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422 lines
14 KiB
Markdown
422 lines
14 KiB
Markdown
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**Animated GIF File Decoder**
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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](_LOADIMAGE) can only return one frame of an animated image.
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```vb
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'#######################################################################################
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'# Animated GIF decoder v1.0 #
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'# By Zom-B #
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'#######################################################################################
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DEFINT A-Z
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'$DYNAMIC
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DIM SHARED Dbg: Dbg = 0
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DIM SHARED powerOf2&(11)
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FOR a = 0 TO 11: powerOf2&(a) = 2 ^ a: NEXT a
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TYPE GIFDATA
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file AS INTEGER
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sigver AS STRING * 6
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width AS _UNSIGNED INTEGER
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height AS _UNSIGNED INTEGER
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bpp AS _UNSIGNED _BYTE
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sortFlag AS _BYTE ' Unused
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colorRes AS _UNSIGNED _BYTE
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colorTableFlag AS _BYTE
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bgColor AS _UNSIGNED _BYTE
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aspect AS SINGLE ' Unused
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numColors AS _UNSIGNED INTEGER
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palette AS STRING * 768
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END TYPE
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TYPE FRAMEDATA
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addr AS LONG
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left AS _UNSIGNED INTEGER
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top AS _UNSIGNED INTEGER
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width AS _UNSIGNED INTEGER
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height AS _UNSIGNED INTEGER
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localColorTableFlag AS _BYTE
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interlacedFlag AS _BYTE
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sortFlag AS _BYTE ' Unused
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palBPP AS _UNSIGNED _BYTE
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minimumCodeSize AS _UNSIGNED _BYTE
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transparentFlag AS _BYTE 'GIF89a-specific (animation) values
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userInput AS _BYTE ' Unused
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disposalMethod AS _UNSIGNED _BYTE
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delay AS SINGLE
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transColor AS _UNSIGNED _BYTE
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END TYPE
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SCREEN _NEWIMAGE(640, 480, 32)
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' Open gif file. This reads the headers and palette but not the image data.
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' The array will be redimentioned to fit the exact number of frames in the file.
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DIM gifData AS GIFDATA, frameData(0 TO 0) AS FRAMEDATA
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filename$ = "mygif.gif" '<<<<<<<<<<<< Enter a file name here!!!
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IF LEN(filename$) = 0 THEN END
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openGif filename$, gifData, frameData()
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' Loop away.
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frame = 0
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DO
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' Request a frame. If it has been requested before, it is re-used,
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' otherwise it is read and decoded from the file.
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_PUTIMAGE (0, 0), getGifFrame&(gifData, frameData(), frame)
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_DELAY frameData(frame).delay
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frame = (frame + 1) MOD (UBOUND(framedata) + 1)
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LOOP UNTIL LEN(INKEY$)
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'Close the file and free the allocated frames.
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codeGif gifData, frameData()
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END
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'########################################################################################
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SUB openGif (filename$, gifData AS GIFDATA, frameData() AS FRAMEDATA) STATIC
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file = FREEFILE: gifData.file = file
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OPEN "B", gifData.file, filename$
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GET file, , gifData.sigver
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GET file, , gifData.width
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GET file, , gifData.height
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GET file, , byte~%%
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gifData.bpp = (byte~%% AND 7) + 1
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gifData.sortFlag = (byte~%% AND 8) > 0
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gifData.colorRes = (byte~%% \ 16 AND 7) + 1
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gifData.colorTableFlag = (byte~%% AND 128) > 0
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gifData.numColors = 2 ^ gifData.bpp
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GET file, , gifData.bgColor
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GET file, , byte~%%
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IF byte~%% = 0 THEN gifData.aspect = 0 ELSE gifData.aspect = (byte~%% + 15) / 64
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IF gifData.sigver <> "GIF87a" AND gifData.sigver <> "GIF89a" THEN _DEST 0: PRINT "Invalid version": END
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IF NOT gifData.colorTableFlag THEN _DEST 0: PRINT "No Color Table": END
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palette$ = SPACE$(3 * gifData.numColors)
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GET file, , palette$
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gifData.palette = palette$
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IF Dbg AND 1 THEN
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PRINT "sigver ="; gifData.sigver
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PRINT "width ="; gifData.width
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PRINT "height ="; gifData.height
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PRINT "bpp ="; gifData.bpp
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PRINT "sortFlag ="; gifData.sortFlag
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PRINT "colorRes ="; gifData.colorRes
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PRINT "colorTableFlag ="; gifData.colorTableFlag
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PRINT "bgColor ="; gifData.bgColor
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PRINT "aspect ="; gifData.aspect
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PRINT "numColors ="; gifData.numColors
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FOR i = 0 TO gifData.numColors - 1
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PRINT USING "pal(###) = "; i;
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PRINT HEX$(_RGB32(ASC(gifData.palette, i * 3 + 1), ASC(gifData.palette, i * 3 + 2), ASC(gifData.palette, i * 3 + 3)))
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NEXT
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END IF
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DO
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GET file, , byte~%%
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IF Dbg AND 2 THEN PRINT "Chunk: "; HEX$(byte~%%)
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SELECT CASE byte~%%
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CASE &H2C ' Image Descriptor
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IF frame > UBOUND(frameData) THEN
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REDIM _PRESERVE frameData(0 TO frame * 2 - 1) AS FRAMEDATA
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END IF
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GET file, , frameData(frame).left
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GET file, , frameData(frame).top
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GET file, , frameData(frame).width
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GET file, , frameData(frame).height
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GET file, , byte~%%
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frameData(frame).localColorTableFlag = (byte~%% AND 128) > 0
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frameData(frame).interlacedFlag = (byte~%% AND 64) > 0
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frameData(frame).sortFlag = (byte~%% AND 32) > 0
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frameData(frame).palBPP = (byte~%% AND 7) + 1
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frameData(frame).addr = LOC(file) + 1
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IF frameData(frame).localColorTableFlag THEN
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SEEK file, LOC(file) + 3 * 2 ^ frameData(frame).palBPP + 1
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END IF
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GET file, , frameData(frame).minimumCodeSize
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IF Dbg AND 2 THEN
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PRINT "addr ="; HEX$(frameData(frame).addr - 1)
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PRINT "left ="; frameData(frame).left
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PRINT "top ="; frameData(frame).top
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PRINT "width ="; frameData(frame).width
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PRINT "height ="; frameData(frame).height
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PRINT "localColorTableFlag ="; frameData(frame).localColorTableFlag
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PRINT "interlacedFlag ="; frameData(frame).interlacedFlag
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PRINT "sortFlag ="; frameData(frame).sortFlag
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PRINT "palBPP ="; frameData(frame).palBPP
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PRINT "minimumCodeSize ="; frameData(frame).minimumCodeSize
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END IF
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IF localColors THEN _DEST 0: PRINT "Local color table": END
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IF frameData(frame).disposalMethod > 2 THEN PRINT "Unsupported disposalMethod: "; frameData(frame).disposalMethod: END
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skipBlocks file
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frame = frame + 1
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CASE &H3B ' Trailer
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EXIT DO
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CASE &H21 ' Extension Introducer
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GET file, , byte~%% ' Extension Label
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IF Dbg AND 2 THEN PRINT "Extension Introducer: "; HEX$(byte~%%)
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SELECT CASE byte~%%
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CASE &HFF, &HFE ' Application Extension, Comment Extension
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skipBlocks file
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CASE &HF9
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IF frame > UBOUND(frameData) THEN
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REDIM _PRESERVE frameData(0 TO frame * 2 - 1) AS FRAMEDATA
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END IF
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GET 1, , byte~%% ' Block Size (always 4)
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GET 1, , byte~%%
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frameData(frame).transparentFlag = (byte~%% AND 1) > 0
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frameData(frame).userInput = (byte~%% AND 2) > 0
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frameData(frame).disposalMethod = byte~%% \ 4 AND 7
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GET 1, , delay~%
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IF delay~% = 0 THEN frameData(frame).delay = 0.1 ELSE frameData(frame).delay = delay~% / 100
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GET 1, , frameData(frame).transColor
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IF Dbg AND 2 THEN
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PRINT "frame ="; frame
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PRINT "transparentFlag ="; frameData(frame).transparentFlag
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PRINT "userInput ="; frameData(frame).userInput
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PRINT "disposalMethod ="; frameData(frame).disposalMethod
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PRINT "delay ="; frameData(frame).delay
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PRINT "transColor ="; frameData(frame).transColor
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END IF
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skipBlocks file
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CASE ELSE
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PRINT "Unsupported extension Label: "; HEX$(byte~%%): END
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END SELECT
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CASE ELSE
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PRINT "Unsupported chunk: "; HEX$(byte~%%): END
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END SELECT
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LOOP
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REDIM _PRESERVE frameData(0 TO frame - 1) AS FRAMEDATA
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END FUNCTION
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SUB skipBlocks (file)
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DO
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GET file, , byte~%% ' Block Size
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IF Dbg AND 2 THEN PRINT "block size ="; byte~%%
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SEEK file, LOC(file) + byte~%% + 1
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LOOP WHILE byte~%%
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END SUB
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FUNCTION getGifFrame& (gifData AS GIFDATA, frameData() AS FRAMEDATA, frame)
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IF frameData(frame).addr > 0 THEN
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IF Dbg AND 4 THEN
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PRINT "addr ="; HEX$(frameData(frame).addr - 1)
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PRINT "left ="; frameData(frame).left
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PRINT "top ="; frameData(frame).top
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PRINT "width ="; frameData(frame).width
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PRINT "height ="; frameData(frame).height
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PRINT "localColorTableFlag ="; frameData(frame).localColorTableFlag
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PRINT "interlacedFlag ="; frameData(frame).interlacedFlag
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PRINT "sortFlag ="; frameData(frame).sortFlag
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PRINT "palBPP ="; frameData(frame).palBPP
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PRINT "minimumCodeSize ="; frameData(frame).minimumCodeSize
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PRINT "transparentFlag ="; frameData(frame).transparentFlag
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PRINT "userInput ="; frameData(frame).userInput
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PRINT "disposalMethod ="; frameData(frame).disposalMethod
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PRINT "delay ="; frameData(frame).delay
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PRINT "transColor ="; frameData(frame).transColor
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END IF
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w = frameData(frame).width
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h = frameData(frame).height
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img& = _NEWIMAGE(w, h, 256)
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frame& = _NEWIMAGE(gifData.width, gifData.height, 256)
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_DEST img&
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decodeFrame gifData, frameData(frame)
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_DEST frame&
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IF frameData(frame).localColorTableFlag THEN
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_COPYPALETTE img&
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ELSE
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FOR i = 0 TO gifData.numColors - 1
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_PALETTECOLOR i, _RGB32(ASC(gifData.palette, i * 3 + 1), ASC(gifData.palette, i * 3 + 2), ASC(gifData.palette, i * 3 + 3))
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NEXT
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END IF
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IF frame THEN
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SELECT CASE frameData(frame - 1).disposalMethod
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CASE 0, 1
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_PUTIMAGE , frameData(frame - 1).addr
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CASE 2
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CLS , gifData.bgColor
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_CLEARCOLOR gifData.bgColor
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END SELECT
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ELSE
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CLS , gifData.bgColor
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END IF
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IF frameData(frame).transparentFlag THEN
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_CLEARCOLOR frameData(frame).transColor, img&
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END IF
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_PUTIMAGE (frameData(frame).left, frameData(frame).top), img&
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_FREEIMAGE img&
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frameData(frame).addr = frame&
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_DEST 0
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END IF
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getGifFrame& = frameData(frame).addr
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END FUNCTION
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'############################################################################################
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SUB decodeFrame (gifdata AS GIFDATA, framedata AS FRAMEDATA)
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DIM byte AS _UNSIGNED _BYTE
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DIM prefix(4095), suffix(4095), colorStack(4095)
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startCodeSize = gifdata.bpp + 1
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clearCode = 2 ^ gifdata.bpp
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endCode = clearCode + 1
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minCode = endCode + 1
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startMaxCode = clearCode * 2 - 1
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nvc = minCode
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codeSize = startCodeSize
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maxCode = startMaxCode
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IF framedata.interlacedFlag THEN interlacedPass = 0: interlacedStep = 8
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bitPointer = 0
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blockSize = 0
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blockPointer = 0
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x = 0
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y = 0
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file = gifdata.file
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SEEK file, framedata.addr
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IF framedata.localColorTableFlag THEN
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palette$ = SPACE$(3 * 2 ^ framedata.palBPP)
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GET 1, , palette$
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FOR i = 0 TO gifdata.numColors - 1
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c& = _RGB32(ASC(palette$, i * 3 + 1), ASC(palette$, i * 3 + 2), ASC(palette$, i * 3 + 3))
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_PALETTECOLOR i, c&
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NEXT
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END IF
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GET file, , byte ' minimumCodeSize
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DO
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GOSUB GetCode
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stackPointer = 0
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IF code = clearCode THEN 'Reset & Draw next color direct
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nvc = minCode ' \
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codeSize = startCodeSize ' Preset default codes
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maxCode = startMaxCode ' /
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GOSUB GetCode
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currentCode = code
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lastColor = code
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colorStack(stackPointer) = lastColor
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stackPointer = 1
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ELSEIF code <> endCode THEN 'Draw direct color or colors from suffix
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currentCode = code
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IF currentCode = nvc THEN 'Take last color too
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currentCode = oldCode
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colorStack(stackPointer) = lastColor
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stackPointer = stackPointer + 1
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END IF
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WHILE currentCode >= minCode 'Extract colors from suffix
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colorStack(stackPointer) = suffix(currentCode)
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stackPointer = stackPointer + 1
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currentCode = prefix(currentCode) 'Next color from suffix is described in
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WEND ' the prefix, else prefix is the last col.
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lastColor = currentCode ' Last color is equal to the
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colorStack(stackPointer) = lastColor ' last known code (direct, or from
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stackPointer = stackPointer + 1 ' Prefix)
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suffix(nvc) = lastColor 'Automatically, update suffix
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prefix(nvc) = oldCode 'Code from the session before (for extracting from suffix)
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nvc = nvc + 1
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IF nvc > maxCode AND codeSize < 12 THEN
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codeSize = codeSize + 1
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maxCode = maxCode * 2 + 1
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END IF
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END IF
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FOR i = stackPointer - 1 TO 0 STEP -1
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PSET (x, y), colorStack(i)
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x = x + 1
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IF x = framedata.width THEN
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x = 0
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IF framedata.interlacedFlag THEN
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y = y + interlacedStep
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IF y >= framedata.height THEN
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SELECT CASE interlacedPass
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CASE 0: interlacedPass = 1: y = 4
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CASE 1: interlacedPass = 2: y = 2
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CASE 2: interlacedPass = 3: y = 1
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END SELECT
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interlacedStep = 2 * y
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END IF
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ELSE
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y = y + 1
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END IF
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END IF
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NEXT
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oldCode = code
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LOOP UNTIL code = endCode
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GET file, , byte
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EXIT SUB
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GetCode:
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IF bitPointer = 0 THEN GOSUB ReadByteFromBlock: bitPointer = 8
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WorkCode& = LastChar \ powerOf2&(8 - bitPointer)
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WHILE codeSize > bitPointer
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GOSUB ReadByteFromBlock
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WorkCode& = WorkCode& OR LastChar * powerOf2&(bitPointer)
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bitPointer = bitPointer + 8
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WEND
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bitPointer = bitPointer - codeSize
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code = WorkCode& AND maxCode
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RETURN
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ReadByteFromBlock:
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IF blockPointer = blockSize THEN
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GET file, , byte: blockSize = byte
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a$ = SPACE$(blockSize): GET file, , a$
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blockPointer = 0
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END IF
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blockPointer = blockPointer + 1
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LastChar = ASC(MID$(a$, blockPointer, 1))
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RETURN
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END SUB
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SUB codeGif (gifData AS GIFDATA, frameData() AS FRAMEDATA)
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FOR i = 0 TO UBOUND(FRAMEDATA)
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IF frameData(i).addr < 0 THEN _FREEIMAGE frameData(i).addr
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NEXT
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CLOSE gifData.file
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END SUB
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```
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NOTE: This has been reported to only work using 256-color images, and you need to keep the code loading into a 32-bit image destination as the source?
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## See Also
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* [GIF Creation](GIF-Creation), [Bitmaps](Bitmaps)
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* [Icons and Cursors](Icons-and-Cursors)
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* [_LOADIMAGE](_LOADIMAGE), [_PUTIMAGE](_PUTIMAGE)
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* [FILELIST$ (function)](FILELIST$-(function)) (member file search routine)
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* [SaveIcon32](SaveIcon32) (create icons from any image)
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* [$EXEICON]($EXEICON) (Icon visible in Windows Explorer)
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