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- ; Original file at
- ; http://dailly.blogspot.it/2017/06/zx-spectrum-next-bitmap-example.html
- ; Disassembly of the file "bitmaps\BMPLOAD"
- ;
- ; BMP Port $123b
- ; bit 0 - Write enable. (banks in 16K from $0000-$3fff)
- ; bit 1 - bitmap ON
- ; bit 4 - Layer 2 below spectrum screen
- ; bit 6-7 - Which 16K bank to page into $0000-$3ffff
- ;
- ; On entry, HL = arguments
- ;
- ;
- ; Since dot commands run at $2000, and the Layer 2 is paged into $0000-$3fff
- ; It needs to have some code above the lower 16K to actually copy into layer 2
- ; So copy up the "copy" routine, and it'll page in/out the layer 2 bank
- ;
- 2000 226221 ld (HL_Save),hl ; Store HL
- 2003 216421 ld hl,UploadCode ; Src =
- 2006 110060 ld de,6000h ; dest = $6000
- 2009 011f00 ld bc,001fh ; size = 31 bytes
- 200c edb0 ldir
- 200e 2a6221 ld hl,(HL_Save) ; get HL back
- 2011 7c ld a,h
- 2012 b5 or l ; is hl 0?
- 2013 2008 jr nz,201dh ; if we have an argument, carry on
- 2015 213121 ld hl,2131h ; get message
- 2018 cd1d21 call PrintText ; print the filename
- 201b 1823 jr Exit ; exit
- ; Load file....?
- CopyFilename:
- 201d 112421 ld de,FileName ; "filename.ext" text - space to store filename?
- 2020 060c ld b,0ch ; b = $0c (max length of allowed filename - no path it seems)
- ; Copy, and validate characters in filename
- 2022 7e ld a,(hl) ; first byte of filename
- 2023 fe3a cp 3ah ; is it a ":"? End of filename
- 2025 2810 jr z,EndFilename ; if so end of filename
- 2027 b7 or a ; 0?
- 2028 280d jr z,EndFilename ; if so end of filename
- 202a fe0d cp 0dh ; newline?
- 202c 2809 jr z,EndFilename ; if so end of filename
- 202e cb7f bit 7,a ; over 127?
- 2030 2005 jr nz,EndFilename ; if so end of filename
- 2032 12 ld (de),a ; copy over to filename cache
- 2033 23 inc hl ; next src letter
- 2034 13 inc de ; next dest letter
- 2035 10eb djnz 2022h ; copy all
- EndFilename
- 2037 af xor a ; Mark end of filename
- 2038 12 ld (de),a ; store filename
- 2039 dd212421 ld ix,FileName ; get filename base address
- 203d cd6220 call LoadFile:
- Exit:
- 2040 af xor a ; no error
- 2041 c9 ret ; exit
- ; esxDOS detect if unit is ready
- DetectUnit:
- 2042 af xor a ; Detect if unit is ready
- 2043 cf rst 08h ; call esxDOS
- 2044 89 db $89 ; M_GETSETDRV
- ; Open
- ; IX= Filename (ASCIIZ)
- ; B = FA_READ ($01)
- ; FA_APPEND ($06)
- ; FA_OVERWRITE ($0C)
- ;
- OpenFile:
- 2045 dde5 push ix ; ix = filename
- 2047 e1 pop hl ; If a DOT command (rather than normal memory), uses HL not IX
- 2048 0601 ld b,01h ; b = FA_READ
- 204a 3e2a ld a,2ah ; a = unknown (a=0 for open)
- 204c cf rst 08h ; call esxDOS
- 204d 9a db $9a ; F_Open
- 204e 325620 ld (2056h),a ; Store file handle (self modify read from file code)
- 2051 c9 ret ;
- ; esxDOS command - Read from file - command $9d
- ; IX = address to load into
- ; BC = number of bytes to load
- ; A = file handle
- ReadBytes:
- 2052 dde5 push ix ; IX = where to to store data
- 2054 e1 pop hl ; get address to load into
- 2055 3e00 ld a,00h ; $00 is self modified
- 2057 cf rst 08h ; call esxDOS
- 2058 9d db $9d ; F_Read
- 2059 c9 ret
- ; esxDOS command - Close File - command $9b
- ; A = file handle
- CloseFile:
- 205a 3a5620 ld a,(2056h) ; Get open file handle
- 205d b7 or a ; is it 0? (did it open)
- 205e c8 ret z ; if file handle is 0, return
- 205f cf rst 08h ; Call esxDOS
- 2060 9b db $9b ; F_Close
- 2061 c9 ret
- LoadFile:
- 2062 dde5 push ix ; remember filename
- 2064 cd4220 call DetectUnit ; detect unit and open...?!?!?
- 2067 dde1 pop ix ; get filename back
- 2069 cd4520 call OpenFile ; OpenFile - again??
- 206c dd21e720 ld ix,BMPHeader ; Read the BMP file header
- 2070 013600 ld bc,0036h ; read header ($36 bytes)
- 2073 cd5220 call ReadBytes
- 2076 dd218321 ld ix,BitMap ; read block into $2183
- 207a 010004 ld bc,0400h ; read palette - 1024 bytes
- 207d cd5220 call ReadBytes
- ;
- ; Convert the 24bit palette into a simple RRRGGGBB format
- ;
- ConvertBMP:
- 2080 218321 ld hl,BitMap ; Get buffer address ($2183)
- 2083 11003f ld de,3f00h ; Dest address of converted palette
- 2086 0600 ld b,00h
- ConvertionLoop:
- 2088 7e ld a,(hl) ; get BLUE byte
- 2089 23 inc hl ; move on to green
- 208a c620 add a,20h ; brighten up a bit? (blue is always pretty dark??)
- 208c 3002 jr nc,SkipSatB ; overflow?
- 208e 3eff ld a,0ffh ; if overflow, then saturate to $FF
- SkipSatB:
- 2090 1f rra ; get top 2 bits only RRRGGGBB
- 2091 1f rra
- 2092 1f rra
- 2093 1f rra
- 2094 1f rra
- 2095 1f rra
- 2096 e603 and 03h ; and store them at the bottom
- 2098 4f ld c,a ; c holds current byte
- 2099 7e ld a,(hl) ; get GREEN
- 209a 23 inc hl ; move onto red
- 209b c610 add a,10h ; brighten up a bit as well
- 209d 3002 jr nc,SkipSatG ; if no overflow, skip saturate
- 209f 3eff ld a,0ffh
- SkipSatG:
- 20a1 1f rra ; get 3 bits of green into right place
- 20a2 1f rra
- 20a3 1f rra
- 20a4 e61c and 1ch ; mask off remaining lower bits
- 20a6 b1 or c ; merge with output byte
- 20a7 4f ld c,a ; store into output
- 20a8 7e ld a,(hl) ; get RED
- 20a9 23 inc hl ; move to next byte of colour (assuming alpha)
- 20aa c610 add a,10h ; brighten up a bit
- 20ac 3002 jr nc,SkipSatR ; no overflow?
- 20ae 3eff ld a,0ffh ; Saturate to $FF
- SkipSatR
- 20b0 e6e0 and 0e0h ; keep top 3 bits
- 20b2 b1 or c ; merge with output pixel
- 20b3 12 ld (de),a ; store converted pixel
- 20b4 13 inc de ; move to next ouput pixel
- 20b5 23 inc hl ; move to next BGRA pixel
- 20b6 10d0 djnz ConvertionLoop ; c = pixel....?!?!?!
- 20b8 06c0 ld b,0c0h ; bc=$c000
- ConvertUploadLoop:
- 20ba c5 push bc
- 20bb dd21003e ld ix,3e00h ; $3e00 = Destination address
- 20bf 010001 ld bc,0100h ; read 256 bytes of data
- 20c2 cd5220 call ReadBytes ; Read from file
- ;
- ; convert 256 value palette index into actual RGB byte pixel using palette lookup
- ;
- 20c5 2e00 ld l,00h ; l = xx (loop counter)
- CopyLoop:
- 20c7 263e ld h,3eh ; hl = $3exx
- 20c9 5e ld e,(hl) ; e = Get palette index
- 20ca 163f ld d,3fh ; d = $3f palette base address - 256 byte aligned
- 20cc 1a ld a,(de) ; a = palette value (24bit converted downto 8bit)
- 20cd 265b ld h,5bh ; hl = $5bxx converted 256 byte buffer
- 20cf 77 ld (hl),a ; ($5bxx) = converted colour pixel
- 20d0 263e ld h,3eh ; hl = $3e00
- 20d2 2c inc l ; do 256 bytes of this....
- 20d3 20f2 jr nz,CopyLoop
- 20d5 c1 pop bc ; bc = $c000
- 20d6 c5 push bc
- 20d7 cd0060 call 6000h ; block transfer 256 bytes of the bitmap
- 20da c1 pop bc
- 20db 10dd djnz ConvertUploadLoop
- 20dd 013b12 ld bc,123bh ; Bitmap port
- 20e0 3e02 ld a,02h ; 2 = enable and visible
- 20e2 ed79 out (c),a ; switch bitmap layer 2 on
- 20e4 c35a20 jp 205ah
- BMPHeader: ds 54 ; $20e7 to $211c
- PrintText:
- 211d 7e ld a,(hl) ; get character
- 211e 23 inc hl ; move to next one
- 211f b7 or a ; is this 0?
- 2120 c8 ret z ; if so... end of string
- 2121 d7 rst 10h ; outchr()
- 2122 18f9 jr 211dh ; print all characters
- ;
- ; Looks like data of some kinds
- ;
- FileName: db "filename.ext",0
- Message: db ".picload to load image to background",$d,$00
- HL_Save dw 0
- ;
- ; Copied up to $6000
- ;
- UploadCode:
- 2164 05 dec b ; b = upper byte of memory address
- 2165 78 ld a,b ; get 256 byte page into a
- 2166 e63f and 3fh ; ignore top bits
- 2168 57 ld d,a ; de=$0000-$3ffff
- 2169 1e00 ld e,00h ; Page bitmap block into lower 16K
- 216b 78 ld a,b
- 216c e6c0 and 0c0h ; get the 16K bank to page
- 216e f601 or 01h ; OR in bank active bit
- 2170 013b12 ld bc,123bh ; bitmap register
- 2173 ed79 out (c),a ; map bank into memory perhaps?
- 2175 21005b ld hl,5b00h ; $5b00 src image chunk
- 2178 010001 ld bc,0100h ; 256 byte copy (one line)
- 217b edb0 ldir ; copy up (de=dest)
- 217d 013b12 ld bc,123bh ; bitmap register
- 2180 ed69 out (c),l ; l=0, disable current bank and screen
- 2182 c9 ret
- BitMap:
- 2183 00 nop ; file is loaded into here....
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