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1syntax = "proto2";
2// Proto description of the gif format.
3// Refer to: https://www.fileformat.info/format/gif/egff.htm
4// https://www.matthewflickinger.com/lab/whatsinagif/bits_and_bytes.asp
5
6// TODO: Verify if this is correct
7
8message LogicalScreenDescriptor {
9    required uint32 ScreenWidth = 1;
10    required uint32 ScreenHeight= 2;
11    required uint32 Packed = 3;
12    required uint32 BackgroundColor = 4;
13    required uint32 AspectRatio = 5;
14}
15
16message GlobalColorTable {
17    required bytes colors = 1;
18}
19
20message ImageDescriptor {
21  required uint32 Seperator =1;
22  required uint32 Left =2;
23  required uint32 Top = 3;
24  required uint32 Width = 4;
25  required uint32 Height = 5;
26  required uint32 Packed = 6;
27}
28
29message GraphicControlExtension {
30  required uint32 Packed = 1;
31  required uint32 DelayTime = 2;
32  required uint32 transparentColorIndex = 3;
33}
34
35message PlainTextExtension {
36  repeated SubBlock subs = 1;
37  optional GraphicControlExtension gcExt = 2;
38}
39
40message LocalColorTable {
41  required bytes colors = 1;
42}
43
44message SubBlock {
45  required uint32 len = 1;
46  required bytes data = 2;
47}
48
49message ImageData {
50  required uint32 lzw = 1;
51  repeated SubBlock subs = 2;
52}
53
54message BasicChunk {
55  required ImageDescriptor imDescriptor =1;
56  required LocalColorTable lct = 2;
57  required ImageData img = 3;
58  optional GraphicControlExtension gcExt = 4;
59}
60
61message ApplicationExtension {
62  required fixed64 appid = 1;
63  repeated SubBlock subs = 2;
64}
65
66message CommentExtension {
67  repeated SubBlock subs = 1;
68}
69
70message Header {
71  enum Version {
72    ENA = 1;
73    ESA = 2;
74    INV = 3;
75  }
76  required Version ver = 1;
77}
78
79message Trailer {}
80
81message ImageChunk {
82  oneof chunk_oneof {
83    BasicChunk basic = 1;
84    PlainTextExtension plaintext = 2;
85    ApplicationExtension appExt = 3;
86    CommentExtension comExt = 4;
87  }
88}
89
90message GifProto {
91  required Header header = 1;
92  required LogicalScreenDescriptor lsd = 2;
93  // Instead of making GCT optional here, we condition its visit on LSD's packed byte
94  // in the converter
95  required GlobalColorTable gct = 3;
96  repeated ImageChunk chunks = 4;
97  required Trailer trailer = 5;
98}
99
100package gifProtoFuzzer;