| // Copyright 2026 The Wuffs Authors. |
| // |
| // Licensed under the Apache License, Version 2.0 <LICENSE-APACHE or |
| // https://www.apache.org/licenses/LICENSE-2.0> or the MIT license |
| // <LICENSE-MIT or https://opensource.org/licenses/MIT>, at your |
| // option. This file may not be copied, modified, or distributed |
| // except according to those terms. |
| // |
| // SPDX-License-Identifier: Apache-2.0 OR MIT |
| |
| // -------- |
| |
| // Quirks are discussed in (/doc/note/quirks.md). |
| // |
| // The base38 encoding of "vp8." is 0x1B_5EFE. Left shifting by 10 gives |
| // 0x6D7B_F800. |
| pri const QUIRKS_BASE : base.u32 = 0x6D7B_F800 |
| |
| // -------- |
| |
| // Gives the image width and height out-of-band, in the u64 quirk value. The |
| // low 32 bits are the width and the high 32 bits are the height. Both |
| // dimensions should range within 0x0001 ..= 0x3FFF. |
| // |
| // A simple WebP file could contain one chunk, a VP8 chunk, that gives the |
| // image width and height. A complex WebP file could contain three chunks: |
| // VP8X, ALPH and VP8. The image dimensions are given in the VP8X chunk and are |
| // then repeated in the VP8 chunk. |
| // |
| // After a webp.decoder decode_image_config call, the caller might next want to |
| // query the workbuf length, to know how much memory to dynamically allocate, |
| // especially before attempting to decode the ALPH chunk. The outer |
| // webp.decoder workbuf_len method can delegate to the inner vp8.decoder |
| // workbuf_len method, but the latter needs to know the image dimensions. |
| // |
| // This quirk mechanism lets the outer webp decoder tell the inner vp8 decoder |
| // those dimensions, after parsing the VP8X chunk but before ALPH or VP8. |
| pub const QUIRK_WIDTH_AND_HEIGHT : base.u32 = 0x6D7B_F800 | 0x00 |
