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05-01-2022, 05:22 AM
(This post was last modified: 05-01-2022, 05:27 AM by SMcNeill.)
Code: (Select All) '%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%GIF STUFF%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
DIM SHARED MakeGif_OutBuffer AS STRING
DIM SHARED MakeGif_OStartAddress AS INTEGER, MakeGif_OAddress AS INTEGER
DIM SHARED MakeGif_OEndAddress AS INTEGER, MakeGif_OSeg AS INTEGER
DIM SHARED MakeGif_CodeSize AS INTEGER, MakeGif_CurrnetBit AS INTEGER, MakeGif_Char AS LONG
DIM SHARED MakeGIF_BlockLength AS INTEGER, MakeGif_X AS INTEGER, MakeGif_Y AS INTEGER
DIM SHARED MakeGif_MinX AS INTEGER, MakeGif_MinY AS INTEGER
DIM SHARED MakeGif_MaxX AS INTEGER, MakeGif_MaxY AS INTEGER
DIM SHARED MakeGif_Done AS INTEGER, MakeGif_GIFfile AS INTEGER, MakeGif_LastLoc AS LONG
'%%%%%%%%%%%%%%%%%%%%%%%%%%%END OF GIF STUFF%%%%%%%%%%%%%%%%%%%%%%%%%%%%
DIM Demo_T
SCREEN _NEWIMAGE(640, 480, 256)
RANDOMIZE TIMER
FOR i = 1 TO 100
LINE (RND * 640, RND * 480)-(RND * 640, RND * 480), i, BF 'draw some junk on the screen
NEXT
SaveGIF "booga.gif", 0, 0, 0, 639, 479
SLEEP
CLS
SLEEP
Demo_T = _LOADIMAGE("booga.gif")
SCREEN Demo_T
'%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%GIF STUFF%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
'-----------------------------------------------------------------------
' PDS 7.1 & QB4.5 GIF Compression Routine v1.00 By Rich Geldreich 1992
' Bug fixed and Overhauled for QB64 by Steve McNeill 2019
'-----------------------------------------------------------------------
SUB SaveGIF (file$, image AS LONG, Xstart, YStart, Xend, Yend)
CONST Table.Size = 7177 'hash table's size - must be a prime number!
'Variables all DIMMED so as to avoid any OPTION _EXPLICIT errors.
DIM Prefix(Table.Size - 1) AS INTEGER
DIM Suffix(Table.Size - 1) AS INTEGER
DIM code(Table.Size - 1) AS INTEGER
DIM ScreenX AS INTEGER
DIM ScreenY AS INTEGER
DIM B AS STRING
DIM NumColors AS INTEGER
DIM BitsPixel AS INTEGER
DIM StartSize AS INTEGER
DIM StartCode AS INTEGER
DIM StartMax AS INTEGER
DIM ColorBits AS INTEGER
DIM a1 AS INTEGER
DIM a AS STRING
DIM R AS INTEGER
DIM G AS INTEGER
DIM B1 AS INTEGER
DIM ImageWidth AS INTEGER
DIM ImageHeight AS INTEGER
DIM MaxCode AS INTEGER
DIM ClearCode AS INTEGER
DIM EOFCode AS INTEGER
DIM NextCode AS INTEGER
DIM a2 AS LONG
DIM Prefix AS INTEGER
DIM Suffix AS INTEGER
DIM Found AS INTEGER
DIM index AS INTEGER
DIM Offset AS INTEGER
DIM D AS INTEGER
DIM S AS INTEGER
D = _DEST: S = _SOURCE
_DEST image&: _SOURCE image&
'MakeGif_MinX, MakeGif_MinY, MakeGif_MaxX, MakeGif_MaxY have the encoding window
ScreenX = _WIDTH: ScreenY = _HEIGHT
MakeGif_MinX = Xstart: MakeGif_MinY = YStart
MakeGif_MaxX = Xend: MakeGif_MaxY = Yend
'Open GIF output file
MakeGif_GIFfile = FREEFILE 'use next free file
OPEN file$ FOR BINARY AS MakeGif_GIFfile
'Put GIF87a header at beginning of file
B$ = "GIF87a"
PUT MakeGif_GIFfile, , B$
'See how many colors are in this image...
NumColors = 256 'who cares about the old school graphic modes with fewer colors? Not me! Find a different encoder. :)
BitsPixel = 8 '8 bits per pixel
StartSize = 9 'first LZW code is 9 bits
StartCode = 256 'first free code
StartMax = 512 'maximum code in 9 bits
ColorBits = 6 'VGA
PUT MakeGif_GIFfile, , ScreenX 'put screen's dimensions
PUT MakeGif_GIFfile, , ScreenY
'pack colorbits and bits per pixel
a1 = 215 ' precalculated value: for 128 + (ColorBits - 1) * 16 + (BitsPixel - 1)
PUT MakeGif_GIFfile, , a1
'throw a zero into the GIF file; reserved for future expansion of format (which will never come)
a$ = CHR$(0)
PUT MakeGif_GIFfile, , a$
'Get the RGB palette from the screen and put it into the file...
FOR a1 = 0 TO 255
'Note: a BIOS call could be used here, but then we have to use
'the messy CALL INTERRUPT subs...
R = _RED(a1, image&)
G = _GREEN(a1, image&)
B1 = _BLUE(a1, image&)
a$ = CHR$(R): PUT MakeGif_GIFfile, , a$
a$ = CHR$(G): PUT MakeGif_GIFfile, , a$
a$ = CHR$(B1): PUT MakeGif_GIFfile, , a$
NEXT
'write out an image descriptor...
a$ = "," '"," is image seperator
PUT MakeGif_GIFfile, , a$ 'write it
PUT MakeGif_GIFfile, , MakeGif_MinX 'write out the image's location
PUT MakeGif_GIFfile, , MakeGif_MinY
ImageWidth = (MakeGif_MaxX - MakeGif_MinX + 1) 'find length & width of image
ImageHeight = (MakeGif_MaxY - MakeGif_MinY + 1)
PUT MakeGif_GIFfile, , ImageWidth 'store them into the file
PUT MakeGif_GIFfile, , ImageHeight
a$ = CHR$(BitsPixel - 1) '# bits per pixel in the image
PUT MakeGif_GIFfile, , a$
a$ = CHR$(StartSize - 1) 'store the LZW minimum code size
PUT MakeGif_GIFfile, , a$
'Initialize the vars needed by PutCode
MakeGif_CurrnetBit = 0: MakeGif_Char = 0
MaxCode = StartMax 'the current maximum code size
MakeGif_CodeSize = StartSize 'the current code size
ClearCode = StartCode 'ClearCode & EOF code are the
EOFCode = StartCode + 1 ' first two entries
StartCode = StartCode + 2 'first free code that can be used
NextCode = StartCode 'the current code
MakeGif_OutBuffer = STRING$(5000, 32) 'output buffer; for speedy disk writes
a2& = SADD(MakeGif_OutBuffer) 'find address of buffer
a2& = a2& - 65536 * (a2& < 0)
MakeGif_OSeg = VARSEG(MakeGif_OutBuffer) + (a2& \ 16) 'get segment + offset >> 4
MakeGif_OAddress = a2& AND 15 'get address into segment
MakeGif_OEndAddress = MakeGif_OAddress + 5000 'end of disk buffer
MakeGif_OStartAddress = MakeGif_OAddress 'current location in disk buffer
DEF SEG = MakeGif_OSeg
FOR a1 = 0 TO Table.Size - 1 'clears the hashing table
Prefix(a1) = -1 '-1 = invalid entry
Suffix(a1) = -1
code(a1) = -1
NEXT
PutCode ClearCode ' clear code
MakeGif_X = Xstart: MakeGif_Y = YStart 'MakeGif_X & MakeGif_Y have the current pixel
Prefix = GetByte 'the first pixel is a special case
MakeGif_Done = 0 '-1 when image is complete
DO 'while there are more pixels to encode
DO 'until we have a new string to put into the table
'get a pixel from the screen and see if we can find
'the new string in the table
Suffix = GetByte
GOSUB Hash 'is it there?
IF Found = -1 THEN Prefix = code(index) 'yup, replace the
'prefix:suffix string with whatever
'code represents it in the table
LOOP WHILE Found AND NOT MakeGif_Done 'don't stop unless we find a new string
PutCode Prefix 'output the prefix to the file
Prefix(index) = Prefix 'put the new string in the table
Suffix(index) = Suffix
code(index) = NextCode 'we've got to keep track if what code this is!
Prefix = Suffix 'Prefix=the last pixel pulled from the screen
NextCode = NextCode + 1 'get ready for the next code
IF NextCode = MaxCode + 1 THEN 'can an output code ever exceed
'the current code size?
'yup, increase the code size
MaxCode = MaxCode * 2
'Note: The GIF89a spec mentions something about a deferred clear
'code. When the clear code is deferred, codes are not entered
'into the hash table anymore. When the compression of the image
'starts to fall below a certain threshold, the clear code is
'sent and the hash table is cleared. The overall result is
'greater compression, because the table is cleared less often.
'This version of MakeGIF doesn't support this, because some GIF
'decoders crash when they attempt to enter too many codes
'into the string table.
IF MakeGif_CodeSize = 12 THEN 'is the code size too big?
PutCode ClearCode 'yup; clear the table and
FOR a1 = 0 TO Table.Size - 1 'clears the hashing table
Prefix(a1) = -1 '-1 = invalid entry
Suffix(a1) = -1
code(a1) = -1
NEXT
NextCode = StartCode
MakeGif_CodeSize = StartSize
MaxCode = StartMax
ELSE
MakeGif_CodeSize = MakeGif_CodeSize + 1 'just increase the code size if
END IF 'it's not too high( not > 12)
END IF
LOOP UNTIL MakeGif_Done 'while we have more pixels
'Once MakeGif_Done, write out the last pixel, clear the disk buffer
'and fix up the last block so its count is correct
PutCode Prefix 'write last pixel
PutCode EOFCode 'send EOF code
IF MakeGif_CurrnetBit <> 0 THEN
PutCode 0 'flush out the last code...
END IF
PutByte 0
MakeGif_OutBuffer = LEFT$(MakeGif_OutBuffer, MakeGif_OAddress - MakeGif_OStartAddress)
PUT MakeGif_GIFfile, , MakeGif_OutBuffer
a$ = ";" + STRING$(8, &H1A) 'the 8 EOF chars is not standard,
'but many GIF's have them, so how
'much could it hurt?
PUT MakeGif_GIFfile, , a$
a$ = CHR$(255 - MakeGIF_BlockLength) 'correct the last block's count
PUT MakeGif_GIFfile, MakeGif_LastLoc, a$
CLOSE MakeGif_GIFfile
_DEST D: _SOURCE S 'restore the destination and source now that we're done.
EXIT SUB 'so we won't have any issues trying to run the hash routines below.
'this is only one of a plethora of ways to search the table for
'a match! I used a binary tree first, but I switched to hashing
'cause it's quicker(perhaps the way I implemented the tree wasn't
'optimal... who knows!)
Hash:
'hash the prefix & suffix(there are also many ways to do this...)
'?? is there a better formula?
index = ((Prefix * 256&) XOR Suffix) MOD Table.Size
'
'(Note: the table size(7177 in this case) must be a prime number, or
'else there's a chance that the routine will hang up... hate when
'that happens!)
'
'Calculate an offset just in case we don't find what we want on the
'first try...
IF index = 0 THEN 'can't have Table.Size-0 !
Offset = 1
ELSE
Offset = Table.Size - index
END IF
DO 'until we (1) find an empty entry or (2) find what we're lookin for
IF code(index) = -1 THEN 'is this entry blank?
Found = 0 'yup- we didn't find the string
RETURN
'is this entry the one we're looking for?
ELSEIF Prefix(index) = Prefix AND Suffix(index) = Suffix THEN
'yup, congrats you now understand hashing!!!
Found = -1
RETURN
ELSE
'shoot! we didn't find anything interesting, so we must
'retry- this is what slows hashing down. I could of used
'a bigger table, that would of speeded things up a little
'because this retrying would not happen as often...
index = index - Offset
IF index < 0 THEN 'too far down the table?
'wrap back the index to the end of the table
index = index + Table.Size
END IF
END IF
LOOP
END SUB
'Puts a byte into the GIF file & also takes care of each block.
SUB PutByte (a) STATIC
MakeGIF_BlockLength = MakeGIF_BlockLength - 1 'are we at the end of a block?
IF MakeGIF_BlockLength <= 0 THEN ' yup,
MakeGIF_BlockLength = 255 'block length is now 255
MakeGif_LastLoc = LOC(MakeGif_GIFfile) + 1 + (MakeGif_OAddress - MakeGif_OStartAddress) 'remember the pos.
BufferWrite 255 'for later fixing
END IF
BufferWrite a 'put a byte into the buffer
END SUB
'Puts an LZW variable-bit code into the output file...
SUB PutCode (a) STATIC
MakeGif_Char = MakeGif_Char + a * 2 ^ MakeGif_CurrnetBit 'put the char were it belongs;
MakeGif_CurrnetBit = MakeGif_CurrnetBit + MakeGif_CodeSize ' shifting it to its proper place
DO WHILE MakeGif_CurrnetBit > 7 'do we have a least one full byte?
PutByte MakeGif_Char AND 255 ' yup! mask it off and write it out
MakeGif_Char = MakeGif_Char \ 256 'shift the bit buffer right 8 bits
MakeGif_CurrnetBit = MakeGif_CurrnetBit - 8 'now we have 8 less bits
LOOP 'until we don't have a full byte
END SUB
SUB BufferWrite (a) STATIC
IF MakeGif_OAddress = MakeGif_OEndAddress THEN 'are we at the end of the buffer?
PUT MakeGif_GIFfile, , MakeGif_OutBuffer ' yup, write it out and
MakeGif_OAddress = MakeGif_OStartAddress ' start all over
END IF
POKE MakeGif_OAddress, a 'put byte in buffer
MakeGif_OAddress = MakeGif_OAddress + 1 'increment position
END SUB
'This routine gets one pixel from the display.
FUNCTION GetByte STATIC
GetByte = POINT(MakeGif_X, MakeGif_Y) 'get the "byte"
MakeGif_X = MakeGif_X + 1 'increment MakeGif_X coordinate
IF MakeGif_X > MakeGif_MaxX THEN 'are we too far?
MakeGif_X = MakeGif_MinX 'go back to start
MakeGif_Y = MakeGif_Y + 1 'increment MakeGif_Y coordinate
IF MakeGif_Y > MakeGif_MaxY THEN 'are we too far down?
MakeGif_Done = -1 ' yup, flag it then
END IF
END IF
END FUNCTION
'%%%%%%%%%%%%%%%%%%%%%%%%%%%END OF GIF STUFF%%%%%%%%%%%%%%%%%%%%%%%%%%%%
So, having the original to work with now, I started playing around with what would be needed to speed it up a bit and make it faster for us in QB64, while working to keep all the comments to help others understand what's going on inside the code. I took out several of the old OUT statements and replaced them with a much simpler _RED, _GREEN, _BLUE version of things. I explicitedly dimmed all the variables so they wouldn't cause any issues with OPTION _EXPLICIT. Fixed a glitch where it was checking the LOC(1) and not the LOC(GIFfile)....
A few tweaks here, a few minor changes there, a lot of DIM work.. and I now have the version posted above, which I thought I'd share for whomever might be interested in studying and learning the GIF format from.
Posts: 1,507
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And the raw, unedited version of Rich's work is here:
Code: (Select All) DEFINT A-Z
DECLARE FUNCTION GetByte% ()
DECLARE SUB BufferWrite (a%)
DECLARE SUB MakeGif (a$, ScreenX%, ScreenY%, Xstart%, YStart%, Xend%,Yend%, NumColors%, AdaptorType%)
DECLARE SUB PutByte (a%)
DECLARE SUB PutCode (a%)
DECLARE SUB pal (c%, R%, G%, B%)
CONST TRUE = -1, FALSE = NOT TRUE
'GS3DO.BAS by Matt Bross, 1997
'The sorting algorithm was originally written by Ryan Wellman, which I
'modified for my own purposes. I made the 3D program with help from
'3D tutorials by Lithium /VLA, Shade3D.BAS by Rich Geldreich; and
'Gouraud fill with Luke Molnar's (of M/K Productions) gorau.bas. The GIF
'support is from Rich Geldreich's MakeGif.BAS.
'
'completely RANDOMIZE
RANDOMIZE TIMER: DO: RANDOMIZE TIMER: LOOP UNTIL RND > .5
'ON ERROR GOTO ErrorHandler
TYPE PointType
x AS SINGLE 'X coordinate
y AS SINGLE 'Y coordinate
z AS SINGLE 'Z coordinate
shade AS INTEGER 'shade of points
dis AS SINGLE 'distance from the origin (0, 0, 0)
END TYPE
TYPE PolyType
C1 AS INTEGER 'number of the first point of a polygon
C2 AS INTEGER 'number of the second point of a polygon
C3 AS INTEGER 'number of the third point of a polygon
culled AS INTEGER 'TRUE if the polygon isn't visible
AvgZ AS INTEGER 'used to sort Z coordinates of polygons
END TYPE
TYPE FillType
Y1 AS INTEGER 'starting Y coordinate
Y2 AS INTEGER 'ending Y coordinate
clr1 AS INTEGER 'starting color
clr2 AS INTEGER 'ending color
END TYPE
'%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%INFO%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
SCREEN 0, 0, 0, 0: WIDTH 80, 25: CLS
PRINT "GS3DO.BAS by Matt Bross, 1997"
PRINT
PRINT "3D ANIMATION FOR THE QBASIC LANGUAGE"
PRINT "COPYRIGHT MATT BROSS. USE FREELY AS"
PRINT "LONG AS CREDIT IS GIVEN."
PRINT
PRINT "--------CONTROLS--------"
PRINT " 0 - reset rotation"
PRINT " 5 - stop rotation"
PRINT " S - reset location"
PRINT " A - stop translation"
PRINT "2, 8 - rotate around x axis"
PRINT "4, 6 - rotate around y axis"
PRINT "-, + - rotate around z axis"
PRINT CHR$(24); ", "; CHR$(25); " - translate vertically"
PRINT CHR$(27); ", "; CHR$(26); " - translate horizontally"
PRINT "Z, X - translate depthwise"
PRINT " Esc - exit"
PRINT "----CASE INSENSITIVE----"
PRINT
INPUT "OBJECT TO LOAD", file$
IF file$ = "" THEN file$ = "pyramid.txt"
'%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%VARIABLES%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
'SRX = the screen's x resolution
'SRY = the screen's y resolution
SRX = 320: SRY = 200
'DX = the X coordinate of the center of the screen
'DY = the Y coordinate of the center of the screen
DX = SRX \ 2: DY = SRY \ 2
'D = the viewer's distance then object: SD = controls perspective
D = 350: SD = 140
'MaxSpin = controls the maximum rotation speed
'MaxSpeed = controls the maximum translation speed
MaxSpin = 20: MaxSpeed = 10
'NumClr = the number of palette values to assign to shading each color
NumClr = 63
'%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%GIF STUFF%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
DIM SHARED OutBuffer$, OStartAddress, OAddress, OEndAddress, Oseg
DIM SHARED CodeSize, CurrentBit, Char&, BlockLength
DIM SHARED Shift(7) AS LONG
DIM SHARED x, y, Minx, MinY, MaxX, MaxY, Done, GIFFile, LastLoc&
ShiftTable:
DATA 1,2,4,8,16,32,64,128
'%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%SIN TABLES%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
'create SINe and COSine tables for 360 degrees in radians, and then
'scale 1024 times for faster math.
'$STATIC
DIM SINx(360) AS LONG, COSx(360) AS LONG
FOR i = 0 TO 360
SINx(i) = SIN(i * (22 / 7) / 180) * 1024 'use 1024 to shift binary digits
COSx(i) = COS(i * (22 / 7) / 180) * 1024 'over 6 bits.
NEXT i
'%%%%%%%%%%%%%%%%%%%%%%%%%%GOURAUD SHADE ARRAYS%%%%%%%%%%%%%%%%%%%%%%%%%
DIM scan(320) AS FillType 'DIM gouraud shading array
DIM coord(1 TO 3)
'%%%%%%%%%%%%%%%%%%%%%%%%DOUBLE BUFFERING ARRAYS%%%%%%%%%%%%%%%%%%%%%%%%
DIM SHARED aofs&
DIM SHARED ScnBuf(32001) 'DIM array to serve as page in SCREEN 13
ScnBuf(0) = 320 * 8 'set length (x)
ScnBuf(1) = 200 'set height (y)
DEF SEG = VARSEG(ScnBuf(2)) 'get segment of beginning of array data
aofs& = VARPTR(ScnBuf(2)) 'get offset of beginning of array data
'%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%LIGHT TABLES%%%%%%%%%%%%%%%%%%%%%%%%%%%%
DIM LX(256), LY(256), LZ(256)
'Location of light source in spherical coordinates
l1 = 70: l2 = 40: a1! = l1 / 57.29: a2! = l2 / 57.29
s1! = SIN(a1!): C1! = COS(a1!): s2! = SIN(a2!): C2! = COS(a2!)
LX = 128 * s1! * C2!: LY = 128 * s1! * s2!: LZ = 128 * C1!
'find length of segment from light source to origin (0, 0, 0)
ldis! = SQR(LX * LX + LY * LY + LZ * LZ) / 128
FOR a = -128 TO 128
LX(a + 128) = LX * a 'make light source lookup tables for shading
LY(a + 128) = LY * a
LZ(a + 128) = LZ * a
NEXT a
'%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%LOAD OBJECT%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
OPEN file$ FOR INPUT AS #1
'Load Points Data
INPUT #1, MaxPoints, MaxPolys
DIM POINTS(MaxPoints) AS PointType 'at start
DIM ScnPnts(MaxPoints) AS PointType 'after rotation
DIM SX(MaxPoints), SY(MaxPoints) 'points drawn to screen
FOR i = 1 TO MaxPoints
INPUT #1, x!, y!, z!: POINTS(i).x = x!: POINTS(i).y = y!: POINTS(i).z = z!
'find distance from point to the origin (0, 0, 0)
dis! = SQR(x! * x! + y! * y! + z! * z!)
POINTS(i).dis = dis! * ldis!: ScnPnts(i).dis = dis! * ldis!
NEXT i
'Load Polygon Data
DIM SHARED P(MaxPolys) AS PolyType 'stores all polygon data
FOR i = 1 TO MaxPolys
INPUT #1, P(i).C1, P(i).C2, P(i).C3
NEXT i: CLOSE
PRINT "Press a Key"
DO: LOOP UNTIL INKEY$ <> ""
'%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%SET PALETTE%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
SCREEN 13: CLS
s! = 0: ClrStep! = 63 / NumClr
FOR a = 0 TO NumClr
pal a, c, c, c
s! = s! + ClrStep!: c = INT(s!)
NEXT a
'%%%%%%%%%%%%%%%%%%%%%%%%%%%LOOK UP VARIABLES%%%%%%%%%%%%%%%%%%%%%%%%%%%
ZERO = 0: ONE = 1: THREE6D = 360
'------------------------------>BEGIN MAIN LOOP<------------------------
DO
'*********************************GET KEY*******************************
k$ = UCASE$(INKEY$)
SELECT CASE k$
CASE "0"
R1 = ZERO: R2 = ZERO: R3 = ZERO
D1 = ZERO: D2 = ZERO: D3 = ZERO
CASE "5"
D1 = ZERO: D2 = ZERO: D3 = ZERO
CASE "A"
MX = ZERO: MY = ZERO: MZ = ZERO
CASE "S"
MX = ZERO: MY = ZERO: MZ = ZERO
MMX = ZERO: MMY = ZERO: MMZ = ZERO
CASE "2"
D1 = D1 - ONE
CASE "8"
D1 = D1 + ONE
CASE "4"
D2 = D2 - ONE
CASE "6"
D2 = D2 + ONE
CASE "+", "="
D3 = D3 - ONE
CASE "-"
D3 = D3 + ONE
CASE CHR$(0) + "H"
MY = MY + ONE
CASE CHR$(0) + "P"
MY = MY - ONE
CASE CHR$(0) + "K"
MX = MX + ONE
CASE CHR$(0) + "M"
MX = MX - ONE
CASE "Z"
MZ = MZ + ONE
CASE "X"
MZ = MZ - ONE
CASE CHR$(27)
GOTO ShutDown
CASE "G"
file$ = "pyramid.gif"
IF RIGHT$(UCASE$(file$), 4) <> ".GIF" THEN file$ = file$ + ".GIF"
PUT (0, 0), ScnBuf(), PSET
MakeGif file$, 320, 200, 0, 0, 319, 199, 256, 2
END SELECT
'*********************************ROTATION******************************
'keep rotation speed under control
IF D1 > MaxSpin THEN D1 = MaxSpin
IF D2 > MaxSpin THEN D2 = MaxSpin
IF D2 > MaxSpin THEN D2 = MaxSpin
IF D1 < -MaxSpin THEN D1 = -MaxSpin
IF D2 < -MaxSpin THEN D2 = -MaxSpin
IF D2 < -MaxSpin THEN D2 = -MaxSpin
'keep SINes and COSines in array limits
R1 = (R1 + D1) MOD THREE6D: IF R1 < ZERO THEN R1 = THREE6D + R1
R2 = (R2 + D2) MOD THREE6D: IF R2 < ZERO THEN R2 = THREE6D + R2
R3 = (R3 + D3) MOD THREE6D: IF R3 < ZERO THEN R3 = THREE6D + R3
'********************************TRANSLATION****************************
'Keep translation speed from becoming uncontrollable
IF MX > MaxSpeed THEN MX = MaxSpeed
IF MY > MaxSpeed THEN MY = MaxSpeed
IF MZ > MaxSpeed THEN MZ = MaxSpeed
IF MX < -MaxSpeed THEN MX = -MaxSpeed
IF MY < -MaxSpeed THEN MY = -MaxSpeed
IF MZ < -MaxSpeed THEN MZ = -MaxSpeed
MMX = MMX + MX: MMY = MMY + MY: MMZ = MMZ + MZ
'Keeps variables within limits of integers
IF MMX > 32767 THEN MMX = 32767
IF MMY > 250 THEN MMY = 250
IF MMZ > 120 THEN MMZ = 120
IF MMX < -32767 THEN MMX = -32767
IF MMY < -120 THEN MMY = -120
IF MMZ < -327 THEN MMZ = -327
'*******************************MOVE OBJECT*****************************
FOR i = 1 TO MaxPoints
'rotate points around the Y axis
TEMPX = (POINTS(i).x * COSx(R2) - POINTS(i).z * SINx(R2)) \ 1024
TEMPZ = (POINTS(i).x * SINx(R2) + POINTS(i).z * COSx(R2)) \ 1024
'rotate points around the X axis
ScnPnts(i).z = (TEMPZ * COSx(R1) - POINTS(i).y * SINx(R1)) \ 1024
TEMPY = (TEMPZ * SINx(R1) + POINTS(i).y * COSx(R1)) \ 1024
'rotate points around the Z axis
ScnPnts(i).x = (TEMPX * COSx(R3) + TEMPY * SINx(R3)) \ 1024
ScnPnts(i).y = (TEMPY * COSx(R3) - TEMPX * SINx(R3)) \ 1024
'******************************CONVERT 3D TO 2D*************************
TEMPZ = ScnPnts(i).z + MMZ - SD
IF TEMPZ < ZERO THEN 'only calculate points visible by viewer
SX(i) = (D * ((ScnPnts(i).x + MMX) / TEMPZ)) + DX
SY(i) = (D * ((ScnPnts(i).y + MMY) / TEMPZ)) + DY
END IF
'*******************************SHADE POINTS****************************
X1 = ScnPnts(i).x: Y1 = ScnPnts(i).y: Z1 = ScnPnts(i).z
s = CINT((X1 * LX + Y1 * LY + Z1 * LZ) \ ScnPnts(i).dis) + 128
IF s < ZERO THEN s = ZERO
IF s > 256 THEN s = 256
shade = (LX(s) + LY(s) + LZ(s)) \ 3
IF shade < ZERO THEN shade = ZERO
IF shade > NumClr THEN shade = NumClr
ScnPnts(i).shade = shade
NEXT
FOR i = 1 TO MaxPolys
'*************************CULL NON-VISIABLE POLYGONS********************
'this isn't perfect yet so I REMmed it, so for more speed unrem the following
coord(1) = P(i).C1: coord(2) = P(i).C2: coord(3) = P(i).C3
X1 = ScnPnts(coord(1)).x: X2 = ScnPnts(coord(2)).x: X3 = ScnPnts(coord(3)).x
Y1 = ScnPnts(coord(1)).y: Y2 = ScnPnts(coord(2)).y: Y3 = ScnPnts(coord(3)).y
Z1 = ScnPnts(coord(1)).z: Z2 = ScnPnts(coord(2)).z: Z3 = ScnPnts(coord(3)).z
cull1 = X3 * ((Y1 * Z2) - (Z1 * Y2)): cull2 = Y3 * ((X1 * Z2) - (Z1 * X2))
cull3 = Z3 * ((X1 * Y2) - (Y1 * X2))
IF cull1 + cull2 + cull3 = ZERO THEN P(i).culled = TRUE ELSE P(i).culled = FALSE
'******************FIND AVERAGE Z COORDINATE OF EACH POLYGON************
P(i).AvgZ = (Z1 + Z2 + Z3) \ 3
NEXT i
'******************SORT POLGONS BY THEIR AVERAGE Z COORDINATE***********
increment = MaxPolys + 1
DO
increment = increment \ 2
FOR index = 1 TO MaxPolys - increment
IF P(index).AvgZ > P(index + increment).AvgZ THEN
SWAP P(index), P(index + increment)
IF index > increment THEN
cutpoint = index
DO
index = (index - increment): IF index < 1 THEN index = 1
IF P(index).AvgZ > P(index + increment).AvgZ THEN
SWAP P(index), P(index + increment)
ELSE
index = cutpoint: EXIT DO
END IF
LOOP
END IF
END IF
NEXT index
LOOP UNTIL increment <= 1
'******************************DRAW POLYGONS****************************
'clear screen buffer. Use a 320 by 200 BLOADable graphic for a background.
ERASE ScnBuf: ScnBuf(0) = 2560: ScnBuf(1) = SRY
FOR i = 1 TO MaxPolys
IF P(i).culled = FALSE THEN
'load points
coord(1) = P(i).C1: coord(2) = P(i).C2: coord(3) = P(i).C3
'find highest and lowest Y coordinates
xmin = SRX: xmax = ZERO
IF SX(coord(1)) > xmax THEN xmax = SX(coord(1))
IF SX(coord(2)) > xmax THEN xmax = SX(coord(2))
IF SX(coord(3)) > xmax THEN xmax = SX(coord(3))
IF SX(coord(1)) < xmin THEN xmin = SX(coord(1))
IF SX(coord(2)) < xmin THEN xmin = SX(coord(2))
IF SX(coord(3)) < xmin THEN xmin = SX(coord(3))
'keep min's and max's in the limits of the screen
IF xmin < ZERO THEN xmin = ZERO
IF xmax > SRX THEN xmax = SRX
IF xmin > SRX THEN EXIT FOR
IF xmax < ZERO THEN EXIT FOR
IF SY(coord(1)) AND SY(coord(2)) AND SY(coord(3)) < ZERO THEN EXIT FOR
IF SY(coord(1)) AND SY(coord(2)) AND SY(coord(3)) > SRY THEN EXIT FOR
ERASE scan
FOR j = 1 TO 3
k = j + 1: IF k > 3 THEN k = 1
VAL1 = coord(j): VAL2 = coord(k)
IF SX(VAL1) > SX(VAL2) THEN SWAP VAL1, VAL2
Y1 = SY(VAL1): X1 = SX(VAL1): Y2 = SY(VAL2): X2 = SX(VAL2)
col1 = ScnPnts(VAL1).shade: Col2 = ScnPnts(VAL2).shade
XDelta = X2 - X1: YDelta = Y2 - Y1: CDelta = Col2 - col1
IF XDelta <> ZERO THEN
YSlope = (YDelta / XDelta) * 128
CSlope = (CDelta / XDelta) * 128
ELSE
YSlope = ZERO
CSlope = ZERO
END IF
YVal& = Y1 * 128: CVal& = col1 * 128
IF X1 < ZERO THEN X1 = ZERO
IF X2 > SRX THEN X2 = SRX
FOR f = X1 TO X2
IF scan(f).Y1 = ZERO THEN
scan(f).Y1 = YVal& \ 128
scan(f).clr1 = CVal& \ 128
ELSE
scan(f).Y2 = YVal& \ 128
scan(f).clr2 = CVal& \ 128
END IF
YVal& = YVal& + YSlope
CVal& = CVal& + CSlope
NEXT f
NEXT j
FOR f = xmin TO xmax
IF scan(f).Y1 > scan(f).Y2 THEN
Y1 = scan(f).Y2: Y2 = scan(f).Y1
col1 = scan(f).clr2: Col2 = scan(f).clr1
ELSE
Y1 = scan(f).Y1: Y2 = scan(f).Y2
col1 = scan(f).clr1: Col2 = scan(f).clr2
END IF
YDelta = Y2 - Y1: CDelta = Col2 - col1
IF YDelta = ZERO THEN YDelta = 1
CSlope = (CDelta / YDelta) * 128: CVal& = col1 * 128
FOR j = scan(f).Y1 TO scan(f).Y2
'clip polygon to screen (set boundaries)
IF f < SRX AND f > ZERO AND j > ZERO AND j < SRY THEN
pixel = CVal& \ 128: IF pixel > NumClr THEN pixel = NumClr
'write pixel to screen buffer
POKE aofs& + f + j * 320&, pixel
END IF
CVal& = CVal& + CSlope
NEXT j
NEXT f
END IF
NEXT i
PUT (ZERO, ZERO), ScnBuf(), PSET 'dump array to screen, like PCOPY
'******************************FRAME COUNTER****************************
'LOCATE 1, 1: PRINT fps: frame = frame + 1
'LOCATE 2, 1: PRINT TIMER - D#: D# = TIMER
'IF TIMER > t# THEN t# = TIMER + 1: fps = frame: frame = zero
LOOP
'------------------------------>END MAIN LOOP<--------------------------
ShutDown:
DEF SEG
SCREEN 0, 0, 0, 0: WIDTH 80, 25: CLS
PRINT "GS3DO.BAS by Matt Bross, 1997"
PRINT: PRINT "THERE WERE"; MaxPoints; "POINTS AND"; MaxPolys; "POLYGONS"
PRINT: PRINT "Free space"
PRINT " String Array Stack"
PRINT STRING$(21, "-")
'PRINT FRE(""); FRE(-1); FRE(-2): END
END
RETURN
ErrorHandler:
RESUME NEXT
'Puts a byte into the disk buffer... when the disk buffer is full it is
'dumped to disk.
SUB BufferWrite (a) STATIC
IF OAddress = OEndAddress THEN 'are we at the end of the buffer?
PUT GIFFile, , OutBuffer$ ' yup, write it out and
OAddress = OStartAddress ' start all over
END IF
POKE OAddress, a 'put byte in buffer
OAddress = OAddress + 1 'increment position
END SUB
'This routine gets one pixel from the display.
FUNCTION GetByte STATIC
GetByte = POINT(x, y) 'get the "byte"
x = x + 1 'increment X coordinate
IF x > MaxX THEN 'are we too far?
LINE (Minx, y)-(MaxX, y), 0 'a pacifier for impatient users
x = Minx 'go back to start
y = y + 1 'increment Y coordinate
IF y > MaxY THEN 'are we too far down?
Done = TRUE ' yup, flag it then
END IF
END IF
END FUNCTION
'
'-----------------------------------------------------------------------
' PDS 7.1 & QB4.5 GIF Compression Routine v1.00 By Rich Geldreich 1992
'-----------------------------------------------------------------------
'
'A$ = output filename
'ScreenX = X resolution of screen(320, 640, etc.)
'ScreenY = Y resolution of screen(200, 350, 480, etc.)
'XStart = <-upper left hand corner of area to encode
'YStart = < " "
'Xend = <-lower right hand corner of area to encode
'Yend = < " "
'NumColors = # of colors on screen(2, 16, 256)
'AdaptorType = 1 for EGA 2 for VGA
'NOTE: EGA palettes are not supported in this version of MakeGIF.
'
SUB MakeGif (a$, ScreenX, ScreenY, Xstart, YStart, Xend, Yend, NumColors, AdaptorType)
_TITLE "makegif"
'hash table's size - must be a prime number!
CONST Table.Size = 7177
DIM Prefix(Table.Size - 1), Suffix(Table.Size - 1), code(Table.Size - 1)
'The shift table contains the powers of 2 needed by the
'PutCode routine. This is done for speed. (much faster to
'look up an integer than to perform calculations...)
RESTORE ShiftTable
FOR a = 0 TO 7: READ Shift(a): NEXT
'MinX, MinY, MaxX, MaxY have the encoding window
Minx = Xstart: MinY = YStart
MaxX = Xend: MaxY = Yend
'Open GIF output file
GIFFile = FREEFILE 'use next free file
OPEN a$ FOR BINARY AS GIFFile
'Put GIF87a header at beginning of file
B$ = "GIF87a"
PUT GIFFile, , B$
'See how many colors are in this image...
SELECT CASE NumColors
CASE 2 'monochrome image
BitsPixel = 1 '1 bit per pixel
StartSize = 3 'first LZW code is 3 bits
StartCode = 4 'first free code
StartMax = 8 'maximum code in 3 bits
CASE 16 '16 colors images
BitsPixel = 4 '4 bits per pixel
StartSize = 5 'first LZW code is 5 bits
StartCode = 16 'first free code
StartMax = 32 'maximum code in 5 bits
CASE 256 '256 color images
BitsPixel = 8 '8 bits per pixel
StartSize = 9 'first LZW code is 9 bits
StartCode = 256 'first free code
StartMax = 512 'maximum code in 9 bits
END SELECT
'This following routine probably isn't needed- I've never
'had to use the "ColorBits" variable... With the EGA, you
'have 2 bits for Red, Green, & Blue. With VGA, you have 6 bits.
SELECT CASE AdaptorType
CASE 1
ColorBits = 2 'EGA
CASE 2
ColorBits = 6 'VGA
END SELECT
PUT GIFFile, , ScreenX 'put screen's dimensions
PUT GIFFile, , ScreenY
'pack colorbits and bits per pixel
a = 128 + (ColorBits - 1) * 16 + (BitsPixel - 1)
PUT GIFFile, , a
'throw a zero into the GIF file
a$ = CHR$(0)
PUT GIFFile, , a$
'Get the RGB palette from the screen and put it into the file...
SELECT CASE AdaptorType
CASE 1
STOP
'EGA palette routine not implemented yet
CASE 2
OUT &H3C7, 0
FOR a = 0 TO NumColors - 1
'Note: a BIOS call could be used here, but then we have to use
'the messy CALL INTERRUPT subs...
R = (INP(&H3C9) * 65280) \ 16128 'C=R * 4.0476190(for 0-255)
G = (INP(&H3C9) * 65280) \ 16128
B = (INP(&H3C9) * 65280) \ 16128
a$ = CHR$(R): PUT GIFFile, , a$
a$ = CHR$(G): PUT GIFFile, , a$
a$ = CHR$(B): PUT GIFFile, , a$
NEXT
END SELECT
'write out an image descriptor...
a$ = "," '"," is image seperator
PUT GIFFile, , a$ 'write it
PUT GIFFile, , Minx 'write out the image's location
PUT GIFFile, , MinY
ImageWidth = (MaxX - Minx + 1) 'find length & width of image
ImageHeight = (MaxY - MinY + 1)
PUT GIFFile, , ImageWidth 'store them into the file
PUT GIFFile, , ImageHeight
a$ = CHR$(BitsPixel - 1) '# bits per pixel in the image
PUT GIFFile, , a$
a$ = CHR$(StartSize - 1) 'store the LZW minimum code size
PUT GIFFile, , a$
'Initialize the vars needed by PutCode
CurrentBit = 0: Char& = 0
MaxCode = StartMax 'the current maximum code size
CodeSize = StartSize 'the current code size
ClearCode = StartCode 'ClearCode & EOF code are the
EOFCode = StartCode + 1 ' first two entries
StartCode = StartCode + 2 'first free code that can be used
NextCode = StartCode 'the current code
OutBuffer$ = STRING$(5000, 32) 'output buffer; for speedy disk writes
a& = SADD(OutBuffer$) 'find address of buffer
a& = a& - 65536 * (a& < 0)
Oseg = VARSEG(OutBuffer$) + (a& \ 16) 'get segment + offset >> 4
OAddress = a& AND 15 'get address into segment
OEndAddress = OAddress + 5000 'end of disk buffer
OStartAddress = OAddress 'current location in disk buffer
DEF SEG = Oseg
GOSUB ClearTree 'clear the tree & output a
PutCode ClearCode ' clear code
x = Xstart: y = YStart 'X & Y have the current pixel
Prefix = GetByte 'the first pixel is a special case
Done = FALSE 'True when image is complete
DO 'while there are more pixels to encode
DO 'until we have a new string to put into the table
IF Done THEN 'write out the last pixel, clear the disk buffer
'and fix up the last block so its count is correct
PutCode Prefix 'write last pixel
PutCode EOFCode 'send EOF code
IF CurrentBit <> 0 THEN
PutCode 0 'flush out the last code...
END IF
PutByte 0
OutBuffer$ = LEFT$(OutBuffer$, OAddress - OStartAddress)
PUT GIFFile, , OutBuffer$
a$ = ";" + STRING$(8, &H1A) 'the 8 EOF chars is not standard,
'but many GIF's have them, so how
'much could it hurt?
PUT GIFFile, , a$
a$ = CHR$(255 - BlockLength) 'correct the last block's count
PUT GIFFile, LastLoc&, a$
CLOSE GIFFile
EXIT SUB
ELSE 'get a pixel from the screen and see if we can find
'the new string in the table
Suffix = GetByte
GOSUB Hash 'is it there?
IF Found = TRUE THEN Prefix = code(index) 'yup, replace the
'prefix:suffix string with whatever
'code represents it in the table
END IF
LOOP WHILE Found 'don't stop unless we find a new string
PutCode Prefix 'output the prefix to the file
Prefix(index) = Prefix 'put the new string in the table
Suffix(index) = Suffix
code(index) = NextCode 'we've got to keep track if what code this is!
Prefix = Suffix 'Prefix=the last pixel pulled from the screen
NextCode = NextCode + 1 'get ready for the next code
IF NextCode = MaxCode + 1 THEN 'can an output code ever exceed
'the current code size?
'yup, increase the code size
MaxCode = MaxCode * 2
'Note: The GIF89a spec mentions something about a deferred clear
'code. When the clear code is deferred, codes are not entered
'into the hash table anymore. When the compression of the image
'starts to fall below a certain threshold, the clear code is
'sent and the hash table is cleared. The overall result is
'greater compression, because the table is cleared less often.
'This version of MakeGIF doesn't support this, because some GIF
'decoders crash when they attempt to enter too many codes
'into the string table.
IF CodeSize = 12 THEN 'is the code size too big?
PutCode ClearCode 'yup; clear the table and
GOSUB ClearTree 'start over
NextCode = StartCode
CodeSize = StartSize
MaxCode = StartMax
ELSE
CodeSize = CodeSize + 1 'just increase the code size if
END IF 'it's not too high( not > 12)
END IF
LOOP 'while we have more pixels
ClearTree:
FOR a = 0 TO Table.Size - 1 'clears the hashing table
Prefix(a) = -1 '-1 = invalid entry
Suffix(a) = -1
code(a) = -1
NEXT
RETURN
'this is only one of a plethora of ways to search the table for
'a match! I used a binary tree first, but I switched to hashing
'cause it's quicker(perhaps the way I implemented the tree wasn't
'optimal... who knows!)
Hash:
'hash the prefix & suffix(there are also many ways to do this...)
'?? is there a better formula?
index = ((Prefix * 256&) XOR Suffix) MOD Table.Size
'
'(Note: the table size(7177 in this case) must be a prime number, or
'else there's a chance that the routine will hang up... hate when
'that happens!)
'
'Calculate an offset just in case we don't find what we want on the
'first try...
IF index = 0 THEN 'can't have Table.Size-0 !
Offset = 1
ELSE
Offset = Table.Size - index
END IF
DO 'until we (1) find an empty entry or (2) find what we're lookin for
IF code(index) = -1 THEN 'is this entry blank?
Found = FALSE 'yup- we didn't find the string
RETURN
'is this entry the one we're looking for?
ELSEIF Prefix(index) = Prefix AND Suffix(index) = Suffix THEN
'yup, congrats you now understand hashing!!!
Found = TRUE
RETURN
ELSE
'shoot! we didn't find anything interesting, so we must
'retry- this is what slows hashing down. I could of used
'a bigger table, that would of speeded things up a little
'because this retrying would not happen as often...
index = index - Offset
IF index < 0 THEN 'too far down the table?
'wrap back the index to the end of the table
index = index + Table.Size
END IF
END IF
LOOP
END SUB
SUB pal (c, R, G, B)
OUT &H3C8, c
OUT &H3C9, R
OUT &H3C9, G
OUT &H3C9, B
END SUB
'Puts a byte into the GIF file & also takes care of each block.
SUB PutByte (a) STATIC
BlockLength = BlockLength - 1 'are we at the end of a block?
IF BlockLength <= 0 THEN ' yup,
BlockLength = 255 'block length is now 255
LastLoc& = LOC(1) + 1 + (OAddress - OStartAddress) 'remember the pos.
BufferWrite 255 'for later fixing
END IF
BufferWrite a 'put a byte into the buffer
END SUB
'Puts an LZW variable-bit code into the output file...
SUB PutCode (a) STATIC
Char& = Char& + a * Shift(CurrentBit) 'put the char were it belongs;
CurrentBit = CurrentBit + CodeSize ' shifting it to its proper place
DO WHILE CurrentBit > 7 'do we have a least one full byte?
PutByte Char& AND 255 ' yup! mask it off and write it out
Char& = Char& \ 256 'shift the bit buffer right 8 bits
CurrentBit = CurrentBit - 8 'now we have 8 less bits
LOOP 'until we don't have a full byte
END SUB
DECLARE SUB gifload (A$)
SUB gifload (filein$, wide%, high%)
DEFINT A-Z
CONST GifIdStr$ = "GIF87a"
CONST BitsInByte% = 8
CONST GifMaxEncodeBits% = 12
CONST GifBitsMag% = 4095 '* 2^GifMaxEncodeBits%-1 (aka 12 bits) CONST does not handle operations by another prior defined CONST :(
GifInChannel% = FREEFILE
IF GifInChannel% > 0 THEN
DIM Prefix(0 TO GifBitsMag%)
DIM Suffix(0 TO GifBitsMag%)
DIM OutStack(0 TO GifBitsMag%)
DIM shiftout%(8)
DIM Ybase AS LONG, powersof2(0 TO GifMaxEncodeBits% - 1) AS LONG, WorkCode AS LONG
FOR A% = 0 TO BitsInByte% - 1
shiftout%(BitsInByte% - A%) = 2 ^ A%
NEXT A%
FOR A% = 0 TO GifMaxEncodeBits% - 1
powersof2(A%) = 2 ^ A%
NEXT A%
IF filein$ = "" THEN
INPUT "GIF file"; filein$
IF filein$ = "" THEN END
END IF
IF INSTR(filein$, ".") = 0 THEN filein$ = filein$ + ".gif"
OPEN filein$ FOR BINARY AS #GifInChannel%
A$ = SPACE$(LEN(GifIdStr$))
GET #GifInChannel%, , A$
IF A$ <> GifIdStr$ THEN
PRINT "Not a "; GifIdStr$; " file."
EXIT SUB
END IF
GET #GifInChannel%, , TotalX: GET #GifInChannel%, , TotalY
GOSUB GetByte
NumColors = 2 ^ ((A% AND 7) + 1)
NoPalette = (A% AND 128) = 0
GOSUB GetByte
Background = A%
GOSUB GetByte
IF A% <> 0 THEN
PRINT "Bad screen descriptor."
EXIT SUB
END IF
IF NoPalette = 0 THEN
P$ = SPACE$(NumColors * 3)
GET #GifInChannel%, , P$
END IF
DO
GOSUB GetByte
IF A% = 44 THEN
EXIT DO
ELSEIF A% <> 33 THEN
PRINT "Unknown extension type.": END
END IF
GOSUB GetByte
DO
GOSUB GetByte
A$ = SPACE$(A%)
GET #GifInChannel%, , A$
LOOP UNTIL A% = 0
LOOP
GET #GifInChannel%, , XStart
GET #GifInChannel%, , YStart
GET #GifInChannel%, , XLength
GET #GifInChannel%, , YLength
XEnd = XStart + XLength
YEnd = YStart + YLength
GOSUB GetByte
IF A% AND 128 THEN PRINT "Can't handle local colormaps.": END
Interlaced = A% AND 64
PassNumber = 0
PassStep = 8
GOSUB GetByte
ClearCode = 2 ^ A%
EOSCode = ClearCode + 1
FirstCode = ClearCode + 2
NextCode = FirstCode
StartCodeSize = A% + 1
CodeSize = StartCodeSize
StartMaxCode = 2 ^ (A% + 1) - 1
MaxCode = StartMaxCode
BitsIn = 0
BlockSize = 0
BlockPointer = 1
x% = XStart
y% = YStart
Ybase = y% * wide%
SCREEN 13: DEF SEG = &HA000
IF NoPalette = 0 THEN
OUT &H3C7, 0
OUT &H3C8, 0
FOR A% = 1 TO NumColors * 3
OUT &H3C9, ASC(MID$(P$, A%, 1)) \ 4
NEXT A%
END IF
LINE (0, 0)-(wide% - 1, high% - 1), Background, BF
DO
GOSUB GetCode
IF Code <> EOSCode THEN
IF Code = ClearCode THEN
NextCode = FirstCode
CodeSize = StartCodeSize
MaxCode = StartMaxCode
GOSUB GetCode
CurCode = Code
LastCode = Code
LastPixel = Code
IF x% < wide% THEN POKE x% + Ybase, LastPixel
x% = x% + 1
IF x% = XEnd THEN GOSUB NextScanLine
ELSE
CurCode = Code
StackPointer = 0
IF Code > NextCode THEN EXIT DO
IF Code = NextCode THEN
CurCode = LastCode
OutStack(StackPointer) = LastPixel
StackPointer = StackPointer + 1
END IF
DO WHILE CurCode >= FirstCode
OutStack(StackPointer) = Suffix(CurCode)
StackPointer = StackPointer + 1
CurCode = Prefix(CurCode)
LOOP
LastPixel = CurCode
IF x% < wide% THEN POKE x% + Ybase, LastPixel
x% = x% + 1
IF x% = XEnd THEN GOSUB NextScanLine
FOR A% = StackPointer - 1 TO 0 STEP -1
IF x% < wide% THEN POKE x% + Ybase, OutStack(A%)
x% = x% + 1
IF x% = XEnd THEN GOSUB NextScanLine
NEXT A%
IF NextCode <= GifBitsMag% THEN
Prefix(NextCode) = LastCode
Suffix(NextCode) = LastPixel
NextCode = NextCode + 1
IF NextCode > MaxCode AND CodeSize < GifMaxEncodeBits% THEN
CodeSize = CodeSize + 1
MaxCode = MaxCode * 2 + 1
END IF
END IF
LastCode = Code
END IF
END IF
LOOP UNTIL DoneFlag OR Code = EOSCode
CLOSE #GifInChannel%
ERASE Prefix
ERASE Suffix
ERASE OutStack
ERASE shiftout%
ERASE powersof2
END IF
EXIT SUB
GetByte:
A$ = " "
GET #GifInChannel%, , A$
A% = ASC(A$)
RETURN
NextScanLine:
IF Interlaced THEN
y% = y% + PassStep
IF y% >= YEnd THEN
PassNumber = PassNumber + 1
SELECT CASE PassNumber
CASE 1
y% = 4
PassStep = 8
CASE 2
y% = 2
PassStep = 4
CASE 3
y% = 1
PassStep = 2
END SELECT
END IF
ELSE
y% = y% + 1
END IF
x% = XStart
Ybase = y% * wide%
DoneFlag = y% > high%
RETURN
GetCode:
IF BitsIn = 0 THEN
GOSUB ReadBufferedByte
LastChar = A%
BitsIn = 8
END IF
WorkCode = LastChar \ shiftout%(BitsIn)
DO WHILE CodeSize > BitsIn
GOSUB ReadBufferedByte
LastChar = A%
WorkCode = WorkCode OR LastChar * powersof2(BitsIn)
BitsIn = BitsIn + 8
LOOP
BitsIn = BitsIn - CodeSize
Code = WorkCode AND MaxCode
RETURN
ReadBufferedByte:
IF BlockPointer > BlockSize THEN
GOSUB GetByte: BlockSize = A%
A$ = SPACE$(BlockSize)
GET #GifInChannel%, , A$
BlockPointer = 1
END IF
A% = ASC(MID$(A$, BlockPointer, 1))
BlockPointer = BlockPointer + 1
RETURN
END SUB
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