Re: Animated gif patch

Andy Piper <andy(a)xemacs.org&gt; writes: It is in a graphics control extension block together with transparency (which you probably need to implement for optimized animations). If I read gifrlib.h and the specification[1] correctly for such a SavedImage the Function member must be == GRAPHICS_EXT_FUNC_CODE and then ExtensionBlockCount should be 1, ExtensionBlocks[0].ByteCount should be 4 and ExtensionBlocks[0].Bytes is an array of lengh 4 that contain byte 1-4 from the block as given in the specification (see below). i.e. the delay should be ((unsigned)Bytes[2] << 8) + Bytes[1] in 1/100's of a second. In addition seem indicate netscape has its own extensions for looping :-( http://lxr.mozilla.org/seamonkey/source/modules/libimg/gifcom/gif.cpp#549 1 | | | | | <Packed Fields> See below +---------------+ 2 | | Delay Time Unsigned +- -+ 3 | | +---------------+ 4 | | Transparent Color Index Byte +---------------+ <Packed Fields> = Reserved 3 Bits Disposal Method 3 Bits User Input Flag 1 Bit Transparent Color Flag 1 Bit i) Extension Introducer - Identifies the beginning of an extension ii) Graphic Control Label - Identifies the current block as a Graphic Control Extension. This field contains the fixed value 0xF9. iii) Block Size - Number of bytes in the block, after the Block Size field and up to but not including the Block Terminator. This field contains the fixed value 4. iv) Disposal Method - Indicates the way in which the graphic is to be treated after being displayed. Values : 0 - No disposal specified. The decoder is not required to take any action. 1 - Do not dispose. The graphic is to be left in place. 2 - Restore to background color. The area used by the graphic must be restored to the background color. 3 - Restore to previous. The decoder is required to restore the area overwritten by the graphic with what was there prior to rendering the graphic. 4-7 - To be defined. v) User Input Flag - Indicates whether or not user input is expected before continuing. If the flag is set, processing will continue when user input is entered. The nature of the User input is determined by the application (Carriage Return, Mouse Button Click, etc.). Values : 0 - User input is not expected. 1 - User input is expected. When a Delay Time is used and the User Input Flag is set, processing will continue when user input is received or when the delay time expires, whichever occurs first. vi) Transparency Flag - Indicates whether a transparency index is given in the Transparent Index field. (This field is the least significant bit of the byte.) Values : 0 - Transparent Index is not given. 1 - Transparent Index is given. vii) Delay Time - If not 0, this field specifies the number of hundredths (1/100) of a second to wait before continuing with the processing of the Data Stream. The clock starts ticking immediately after the graphic is rendered. This field may be used in conjunction with the User Input Flag field. viii) Transparency Index - The Transparency Index is such that when encountered, the corresponding pixel of the display device is not modified and processing goes on to the next pixel. The index is present if and only if the Transparency Flag is set to 1. Footnotes: [1] http://members.aol.com/royalef/gif89a.txt