std/png/common_consts.wuffs

// Copyright 2020 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.

pub status "#bad animation sequence number"
pub status "#bad checksum"
pub status "#bad chunk"
pub status "#bad filter"
pub status "#bad header"
pub status "#missing palette"
pub status "#unsupported PNG compression method"
pub status "#unsupported PNG file"

pri status "#internal error: inconsistent chunk type"
pri status "#internal error: inconsistent frame bounds"
pri status "#internal error: inconsistent workbuf length"
pri status "#internal error: zlib decoder did not exhaust its input"

pub const DECODER_WORKBUF_LEN_MAX_INCL_WORST_CASE : base.u64 = 0

// DECODER_SRC_IO_BUFFER_LENGTH_MIN_INCL is the minimum length of the src
// wuffs_base__io_buffer passed to the decoder.
pub const DECODER_SRC_IO_BUFFER_LENGTH_MIN_INCL : base.u64 = 8

// ANCILLARY_BIT is the upper/lower case bit on the chunk type's first byte (in
// little-endian order).
pri const ANCILLARY_BIT : base.u32 = 0x0000_0020

// INTERLACING holds the Adam7 interlacing pattern, involving 7 passes:
//  1 6 4 6 2 6 4 6
//  7 7 7 7 7 7 7 7
//  5 6 5 6 5 6 5 6
//  7 7 7 7 7 7 7 7
//  3 6 4 6 3 6 4 6
//  7 7 7 7 7 7 7 7
//  5 6 5 6 5 6 5 6
//  7 7 7 7 7 7 7 7
//
// The six elements of each inner array are:
//  0: log2(x_stride)
//  1: x_stride - x_offset - 1
//  2: x_offset
//  3: log2(y_stride)
//  4: y_stride - y_offset - 1
//  5: y_offset
pri const INTERLACING : array[8] array[6] base.u8[..= 7] = [
	[0, 0, 0, 0, 0, 0],  // non-interlaced; xy_stride=1, xy_offset=0
	[3, 7, 0, 3, 7, 0],  // interlace_pass == 1
	[3, 3, 4, 3, 7, 0],  // interlace_pass == 2
	[2, 3, 0, 3, 3, 4],  // interlace_pass == 3
	[2, 1, 2, 2, 3, 0],  // interlace_pass == 4
	[1, 1, 0, 2, 1, 2],  // interlace_pass == 5
	[1, 0, 1, 1, 1, 0],  // interlace_pass == 6
	[0, 0, 0, 1, 0, 1],  // interlace_pass == 7
]

// LOW_BIT_DEPTH_MULTIPLIERS holds multipliers that convert D-bit values into
// 8-bit values, for depth D.
pri const LOW_BIT_DEPTH_MULTIPLIERS : array[8] base.u8 = [
	0,
	0b1111_1111,  // depth == 1
	0b0101_0101,  // depth == 2
	0,
	0b0001_0001,  // depth == 4
	0,
	0,
	0,
]

// LOW_BIT_DEPTH_NUM_PACKS holds the number of smaller-than-1-byte units that
// are packed into each byte.
pri const LOW_BIT_DEPTH_NUM_PACKS : array[8] base.u8 = [
	0,
	8,  // depth == 1
	4,  // depth == 2
	0,
	2,  // depth == 4
	0,
	0,
	0,
]

// NUM_CHANNELS holds the number of channels for each valid color type.
pri const NUM_CHANNELS : array[8] base.u8[..= 4] = [
	1,  // color_type == 0: Y
	0,
	3,  // color_type == 2: RGB
	1,  // color_type == 3: indexed
	2,  // color_type == 4: YA
	0,
	4,  // color_type == 6: RGBA
	0,
]