98 lines
3.3 KiB
Plaintext
98 lines
3.3 KiB
Plaintext
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{-----------------------------------------------------------------------+
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| Screen test |
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+-----------------------------------------------------------------------}
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gcl0x
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{
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This is the original Easter Egg "hidden" in ROM v1.
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So the names are obscured, and originally this file was uncommented.
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The image data is a stream of packed 6-bit pixels from ROM.
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The pixel data is XORed with all-ones (63).
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The value after a raw zero is a repeat count for 1..63 white pixels.
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If the repeat count is 0, we are at the end of the image.
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}
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$0101 ShiftControl=
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[def
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{ Select random screen memory position `q': }
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{ X ranges from 0..255 and Y from 8..127 }
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[do
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\SYS_Random_34 _sysFn= 34!! q=
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q>, 120- if>=0loop]
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128+ q>.
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q r= 72+ r<. {End of line `r', 72 pixels wide image}
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0 i= {Index in unpacked byte buffer}
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n= {Count, or -1 when reading new count}
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{ Loop until end of image stream }
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[do
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{ Fill buffer with next group of 4 bytes when needed }
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n [if<=0
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i [if=0 {Reached end of unpack buffer}
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p 0?? \sysArgs0. {Packed byte 0}
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p 1?? \sysArgs1. {Packed byte 1}
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p 2?? \sysArgs2. {Packed byte 2}
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p 3+ p= 255& {Advance read pointer}
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249^ [if=0 p 7+ p=] {Skip trampolines}
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\SYS_Unpack_56 _sysFn=
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56!! {Unpack 3 to 4 bytes}
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]
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n
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]
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[if<0 {n == -1}
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{ Read repeat count for white pixels }
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\sysArgs0 i+ peek n=
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[if=0 ret] {End of image}
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i 1+ 3& i= {Rotate through 4-byte unpack buffer}
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else
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[if>0 {n > 0}
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{ Force white pixel }
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63 q.
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n 1- n=
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q<++ {Update X, but don't update i}
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else {n == 0, normal operation}
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{ Consume next pixel from stream }
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\sysArgs0 i+ peek [if<>0
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63^ q. {New pixel, not white}
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q<++
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else
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-1 n= {Next value is a repeat count}
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]
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i 1+ 3& i= {Rotate through 4-byte unpack buffer}
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]
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]
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{ Wrap write pointer }
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q r- [if=0
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0 q. {1 pixel border/shadow on the right side}
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q 72- q<. q>++ {Next line}
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q [if<0 $8800 q+ q=] {Wrap around bottom of screen memory}
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q>, r>.
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]
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\frameCount, ShiftControl. {Smooth scrolling}
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loop]
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] Transfer=
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{--- Run ---}
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[do
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\gigatronRaw p= {Pointer to packed image data}
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{ Contains the packed image data for}
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{ Marcel's and Walter's portraits}
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Transfer! {Unpack and draw first image}
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Transfer! {Unpack and draw second image}
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loop] {Repeat forever}
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{-----------------------------------------------------------------------+
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| End |
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+-----------------------------------------------------------------------}
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