| // Copyright 2017 The Wuffs Authors. |
| // |
| // Licensed under the Apache License, Version 2.0 (the "License"); |
| // you may not use this file except in compliance with the License. |
| // You may obtain a copy of the License at |
| // |
| // https://www.apache.org/licenses/LICENSE-2.0 |
| // |
| // Unless required by applicable law or agreed to in writing, software |
| // distributed under the License is distributed on an "AS IS" BASIS, |
| // WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. |
| // See the License for the specific language governing permissions and |
| // limitations under the License. |
| |
| // -------- |
| |
| // Quirks are discussed in (/doc/note/quirks.md). |
| // |
| // The base38 encoding of "gif " is 0x0F_8586. Left shifting by 10 gives |
| // 0x3E16_1800. |
| pri const QUIRKS_BASE : base.u32 = 0x3E16_1800 |
| |
| // -------- |
| |
| // When this quirk is enabled, when skipping over frames, the number of frames |
| // visited isn't incremented when the last byte of the N'th frame is seen. |
| // Instead, it is incremented when the first byte of the N+1'th frame's header |
| // is seen. There may be zero or more GIF extensions between the N'th frame's |
| // payload and the N+1'th frame's header. |
| // |
| // For a well-formed GIF, this won't have much effect. For a malformed GIF, |
| // this can affect the number of valid frames, if there is an error detected in |
| // the extensions between one frame's payload and the next frame's header. |
| // |
| // Some other GIF decoders don't register the N'th frame as complete until they |
| // see the N+1'th frame's header (or the end-of-animation terminator), so that |
| // e.g. the API for visiting the N'th frame can also return whether it's the |
| // final frame. Enabling this quirk allows for matching that behavior. |
| pub const QUIRK_DELAY_NUM_DECODED_FRAMES : base.u32 = 0x3E16_1800 | 0x00 |
| |
| // When this quirk is enabled, the background color of the first frame is set |
| // to black whenever that first frame has a local (frame-specific) palette. |
| // That black can be either opaque black or transparent black, depending on |
| // whether or not that first frame is opaque: whether that local palette |
| // contains a transparent color. |
| // |
| // This has no effect unless QUIRK_HONOR_BACKGROUND_COLOR is also enabled. |
| // |
| // There isn't really much of a rationale for this, other than it matches the |
| // behavior of another GIF implementation. |
| pub const QUIRK_FIRST_FRAME_LOCAL_PALETTE_MEANS_BLACK_BACKGROUND : base.u32 = 0x3E16_1800 | 0x01 |
| |
| // When this quirk is enabled, the background color is taken from the GIF |
| // instead of always being transparent black. If the background color index in |
| // the GIF header is non-zero but less than the global palette's size, the |
| // global background color is that global palette's entry. Otherwise, it is |
| // opaque black. A frame's background color is transparent if the frame palette |
| // contains a transparent color. Otherwise, it is the global background color. |
| // Note that different frames can have different background colors. |
| // |
| // Specifically, if the initial frame bounds is smaller than the image bounds, |
| // those pixels outside the initial frame bounds are assumed to start as that |
| // frame background color. The frame background color should also be used when |
| // processing WUFFS_BASE__ANIMATION_DISPOSAL__RESTORE_BACKGROUND. In both |
| // cases, the caller of Wuffs, not Wuffs itself, is responsible for filling the |
| // pixel buffer with that color. |
| pub const QUIRK_HONOR_BACKGROUND_COLOR : base.u32 = 0x3E16_1800 | 0x02 |
| |
| // When this quirk is enabled, silently ignore e.g. a frame that reports a |
| // width and height of 6 pixels each, followed by 50 pixel values. In that |
| // case, we process the first 36 pixel values and discard the excess 14. |
| pub const QUIRK_IGNORE_TOO_MUCH_PIXEL_DATA : base.u32 = 0x3E16_1800 | 0x03 |
| |
| // When this quirk is enabled, if the initial frame bounds extends beyond the |
| // image bounds, then the image bounds stay unchanged. By default (with this |
| // quirk disabled), the image bounds are adjusted to always contain the first |
| // frame's bounds (but not necessarily subsequent frame's bounds). |
| // |
| // For more discussion, see |
| // https://github.com/google/wuffs/blob/main/test/data/artificial/gif-frame-out-of-bounds.gif.make-artificial.txt |
| pub const QUIRK_IMAGE_BOUNDS_ARE_STRICT : base.u32 = 0x3E16_1800 | 0x04 |
| |
| // When this quirk is enabled, a frame with zero width or height is rejected |
| // during decode_frame (but accepted during decode_frame_config). |
| pub const QUIRK_REJECT_EMPTY_FRAME : base.u32 = 0x3E16_1800 | 0x05 |
| |
| // When this quirk is enabled, a frame with no explicit palette is rejected, |
| // instead of implicitly having a palette with every entry being opaque black. |
| pub const QUIRK_REJECT_EMPTY_PALETTE : base.u32 = 0x3E16_1800 | 0x06 |
| |
| pri const QUIRKS_COUNT : base.u32 = 0x07 |
