Changes between Initial Version and Version 1 of Develop/FileFormats/GIF

Timestamp:

Dec 11, 2018, 1:04:27 PM (5 years ago)

Author:

Thomas Bernard

Comment:

add GIF doc

Develop/FileFormats/GIF

@@ +1 @@
+==  GRAPHICS INTERCHANGE FORMAT
+
+GrafX2 format of predilection is GIF.
+
+GrafX2 uses the GIF89a spec for saving :
+https://www.w3.org/Graphics/GIF/spec-gif89a.txt
+
+it supports a few extensions :
+* NETSCAPE animation extension
+* GFX2PATH original path saving extension
+* GFX2MODE Special Drawing mode saving extension
+* CRNG     Color cycling extension
+
+
+== NETSCAPE animation extension
+see http://www.vurdalakov.net/misc/gif/netscape-looping-application-extension
+
+== GFX2PATH
+Stores the original file path.
+This is used by the backup system.
+
+The format is :
+
+{{{
+0x21       Extension Label
+0xFF       Application Extension Label
+0x0B       Block Size
+"GFX2PATH" Application Identifier (8 bytes)
+"\0\0\0"   Application Authentication Code (3 bytes)
+0xll       Sub-block Data Size : path size (including null)
+"..path.." path (null-terminated)
+0xll       Sub-block Data Size : filename size (including null)
+"..file.." file name (null-terminated)
+0x00       Block terminator
+}}}
+
+== GFX2MODE
+extension to store ::IMAGE_MODES :
+
+{{{
+
+0x21       Extension Label
+0xFF       Application Extension Label
+0x0B       Block Size
+"GFX2MODE" Application Identifier (8 bytes)
+"2.6"      Application Authentication Code (3 bytes)
+0xll       Sub-block Data Size
+string     label
+...        More sub blocks can be added in the future
+0x00 Block terminator
+}}}
+
+Supported values (as of GrafX2 2.6) :
+* "LAYERED" (not written)
+* "ANIMATION" (not written)
+* "ZX_SPECTRUM"
+* "GAMEBOYCOLOR"
+* "THOMSON40COL"
+* "CPC_EGX"
+* "CPC_EGX2"
+* "CPC_MODE5"
+* "CPC_RASTER"
+* "C64_HIRES"
+* "C64_MULTICOLOR"
+* "C64_FLI"
+* "APPLE2_HGR"
+* "APPLE2_DHGR"
+
+== CRNG color cycling extension
+Same content as a CRNG [wiki:Develop/FileFormats/IFF IFF] chunk
+
+
+{{{
+0x21       Extension Label
+0xFF       Application Extension Label
+0x0B       Block Size
+"CRNG\0\0\0\0" "CRNG" Application Identifier (8 bytes)
+"1.0"      Application Authentication Code (3 bytes)
+0xll       Sub-block Data Size (6 bytes per color cycle)
+For each color cycle :
+  0xRRRR   (big endian) Rate
+  0xFFFF   (big endian) Flags
+  0xSS     start (lower color index)
+  0xEE     end (higher color index)
+0x00       Block terminator
+
+}}}
+