libvpx中的decode_partition
Howard Yin 2022-10-21 07:00:04 视频编解码源码解读libvpx
终于要接近最深处了，这是decode_partition：
static void decode_partition(TileWorkerData *twd, VP9Decoder *const pbi,
int mi_row, int mi_col, BLOCK_SIZE bsize,
int n4x4_l2) {
VP9_COMMON *const cm = &pbi->common;
const int n8x8_l2 = n4x4_l2 - 1;
const int num_8x8_wh = 1 << n8x8_l2;
const int hbs = num_8x8_wh >> 1;
PARTITION_TYPE partition;
BLOCK_SIZE subsize;
const int has_rows = (mi_row + hbs) < cm->mi_rows;
const int has_cols = (mi_col + hbs) < cm->mi_cols;
MACROBLOCKD *const xd = &twd->xd;
if (mi_row >= cm->mi_rows || mi_col >= cm->mi_cols) return;
partition = read_partition(twd, mi_row, mi_col, has_rows, has_cols, n8x8_l2);
subsize = subsize_lookup[partition][bsize]; // get_subsize(bsize, partition);
if (!hbs) {
// calculate bmode block dimensions (log 2)
xd->bmode_blocks_wl = 1 >> !!(partition & PARTITION_VERT);
xd->bmode_blocks_hl = 1 >> !!(partition & PARTITION_HORZ);
decode_block(twd, pbi, mi_row, mi_col, subsize, 1, 1);
} else {
switch (partition) {
case PARTITION_NONE:
decode_block(twd, pbi, mi_row, mi_col, subsize, n4x4_l2, n4x4_l2);
break;
case PARTITION_HORZ:
decode_block(twd, pbi, mi_row, mi_col, subsize, n4x4_l2, n8x8_l2);
if (has_rows)
decode_block(twd, pbi, mi_row + hbs, mi_col, subsize, n4x4_l2,
n8x8_l2);
break;
case PARTITION_VERT:
decode_block(twd, pbi, mi_row, mi_col, subsize, n8x8_l2, n4x4_l2);
if (has_cols)
decode_block(twd, pbi, mi_row, mi_col + hbs, subsize, n8x8_l2,
n4x4_l2);
break;
case PARTITION_SPLIT:
decode_partition(twd, pbi, mi_row, mi_col, subsize, n8x8_l2);
decode_partition(twd, pbi, mi_row, mi_col + hbs, subsize, n8x8_l2);
decode_partition(twd, pbi, mi_row + hbs, mi_col, subsize, n8x8_l2);
decode_partition(twd, pbi, mi_row + hbs, mi_col + hbs, subsize,
n8x8_l2);
break;
default: assert(0 && "Invalid partition type");
}
}
// update partition context
if (bsize >= BLOCK_8X8 &&
(bsize == BLOCK_8X8 || partition != PARTITION_SPLIT))
dec_update_partition_context(twd, mi_row, mi_col, subsize, num_8x8_wh);
}
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可以看见，很短， 核心部分就是一个switch下套4个条件，里面有递归的decode_partition和一个decode_block函数。
这个递归的条件PARTITION_SPLIT很明显就是把区域再分四块进行解码，对应编码器里可变大小编码块的知识。
所以再往下一层就是这个decode_block了：
static void decode_block(TileWorkerData *twd, VP9Decoder *const pbi, int mi_row,
int mi_col, BLOCK_SIZE bsize, int bwl, int bhl) {
VP9_COMMON *const cm = &pbi->common;
const int less8x8 = bsize < BLOCK_8X8;
const int bw = 1 << (bwl - 1);
const int bh = 1 << (bhl - 1);
const int x_mis = VPXMIN(bw, cm->mi_cols - mi_col);
const int y_mis = VPXMIN(bh, cm->mi_rows - mi_row);
vpx_reader *r = &twd->bit_reader;
MACROBLOCKD *const xd = &twd->xd;
MODE_INFO *mi = set_offsets(cm, xd, bsize, mi_row, mi_col, bw, bh, x_mis,
y_mis, bwl, bhl);
if (bsize >= BLOCK_8X8 && (cm->subsampling_x || cm->subsampling_y)) {
const BLOCK_SIZE uv_subsize =
ss_size_lookup[bsize][cm->subsampling_x][cm->subsampling_y];
if (uv_subsize == BLOCK_INVALID)
vpx_internal_error(xd->error_info, VPX_CODEC_CORRUPT_FRAME,
"Invalid block size.");
}
vp9_read_mode_info(twd, pbi, mi_row, mi_col, x_mis, y_mis);
if (mi->skip) {
dec_reset_skip_context(xd);
}
if (!is_inter_block(mi)) {
int plane;
for (plane = 0; plane < MAX_MB_PLANE; ++plane) {
const struct macroblockd_plane *const pd = &xd->plane[plane];
const TX_SIZE tx_size = plane ? get_uv_tx_size(mi, pd) : mi->tx_size;
const int num_4x4_w = pd->n4_w;
const int num_4x4_h = pd->n4_h;
const int step = (1 << tx_size);
int row, col;
const int max_blocks_wide =
num_4x4_w + (xd->mb_to_right_edge >= 0
? 0
: xd->mb_to_right_edge >> (5 + pd->subsampling_x));
const int max_blocks_high =
num_4x4_h + (xd->mb_to_bottom_edge >= 0
? 0
: xd->mb_to_bottom_edge >> (5 + pd->subsampling_y));
xd->max_blocks_wide = xd->mb_to_right_edge >= 0 ? 0 : max_blocks_wide;
xd->max_blocks_high = xd->mb_to_bottom_edge >= 0 ? 0 : max_blocks_high;
for (row = 0; row < max_blocks_high; row += step)
for (col = 0; col < max_blocks_wide; col += step)
predict_and_reconstruct_intra_block(twd, mi, plane, row, col,
tx_size);
}
} else {
// Prediction
dec_build_inter_predictors_sb(pbi, xd, mi_row, mi_col);
// Reconstruction
if (!mi->skip) {
int eobtotal = 0;
int plane;
for (plane = 0; plane < MAX_MB_PLANE; ++plane) {
const struct macroblockd_plane *const pd = &xd->plane[plane];
const TX_SIZE tx_size = plane ? get_uv_tx_size(mi, pd) : mi->tx_size;
const int num_4x4_w = pd->n4_w;
const int num_4x4_h = pd->n4_h;
const int step = (1 << tx_size);
int row, col;
const int max_blocks_wide =
num_4x4_w + (xd->mb_to_right_edge >= 0
? 0
: xd->mb_to_right_edge >> (5 + pd->subsampling_x));
const int max_blocks_high =
num_4x4_h +
(xd->mb_to_bottom_edge >= 0
? 0
: xd->mb_to_bottom_edge >> (5 + pd->subsampling_y));
xd->max_blocks_wide = xd->mb_to_right_edge >= 0 ? 0 : max_blocks_wide;
xd->max_blocks_high = xd->mb_to_bottom_edge >= 0 ? 0 : max_blocks_high;
for (row = 0; row < max_blocks_high; row += step)
for (col = 0; col < max_blocks_wide; col += step)
eobtotal +=
reconstruct_inter_block(twd, mi, plane, row, col, tx_size);
}
if (!less8x8 && eobtotal == 0) mi->skip = 1; // skip loopfilter
}
}
xd->corrupted |= vpx_reader_has_error(r);
if (cm->lf.filter_level) {
vp9_build_mask(cm, mi, mi_row, mi_col, bw, bh);
}
}
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