LIST 2 7.TXT
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**********************************************************************
* *
* 68000 ASSEMBLER COURSE ON ATARI ST *
* *
* by The Fierce Rabbit (from 44E) *
* *
* Listing number 2 / Course number 7 *
* *
**********************************************************************
* Test resolution, because if we are in high and we try to *
* switch to low, bam! RESET! *
MOVE.W #4,-(SP) Getrez() function number
TRAP #14 Xbios call
ADDQ.L #2,SP stack correction
CMP.W #2,D0 high resolution?
BEQ LOAD yes, so load everything now
* Since we are not in high resolution, we force into low resolution
* first we note by setting a flag to 1
MOVE.W #1,RESOLUTION
MOVE.W #0,-(SP) low resolution
MOVE.L #-1,-(SP) unchanged screen address
MOVE.L #-1,-(SP) unchanged screen address
MOVE.W #5,-(SP) Setscreen() function
TRAP #14 X bios
ADDA.L #12,SP correction
* Opening of the image file
LOAD MOVE.W #0,-(SP) opening in read mode
MOVE.L #FILENAME_ADDRESS,-(SP) addr of the file name
MOVE.W #61,-(SP) Fopen() function
TRAP #1 from GEMDOS
ADDQ.L #8,SP stack correction
* D0 contains the Handle or a negative error number
TST.W D0 compare to 0
BLT ERROR less than so error
* We save the file handle
MOVE.W D0,D3
* Skip the first 34 bytes of the DEGAS file
* (2 header bytes, 32 for colors)
MOVE.W #0,-(SP) shift from the start of
file
MOVE.W D3,-(SP) file handle
MOVE.L #34,-(SP) number of bytes to skip
MOVE.W #66,-(SP) Fseek() function
TRAP #1 from GEMDOS
ADDA.L #10,SP
TST.W D0 test D0
BLT ERROR
* Determine the screen address
MOVE.W #2,-(SP) Physbase() function
TRAP #14 xbios
ADDQ.L #2,SP stack correction
MOVE.L D0,A5 save address
* Load the image directly onto the screen
MOVE.L A5,-(SP) destination address
MOVE.L #32000,-(SP) number of bytes to read
MOVE.W D3,-(SP) file handle
MOVE.W #63,-(SP) Fread() function
TRAP #1 from GEMDOS
ADDA.L #12,SP
TST.W D0
BLT ERROR
* Load the palette into our palette buffer
* First reposition the file pointer
MOVE.W #0,-(SP) shift from the start of
file
MOVE.W D3,-(SP) file handle
MOVE.L #2,-(SP) number of bytes to skip
MOVE.W #66,-(SP) Fseek() function
TRAP #1 from GEMDOS
ADDA.L #10,SP
TST.W D0 test D0
BLT ERROR
* Then loading
MOVE.L #PALETTE_BUFFER,-(SP) destination address
MOVE.L #32,-(SP) number of bytes to read
MOVE.W D3,-(SP) file handle
MOVE.W #63,-(SP) Fread() function
TRAP #1 from GEMDOS
ADDA.L #12,SP
TST.W D0
BLT ERROR
* Now we set this palette with Xbios (6)
MOVE.L #PALETTE_BUFFER,-(SP) black palette address
MOVE.W #6,-(SP) SetPalette() function
TRAP #14 XBIOS
ADDQ.L #6,SP
* We close the file
MOVE.W D3,-(SP) handle
MOVE.W #62,-(SP) Fclose() function
TRAP #1 from GEMDOS
ADDQ.L #4,SP
BRA END and we get out
* In case of error we come here
ERROR MOVE.L #ERROR_MESSAGE,-(SP) informs
MOVE.W #9,-(SP)
TRAP #1
ADDQ.L #6,SP
END MOVE.W #7,-(SP) wait for a key press
TRAP #1
ADDQ.L #2,SP
CMP.W #0,RESOLUTION
BEQ NOT_MEDIUM
* Since we are in low, we force back into medium resolution
MOVE.W #1,-(SP) medium resolution
MOVE.L #-1,-(SP) unchanged screen address
MOVE.L #-1,-(SP) unchanged screen address
MOVE.W #5,-(SP) Setscreen() function
TRAP #14 XBIOS
ADDA.L #12,SP correction
* Then we exit
NOT_MEDIUM
MOVE.W #0,-(SP)
TRAP #1
*-------------------------------------------------------------*
SECTION DATA
ERROR_MESSAGE DC.B "Sorry, error with",13,10
DC.B "the file "
FILENAME_ADDRESS DC.B "A:\IMAGE.PI1",0
SECTION BSS
PALETTE_BUFFER DS.W 16
RESOLUTION DS.W 1
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