Struct TxTypeCtx 

pub struct TxTypeCtx<'a> {
    pub set: IntraTxSet,
    pub intra_cdfs: &'a mut IntraTxTypeCdfs,
    pub intra_dir: usize,
    pub uv_mode: usize,
    pub qindex_positive: bool,
    pub lossless: bool,
}

How a coded block’s PlaneTxType is resolved once all_zero shows the block carries coefficients (compute_tx_type / transform_type, §5.11.40–47).

Luma reads the intra_tx_type symbol at this point — its spec position, after all_zero and before eob_pt; chroma derives its type from the prediction mode without consuming a symbol. A zero quantiser (the lossless path) or a DCT_DCT-only set forces DCT_DCT.

Fields

set: IntraTxSet

The intra transform set for this size (get_tx_set).

intra_cdfs: &'a mut IntraTxTypeCdfs

The adapting intra_tx_type CDFs; only luma reads them.

intra_dir: usize

intraDir for the luma symbol’s context.

uv_mode: usize

UVMode for the chroma (plane > 0) derivation.

qindex_positive: bool

Whether the segment’s quantiser index (get_qindex(1, segment_id)) is non-zero; only then is a luma intra_tx_type symbol coded.

lossless: bool

The block’s Lossless: every plane is then DCT_DCT (the WHT path).