zenwebp 0.4.2

High-performance WebP encoding and decoding in pure Rust
Documentation 
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//! An implementation of the VP8 Video Codec
//!
//! This module contains a partial implementation of the
//! VP8 video format as defined in RFC-6386.
//!
//! It decodes Keyframes only.
//! VP8 is the underpinning of the WebP image format
//!
//! # Related Links
//! * [rfc-6386](http://tools.ietf.org/html/rfc6386) - The VP8 Data Format and Decoding Guide
//! * [VP8.pdf](http://static.googleusercontent.com/media/research.google.com/en//pubs/archive/37073.pdf) - An overview of of the VP8 format

#![allow(clippy::too_many_arguments)]
#![allow(clippy::needless_range_loop)]
#![allow(clippy::collapsible_else_if)]

use alloc::boxed::Box;
use alloc::vec::Vec;
use core::default::Default;

use crate::common::types::*;

// ============================================================================
// Diagnostic Types for I4 Encoding Efficiency Analysis
// ============================================================================

/// Raw quantized coefficient levels for a single 4x4 block (pre-dequantization).
/// Captures the exact values written to the bitstream for comparison with libwebp.
#[doc(hidden)]
#[derive(Clone, Copy, Debug, Default)]
pub struct BlockDiagnostic {
    /// Raw quantized levels in zigzag order (before dequantization)
    pub levels: [i32; 16],
    /// Number of coefficients decoded (0 = all-zero block, position of last nonzero + 1)
    pub eob_position: u8,
}

/// Diagnostic capture for a single macroblock's encoded state.
#[doc(hidden)]
#[derive(Clone, Debug, Default)]
pub struct MacroblockDiagnostic {
    /// Luma prediction mode for this macroblock.
    pub luma_mode: LumaMode,
    /// Chroma prediction mode for this macroblock.
    pub chroma_mode: ChromaMode,
    /// Segment index (0-3).
    pub segment_id: u8,
    /// Whether all coefficients were skipped (zero block).
    pub coeffs_skipped: bool,
    /// I4 sub-block prediction modes (only valid when luma_mode == LumaMode::B)
    pub bpred_modes: [IntraMode; 16],
    /// Y2 (WHT) block coefficients (only used for non-I4 modes)
    pub y2_block: BlockDiagnostic,
    /// 16 Y blocks (4x4 each)
    pub y_blocks: [BlockDiagnostic; 16],
    /// 8 UV blocks (4 U + 4 V)
    pub uv_blocks: [BlockDiagnostic; 8],
}

/// Complete diagnostic capture for a decoded VP8 frame.
/// Allows comparison of intermediate encoding state between zenwebp and libwebp.
#[doc(hidden)]
#[derive(Clone, Debug)]
pub struct DiagnosticFrame {
    /// Width in macroblocks.
    pub mb_width: u16,
    /// Height in macroblocks.
    pub mb_height: u16,
    /// Per-segment quantizer values: (ydc, yac, y2dc, y2ac, uvdc, uvac)
    pub segments: [(i16, i16, i16, i16, i16, i16); 4],
    /// All macroblocks in raster order
    pub macroblocks: Vec<MacroblockDiagnostic>,
    /// Final token probability tables (for comparing probability updates)
    pub token_probs: Box<TokenProbTreeNodes>,
    /// Size of partition 0 (header + mode data)
    pub partition0_size: u32,
}

/// VP8 probability tree node for coefficient decoding.
#[doc(hidden)]
#[derive(Clone, Copy, Debug)]
pub struct TreeNode {
    /// Left branch index or value.
    pub left: u8,
    /// Right branch index or value.
    pub right: u8,
    /// Probability for this branch.
    pub prob: Prob,
    /// Index in the tree.
    pub index: u8,
}

impl TreeNode {
    pub(crate) const fn value_from_branch(t: u8) -> i8 {
        (t & !0x80) as i8
    }
}

type TokenProbTreeNodes = [[[[TreeNode; NUM_DCT_TOKENS - 1]; 3]; 8]; 4];