplanes, i, j, y, p, line_bytes, written, src_line_size;
> >> + ? ?const uint32_t *pal = NULL;
> >> + ? ?const uint8_t *src;
> >> + ? ?uint8_t *plane;
> >> +
> >> + ? ?*pict = *(AVFrame *)data;
> >> + ? ?pict->pict_type = FF_I_TYPE;
> >> + ? ?pict->key_frame = 1;
> >> +
> >> + ? ?if (avctx->width > 65535 || avctx->height > 65535) {
> >> + ? ? ? ?av_log(avctx, AV_LOG_ERROR, "image dimensions do not fit in 16 bits\n");
> >> + ? ? ? ?return -1;
> >> + ? ?}
> >> +
> >> + ? ?switch (avctx->pix_fmt) {
> >> + ? ?case PIX_FMT_RGB24:
> >> + ? ? ? ?bpp = 8;
> >> + ? ? ? ?nplanes = 3;
> >> + ? ? ? ?break;
> >> + ? ?case PIX_FMT_RGB8:
> >> + ? ?case PIX_FMT_BGR8:
> >> + ? ?case PIX_FMT_RGB4_BYTE:
> >> + ? ?case PIX_FMT_BGR4_BYTE:
> >> + ? ?case PIX_FMT_GRAY8:
> >> + ? ?case PIX_FMT_PAL8:
> >> + ? ? ? ?bpp = 8;
> >> + ? ? ? ?nplanes = 1;
> >> + ? ? ? ?pal = (uint32_t *)pict->data[1];
> >> + ? ? ? ?break;
> >> + ? ?case PIX_FMT_MONOBLACK:
> >> + ? ? ? ?bpp = 1;
> >> + ? ? ? ?nplanes = 1;
> >> + ? ? ? ?pal = monoblack_pal;
> >> + ? ? ? ?break;
> >> + ? ?default:
> >> + ? ? ? ?av_log(avctx, AV_LOG_ERROR, "unsupported pixfmt\n");
> >> + ? ? ? ?return -1;
> >> + ? ?}
> >> +
> >> + ? ?line_bytes = (avctx->width * bpp + 7) >> 3;
> >> + ? ?line_bytes = (line_bytes + 1) & ~1;
> >> +
> >> + ? ?bytestream_put_byte(&buf, 10); ? ? ? ? ? ? ? ? ?// manufacturer
> >> + ? ?bytestream_put_byte(&buf, 5); ? ? ? ? ? ? ? ? ? // version
> >> + ? ?bytestream_put_byte(&buf, 1); ? ? ? ? ? ? ? ? ? // encoding
> >> + ? ?bytestream_put_byte(&buf, bpp); ? ? ? ? ? ? ? ? // bits per pixel per plane
> >> + ? ?bytestream_put_le16(&buf, 0); ? ? ? ? ? ? ? ? ? // x min
> >> + ? ?bytestream_put_le16(&buf, 0); ? ? ? ? ? ? ? ? ? // y min
> >> + ? ?bytestream_put_le16(&buf, avctx->width - 1); ? ?// x max
> >> + ? ?bytestream_put_le16(&buf, avctx->height - 1); ? // y max
> >> + ? ?bytestream_put_le16(&buf, 0); ? ? ? ? ? ? ? ? ? // horizontal DPI
> >> + ? ?bytestream_put_le16(&buf, 0); ? ? ? ? ? ? ? ? ? // vertical DPI
> >> + ? ?for (i = 0; i < 16; i++)
> >> + ? ? ? ?bytestream_put_be24(&buf, pal ? pal[i] : 0);// palette (<= 16 color only)
> >> + ? ?bytestream_put_byte(&buf, 0); ? ? ? ? ? ? ? ? ? // reserved
> >> + ? ?bytestream_put_byte(&buf, nplanes); ? ? ? ? ? ? // number of planes
> >> + ? ?bytestream_put_le16(&buf, line_bytes); ? ? ? ? ?// scanline plane size in bytes
> >> +
> >> + ? ?while (buf - buf_start < 128)
> >> + ? ? ? ?*buf++= 0;
> >> +
> >> + ? ?plane = av_mallocz(line_bytes);
> >> + ? ?src = pict->data[0];
> >> + ? ?src_line_size = (avctx->width * nplanes * bpp + 7) >> 3;
> >> +
> >> + ? ?for (y = 0; y < avctx->height; y++) {
> >> + ? ? ? ?for (p = 0; p < nplanes; p++) {
> >> + ? ? ? ? ? ?for (i = p, j = 0; i < src_line_size; i += nplanes, j++) {
> >> + ? ? ? ? ? ? ? ?plane[j] = src[i];
> >> + ? ? ? ? ? ?}
> >> + ? ? ? ? ? ?if ((written = pcx_rle_encode(buf, buf_end - buf,
> >> + ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ?plane, line_bytes)) < 0) {
> >> + ? ? ? ? ? ? ? ?av_log(avctx, AV_LOG_ERROR, "buffer too small\n");
> >> + ? ? ? ? ? ? ? ?av_free(plane);
> >> + ? ? ? ? ? ? ? ?return -1;
> >> + ? ? ? ? ? ?}
> >
> > i think plane could be avoided by passing nplanes into pcx_rle_encode()
> > and i think that wouldnt make pcx_rle_encode uglier ...
> >
> 
> Ok, reworked to move the plane handling into pcx_rle_encode().

[...]
> +static int pcx_rle_encode(      uint8_t *dst, int dst_size,
> +                          const uint8_t *src, int src_plane_size, int nplanes)
> +{
> +    int p;
> +    const uint8_t *dst_start = dst;
> +
> +    // check worst-case upper bound on dst_size
> +    if (dst_size < 2LL * src_plane_size * nplanes || src_plane_size <= 0)
> +        return -1;
> +
> +    for (p = 0; p < nplanes; p++) {

i would have expected that to be outside the function but thats not
a request to change it, just a note


> +        int i, count = 1;
> +        const uint8_t *src_plane = src + p;
> +        uint8_t prev = *src_plane;
> +        src_plane += nplanes;
> +
> +        for (i = 1; ; i++, src_plane += nplanes) {
> +            if (i != src_plane_size && *src_plane == prev && count < 0x3F) {
> +                // current byte is same as prev
> +                ++count;
> +            } else {
> +                // output prev * count
> +                if (count != 1 || prev >= 0xC0)
> +                    *dst++ = 0xC0 | count;
> +                *dst++ = prev;
> +
> +                if (i == src_plane_size)
> +                    break;
> +
> +                // start new run
> +                count = 1;
> +                prev = *src_plane;
> +            }
> +        }

the number of variables in this loop can be reduced
a changed src_plane_size can be checked against src_plane thus making
i unneeded

[...]
-- 
Michael     GnuPG fingerprint: 9FF2128B147EF6730BADF133611EC787040B0FAB

Awnsering whenever a program halts or runs forever is
On a turing machine, in general impossible (turings halting problem).
On any real computer, always possible as a real computer has a finite number
of states N, and will either halt in less than N cycles or never halt.
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