From f730d8b0ccfd457b2c80183b5c1b412137d9c28f Mon Sep 17 00:00:00 2001
From: Minei3oat <Minei3oat@users.noreply.github.com>
Date: Wed, 28 Dec 2022 10:47:11 +0100
Subject: [PATCH] patterns/gif: Added GIF pattern (#67)

patterns/gif: Added GIF pattern
---
 README.md           |   1 +
 patterns/gif.hexpat | 153 ++++++++++++++++++++++++++++++++++++++++++++
 2 files changed, 154 insertions(+)
 create mode 100644 patterns/gif.hexpat

diff --git a/README.md b/README.md
index 0691093..0107418 100644
--- a/README.md
+++ b/README.md
@@ -57,6 +57,7 @@ Hex patterns, include patterns and magic files for the use with the ImHex Hex Ed
 | PFS0 | | [`patterns/pfs0.hexpat`](patterns/pfs0.hexpat) | Nintendo Switch PFS0 archive (NSP files) |
 | XCI | | [`patterns/xci.hexpat`](patterns/xci.hexpat) | Nintendo Switch XCI cardridge ROM |
 | WAD | | [`patterns/wad.hexpat`](patterns/wad.hexpat) | DOOM WAD Archive |
+| GIF | `image/gif` | [`patterns/gif.hexpat`](patterns/gif.hexpat) | GIF image files |
 
 ### Scripts
 
diff --git a/patterns/gif.hexpat b/patterns/gif.hexpat
new file mode 100644
index 0000000..d9ccaa4
--- /dev/null
+++ b/patterns/gif.hexpat
@@ -0,0 +1,153 @@
+#include <std/mem.pat>
+
+#pragma MIME image/gif
+
+#pragma bitfield_order left_to_right
+
+// gif89a
+
+struct data_subblock_t {
+    u8 block_size;
+    u8 data_values[block_size];
+};
+
+struct data_subblocks_t {
+    data_subblock_t data[while (std::mem::read_unsigned($, 1) != 0x00)];
+    u8 block_terminator;        // 0x00
+} [[inline]];
+
+struct header_t {
+    char header[3];
+    char version[3];
+};
+
+bitfield lsd_fields_t {
+    global_color_table_flag : 1;
+    color_resolution        : 3;
+    sort_flag               : 1;
+    size_of_global_color_table : 3;
+} [[inline]];
+
+struct logical_screen_descriptor_t {
+    u16 width;
+    u16 height;
+    lsd_fields_t fields;
+    u8 background_color_index;
+    u8 pixel_aspect_ratio;
+};
+
+struct color_table_entry_t {
+    u8 red;
+    u8 green;
+    u8 blue;
+};
+
+bitfield gce_fields_t {
+    padding         : 3;
+    disposal_method : 3;
+    user_input_flag : 1;
+    transparent_color_flag : 1;
+} [[inline]];
+
+struct graphic_coltrol_extension_t {
+    u8 extension_introducer;    // 0x21
+    u8 graphic_control_label;   // 0xf9
+    u8 block_size;
+    gce_fields_t fields;
+    u16 delay_time;
+    u8 transparent_color_index;
+    u8 block_terminator;
+};
+
+struct comment_extension_t {
+    u8 extension_introducer;    // 0x21
+    u8 comment_label;           // 0xfe
+    data_subblocks_t comment_data;
+};
+
+struct plaintext_extension_t {
+    u8 extension_introducer;    // 0x21
+    u8 plain_text_label;        // 0x01
+
+    u8 block_size;              // 12
+    u16 text_grid_left_position;
+    u16 text_grid_top_position;
+    u16 text_grid_width;
+    u16 text_grid_height;
+    u8 character_cell_width;
+    u8 character_cell_height;
+    u8 text_foreground_color_index;
+    u8 text_background_color_index;
+    data_subblocks_t plain_text_data;
+};
+
+struct application_extension_t {
+    u8 extension_introducer;    // 0x21
+    u8 extension_label;         // 0xff
+
+    u8 block_size;              // 11
+    u8 application_identifier[8];
+    u8 application_authentication_code[3];
+    
+    data_subblocks_t data;
+};
+
+bitfield id_fields_t {
+    local_color_table : 1;
+    interlace_flag    : 1;
+    sort_fla          : 1;
+    padding           : 2;
+    size_of_local_color_table : 3;
+} [[inline]];
+
+struct image_descriptor_t {
+    u8 image_separator;         // 0x2c
+    u16 image_left_position;
+    u16 image_top_position;
+    u16 image_width;
+    u16 image_height;
+    id_fields_t fields;
+};
+
+struct table_based_image_t {
+    u8 lzw_minimum_code_size;
+    data_subblocks_t data;
+};
+
+struct gif_block_t {
+    if (std::mem::read_unsigned($, 1) == 0x21) {
+        if (std::mem::read_unsigned($+1, 1) == 0x01) {
+            plaintext_extension_t plaintext_extension;
+        }
+        else if (std::mem::read_unsigned($+1, 1) == 0xf9) {
+            graphic_coltrol_extension_t graphic_coltrol_extension;
+        }
+        else if (std::mem::read_unsigned($+1, 1) == 0xfe) {
+            comment_extension_t comment;
+        } else {
+            application_extension_t application_extension;
+        }
+    }
+    else if (std::mem::read_unsigned($, 1) == 0x2c) {
+        image_descriptor_t image_descriptor;
+        if (image_descriptor.fields.local_color_table) {
+            color_table_entry_t local_color_table[1<<(image_descriptor.fields.size_of_local_color_table + 1)];
+        }
+        table_based_image_t image;
+    }
+} [[inline]];
+
+struct gif_t {
+    header_t header;
+    logical_screen_descriptor_t logical_screen_descriptor;
+    if (logical_screen_descriptor.fields.global_color_table_flag) {
+        color_table_entry_t global_color_table[1<<(logical_screen_descriptor.fields.size_of_global_color_table + 1)];
+    }
+    
+    gif_block_t blocks[while (std::mem::read_unsigned($, 1) != 0x3b)];
+
+    u8 trailer;                 // 0x3b
+};
+
+gif_t gif @ 0x00;
+