GIF Images

Animated GIF File Decoder

GIF files can be one frame or animated images made up of many frames that are displayed at a set frame rate. The following program allows you to view either kind of image or use them in a program. _LOADIMAGE can only return one frame of an animated image.

NOTE: Include the FILELIST$ (function) or create your own File INPUT routine!

'####################################################################################### '# Animated GIF decoder v1.0 # '# By Zom-B # '####################################################################################### DEFINT A-Z '$DYNAMIC DIM SHARED Dbg: Dbg = 0 DIM SHARED powerOf2&(11) FOR a = 0 TO 11: powerOf2&(a) = 2 ^ a: NEXT a TYPE GIFDATA file AS INTEGER sigver AS STRING * 6 width AS _UNSIGNED INTEGER height AS _UNSIGNED INTEGER bpp AS _UNSIGNED _BYTE sortFlag AS _BYTE ' Unused colorRes AS _UNSIGNED _BYTE colorTableFlag AS _BYTE bgColor AS _UNSIGNED _BYTE aspect AS SINGLE ' Unused numColors AS _UNSIGNED INTEGER palette AS STRING * 768 END TYPE TYPE FRAMEDATA addr AS LONG left AS _UNSIGNED INTEGER top AS _UNSIGNED INTEGER width AS _UNSIGNED INTEGER height AS _UNSIGNED INTEGER localColorTableFlag AS _BYTE interlacedFlag AS _BYTE sortFlag AS _BYTE ' Unused palBPP AS _UNSIGNED _BYTE minimumCodeSize AS _UNSIGNED _BYTE transparentFlag AS _BYTE 'GIF89a-specific (animation) values userInput AS _BYTE ' Unused disposalMethod AS _UNSIGNED _BYTE delay AS SINGLE transColor AS _UNSIGNED _BYTE END TYPE SCREEN _NEWIMAGE(640, 480, 32) ' Open gif file. This reads the headers and palette but not the image data. ' The array will be redimentioned to fit the exact number of frames in the file. DIM gifData AS GIFDATA, frameData(0 TO 0) AS FRAMEDATA filename$ = "mygif.gif" '<<<<<<<<<<<< Enter a file name here!!! IF LEN(filename$) = 0 THEN END openGif filename$, gifData, frameData() ' Loop away. frame = 0 DO ' Request a frame. If it has been requested before, it is re-used, ' otherwise it is read and decoded from the file. _PUTIMAGE (0, 0), getGifFrame&(gifData, frameData(), frame) _DELAY frameData(frame).delay frame = (frame + 1) MOD (UBOUND(framedata) + 1) LOOP UNTIL LEN(INKEY$) 'Close the file and free the allocated frames. codeGif gifData, frameData() END '######################################################################################## SUB openGif (filename$, gifData AS GIFDATA, frameData() AS FRAMEDATA) STATIC file = FREEFILE: gifData.file = file OPEN "B", gifData.file, filename$ GET file, , gifData.sigver GET file, , gifData.width GET file, , gifData.height GET file, , byte~%% gifData.bpp = (byte~%% AND 7) + 1 gifData.sortFlag = (byte~%% AND 8) > 0 gifData.colorRes = (byte~%% \ 16 AND 7) + 1 gifData.colorTableFlag = (byte~%% AND 128) > 0 gifData.numColors = 2 ^ gifData.bpp GET file, , gifData.bgColor GET file, , byte~%% IF byte~%% = 0 THEN gifData.aspect = 0 ELSE gifData.aspect = (byte~%% + 15) / 64 IF gifData.sigver <> "GIF87a" AND gifData.sigver <> "GIF89a" THEN _DEST 0: PRINT "Invalid version": END IF NOT gifData.colorTableFlag THEN _DEST 0: PRINT "No Color Table": END palette$ = SPACE$(3 * gifData.numColors) GET file, , palette$ gifData.palette = palette$ IF Dbg AND 1 THEN PRINT "sigver ="; gifData.sigver PRINT "width ="; gifData.width PRINT "height ="; gifData.height PRINT "bpp ="; gifData.bpp PRINT "sortFlag ="; gifData.sortFlag PRINT "colorRes ="; gifData.colorRes PRINT "colorTableFlag ="; gifData.colorTableFlag PRINT "bgColor ="; gifData.bgColor PRINT "aspect ="; gifData.aspect PRINT "numColors ="; gifData.numColors FOR i = 0 TO gifData.numColors - 1 PRINT USING "pal(###) = "; i; PRINT HEX$(_RGB32(ASC(gifData.palette, i * 3 + 1), ASC(gifData.palette, i * 3 + 2), ASC(gifData.palette, i * 3 + 3))) NEXT END IF DO GET file, , byte~%% IF Dbg AND 2 THEN PRINT "Chunk: "; HEX$(byte~%%) SELECT CASE byte~%% CASE &H2C ' Image Descriptor IF frame > UBOUND(frameData) THEN REDIM _PRESERVE frameData(0 TO frame * 2 - 1) AS FRAMEDATA END IF GET file, , frameData(frame).left GET file, , frameData(frame).top GET file, , frameData(frame).width GET file, , frameData(frame).height GET file, , byte~%% frameData(frame).localColorTableFlag = (byte~%% AND 128) > 0 frameData(frame).interlacedFlag = (byte~%% AND 64) > 0 frameData(frame).sortFlag = (byte~%% AND 32) > 0 frameData(frame).palBPP = (byte~%% AND 7) + 1 frameData(frame).addr = LOC(file) + 1 IF frameData(frame).localColorTableFlag THEN SEEK file, LOC(file) + 3 * 2 ^ frameData(frame).palBPP + 1 END IF GET file, , frameData(frame).minimumCodeSize IF Dbg AND 2 THEN PRINT "addr ="; HEX$(frameData(frame).addr - 1) PRINT "left ="; frameData(frame).left PRINT "top ="; frameData(frame).top PRINT "width ="; frameData(frame).width PRINT "height ="; frameData(frame).height PRINT "localColorTableFlag ="; frameData(frame).localColorTableFlag PRINT "interlacedFlag ="; frameData(frame).interlacedFlag PRINT "sortFlag ="; frameData(frame).sortFlag PRINT "palBPP ="; frameData(frame).palBPP PRINT "minimumCodeSize ="; frameData(frame).minimumCodeSize END IF IF localColors THEN _DEST 0: PRINT "Local color table": END IF frameData(frame).disposalMethod > 2 THEN PRINT "Unsupported disposalMethod: "; frameData(frame).disposalMethod: END skipBlocks file frame = frame + 1 CASE &H3B ' Trailer EXIT DO CASE &H21 ' Extension Introducer GET file, , byte~%% ' Extension Label IF Dbg AND 2 THEN PRINT "Extension Introducer: "; HEX$(byte~%%) SELECT CASE byte~%% CASE &HFF, &HFE ' Application Extension, Comment Extension skipBlocks file CASE &HF9 IF frame > UBOUND(frameData) THEN REDIM _PRESERVE frameData(0 TO frame * 2 - 1) AS FRAMEDATA END IF GET 1, , byte~%% ' Block Size (always 4) GET 1, , byte~%% frameData(frame).transparentFlag = (byte~%% AND 1) > 0 frameData(frame).userInput = (byte~%% AND 2) > 0 frameData(frame).disposalMethod = byte~%% \ 4 AND 7 GET 1, , delay~% IF delay~% = 0 THEN frameData(frame).delay = 0.1 ELSE frameData(frame).delay = delay~% / 100 GET 1, , frameData(frame).transColor IF Dbg AND 2 THEN PRINT "frame ="; frame PRINT "transparentFlag ="; frameData(frame).transparentFlag PRINT "userInput ="; frameData(frame).userInput PRINT "disposalMethod ="; frameData(frame).disposalMethod PRINT "delay ="; frameData(frame).delay PRINT "transColor ="; frameData(frame).transColor END IF skipBlocks file CASE ELSE PRINT "Unsupported extension Label: "; HEX$(byte~%%): END END SELECT CASE ELSE PRINT "Unsupported chunk: "; HEX$(byte~%%): END END SELECT LOOP REDIM _PRESERVE frameData(0 TO frame - 1) AS FRAMEDATA END FUNCTION SUB skipBlocks (file) DO GET file, , byte~%% ' Block Size IF Dbg AND 2 THEN PRINT "block size ="; byte~%% SEEK file, LOC(file) + byte~%% + 1 LOOP WHILE byte~%% END SUB FUNCTION getGifFrame& (gifData AS GIFDATA, frameData() AS FRAMEDATA, frame) IF frameData(frame).addr > 0 THEN IF Dbg AND 4 THEN PRINT "addr ="; HEX$(frameData(frame).addr - 1) PRINT "left ="; frameData(frame).left PRINT "top ="; frameData(frame).top PRINT "width ="; frameData(frame).width PRINT "height ="; frameData(frame).height PRINT "localColorTableFlag ="; frameData(frame).localColorTableFlag PRINT "interlacedFlag ="; frameData(frame).interlacedFlag PRINT "sortFlag ="; frameData(frame).sortFlag PRINT "palBPP ="; frameData(frame).palBPP PRINT "minimumCodeSize ="; frameData(frame).minimumCodeSize PRINT "transparentFlag ="; frameData(frame).transparentFlag PRINT "userInput ="; frameData(frame).userInput PRINT "disposalMethod ="; frameData(frame).disposalMethod PRINT "delay ="; frameData(frame).delay PRINT "transColor ="; frameData(frame).transColor END IF w = frameData(frame).width h = frameData(frame).height img& = _NEWIMAGE(w, h, 256) frame& = _NEWIMAGE(gifData.width, gifData.height, 256) _DEST img& decodeFrame gifData, frameData(frame) _DEST frame& IF frameData(frame).localColorTableFlag THEN _COPYPALETTE img& ELSE FOR i = 0 TO gifData.numColors - 1 _PALETTECOLOR i, _RGB32(ASC(gifData.palette, i * 3 + 1), ASC(gifData.palette, i * 3 + 2), ASC(gifData.palette, i * 3 + 3)) NEXT END IF IF frame THEN SELECT CASE frameData(frame - 1).disposalMethod CASE 0, 1 _PUTIMAGE , frameData(frame - 1).addr CASE 2 CLS , gifData.bgColor _CLEARCOLOR gifData.bgColor END SELECT ELSE CLS , gifData.bgColor END IF IF frameData(frame).transparentFlag THEN _CLEARCOLOR frameData(frame).transColor, img& END IF _PUTIMAGE (frameData(frame).left, frameData(frame).top), img& _FREEIMAGE img& frameData(frame).addr = frame& _DEST 0 END IF getGifFrame& = frameData(frame).addr END FUNCTION '############################################################################################ SUB decodeFrame (gifdata AS GIFDATA, framedata AS FRAMEDATA) DIM byte AS _UNSIGNED _BYTE DIM prefix(4095), suffix(4095), colorStack(4095) startCodeSize = gifdata.bpp + 1 clearCode = 2 ^ gifdata.bpp endCode = clearCode + 1 minCode = endCode + 1 startMaxCode = clearCode * 2 - 1 nvc = minCode codeSize = startCodeSize maxCode = startMaxCode IF framedata.interlacedFlag THEN interlacedPass = 0: interlacedStep = 8 bitPointer = 0 blockSize = 0 blockPointer = 0 x = 0 y = 0 file = gifdata.file SEEK file, framedata.addr IF framedata.localColorTableFlag THEN palette$ = SPACE$(3 * 2 ^ framedata.palBPP) GET 1, , palette$ FOR i = 0 TO gifdata.numColors - 1 c& = _RGB32(ASC(palette$, i * 3 + 1), ASC(palette$, i * 3 + 2), ASC(palette$, i * 3 + 3)) _PALETTECOLOR i, c& NEXT END IF GET file, , byte ' minimumCodeSize DO GOSUB GetCode stackPointer = 0 IF code = clearCode THEN 'Reset & Draw next color direct nvc = minCode ' \ codeSize = startCodeSize ' Preset default codes maxCode = startMaxCode ' / GOSUB GetCode currentCode = code lastColor = code colorStack(stackPointer) = lastColor stackPointer = 1 ELSEIF code <> endCode THEN 'Draw direct color or colors from suffix currentCode = code IF currentCode = nvc THEN 'Take last color too currentCode = oldCode colorStack(stackPointer) = lastColor stackPointer = stackPointer + 1 END IF WHILE currentCode >= minCode 'Extract colors from suffix colorStack(stackPointer) = suffix(currentCode) stackPointer = stackPointer + 1 currentCode = prefix(currentCode) 'Next color from suffix is described in WEND ' the prefix, else prefix is the last col. lastColor = currentCode ' Last color is equal to the colorStack(stackPointer) = lastColor ' last known code (direct, or from stackPointer = stackPointer + 1 ' Prefix) suffix(nvc) = lastColor 'Automatically, update suffix prefix(nvc) = oldCode 'Code from the session before (for extracting from suffix) nvc = nvc + 1 IF nvc > maxCode AND codeSize < 12 THEN codeSize = codeSize + 1 maxCode = maxCode * 2 + 1 END IF END IF FOR i = stackPointer - 1 TO 0 STEP -1 PSET (x, y), colorStack(i) x = x + 1 IF x = framedata.width THEN x = 0 IF framedata.interlacedFlag THEN y = y + interlacedStep IF y >= framedata.height THEN SELECT CASE interlacedPass CASE 0: interlacedPass = 1: y = 4 CASE 1: interlacedPass = 2: y = 2 CASE 2: interlacedPass = 3: y = 1 END SELECT interlacedStep = 2 * y END IF ELSE y = y + 1 END IF END IF NEXT oldCode = code LOOP UNTIL code = endCode GET file, , byte EXIT SUB GetCode: IF bitPointer = 0 THEN GOSUB ReadByteFromBlock: bitPointer = 8 WorkCode& = LastChar \ powerOf2&(8 - bitPointer) WHILE codeSize > bitPointer GOSUB ReadByteFromBlock WorkCode& = WorkCode& OR LastChar * powerOf2&(bitPointer) bitPointer = bitPointer + 8 WEND bitPointer = bitPointer - codeSize code = WorkCode& AND maxCode RETURN ReadByteFromBlock: IF blockPointer = blockSize THEN GET file, , byte: blockSize = byte a$ = SPACE$(blockSize): GET file, , a$ blockPointer = 0 END IF blockPointer = blockPointer + 1 LastChar = ASC(MID$(a$, blockPointer, 1)) RETURN END SUB SUB codeGif (gifData AS GIFDATA, frameData() AS FRAMEDATA) FOR i = 0 TO UBOUND(FRAMEDATA) IF frameData(i).addr < 0 THEN _FREEIMAGE frameData(i).addr NEXT CLOSE gifData.file END SUB

NOTE: If full code is not displayed then refresh browser.

Using with $INCLUDE: 'FILELIST$.BM' File

Copy the code from the FILELIST$ (function) or FILELIST$ page to a text file named _FILE$.BM and use when compiling. Just save with .BM extension (Save As ALL files) in Notepad or other text editor. The file is not necessary after the program is compiled.

See also

• GIF Creation, Bitmaps
• Icons and Cursors
• _LOADIMAGE, _PUTIMAGE
• FILELIST$ (function) (member file search routine)
• SaveIcon32 (create icons from any image)
• $EXEICON (Icon visible in Windows Explorer)

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