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StarInfo/Wood/Smudge/!Help
This website contains an archive of files for the Acorn Electron, BBC Micro, Acorn Archimedes, Commodore 16 and Commodore 64 computers, which Dominic Ford has rescued from his private collection of floppy disks and cassettes.
Some of these files were originally commercial releases in the 1980s and 1990s, but they are now widely available online. I assume that copyright over them is no longer being asserted. If you own the copyright and would like files to be removed, please contact me.
| Tape/disk: | Home » Recent acquisitions » Acorn ADFS disks » adfs_AcornUser_199610.adf » Regulars |
| Filename: | StarInfo/Wood/Smudge/!Help |
| Read OK: | ✔ |
| File size: | 0605 bytes |
| Load address: | 0000 |
| Exec address: | 0000 |
File contents
!Help
!Smudge was written by Keith Wood. It demonstrates the use of full screen pixel softening in a 16 colour mode. This program should work in any 16 colour mode.
Controls
--------
Mouse controls position of brush
Mouse buttons: Left - Paint with brush
Middle - Change brush
Right - Pause
About this program
------------------
The idea behind pixel softening in a 16 colour mode is that, unlike 256 colour mode, there are no RGB components to separate. Instead the colours are set up so that white is colour 15 and black is 0, and all the colours in-between follow a uniform grey scale. Softening is then a simple matter of taking a weighted average of a 3x3 grid of pixels and storing the result in the middle pixel.
The pixels are weighted are as follows:
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| 1 | 2 | 1 |
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| 2 | 4 | 2 |
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| 1 | 2 | 1 |
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To get this weighting, a horizontal softening routine is applied to the screen, and written back to memory, before applying a vertical routine.
The real problem is realising that a word of eight pixels is stored back to front with interleaving?!! So some approximations were made to ignore the interleaving, and use the fact that many pixels can be operated on simultaneously to speed up the code - not as simple as it sounds. However, most computers will not exhibit any lasting side effects after executing the code, and neither will the code exhibit any lasting side effects after executing the computer.
00000000 21 48 65 6c 70 0a 0a 21 53 6d 75 64 67 65 20 77 |!Help..!Smudge w| 00000010 61 73 20 77 72 69 74 74 65 6e 20 62 79 20 4b 65 |as written by Ke| 00000020 69 74 68 20 57 6f 6f 64 2e 20 49 74 20 64 65 6d |ith Wood. It dem| 00000030 6f 6e 73 74 72 61 74 65 73 20 74 68 65 20 75 73 |onstrates the us| 00000040 65 20 6f 66 20 66 75 6c 6c 20 73 63 72 65 65 6e |e of full screen| 00000050 20 70 69 78 65 6c 20 73 6f 66 74 65 6e 69 6e 67 | pixel softening| 00000060 20 69 6e 20 61 20 31 36 20 63 6f 6c 6f 75 72 20 | in a 16 colour | 00000070 6d 6f 64 65 2e 20 54 68 69 73 20 70 72 6f 67 72 |mode. This progr| 00000080 61 6d 20 73 68 6f 75 6c 64 20 77 6f 72 6b 20 69 |am should work i| 00000090 6e 20 61 6e 79 20 31 36 20 63 6f 6c 6f 75 72 20 |n any 16 colour | 000000a0 6d 6f 64 65 2e 0a 0a 20 20 20 20 43 6f 6e 74 72 |mode... Contr| 000000b0 6f 6c 73 0a 20 20 20 20 2d 2d 2d 2d 2d 2d 2d 2d |ols. --------| 000000c0 0a 0a 20 4d 6f 75 73 65 20 63 6f 6e 74 72 6f 6c |.. Mouse control| 000000d0 73 20 70 6f 73 69 74 69 6f 6e 20 6f 66 20 62 72 |s position of br| 000000e0 75 73 68 0a 0a 20 4d 6f 75 73 65 20 62 75 74 74 |ush.. Mouse butt| 000000f0 6f 6e 73 3a 20 4c 65 66 74 20 20 20 2d 20 50 61 |ons: Left - Pa| 00000100 69 6e 74 20 77 69 74 68 20 62 72 75 73 68 0a 20 |int with brush. | 00000110 20 20 20 20 20 20 20 20 20 20 20 20 20 20 20 4d | M| 00000120 69 64 64 6c 65 20 2d 20 43 68 61 6e 67 65 20 62 |iddle - Change b| 00000130 72 75 73 68 0a 20 20 20 20 20 20 20 20 20 20 20 |rush. | 00000140 20 20 20 20 20 52 69 67 68 74 20 20 2d 20 50 61 | Right - Pa| 00000150 75 73 65 0a 0a 0a 20 20 20 20 41 62 6f 75 74 20 |use... About | 00000160 74 68 69 73 20 70 72 6f 67 72 61 6d 0a 20 20 20 |this program. | 00000170 20 2d 2d 2d 2d 2d 2d 2d 2d 2d 2d 2d 2d 2d 2d 2d | ---------------| 00000180 2d 2d 2d 0a 0a 20 54 68 65 20 69 64 65 61 20 62 |---.. The idea b| 00000190 65 68 69 6e 64 20 70 69 78 65 6c 20 73 6f 66 74 |ehind pixel soft| 000001a0 65 6e 69 6e 67 20 69 6e 20 61 20 31 36 20 63 6f |ening in a 16 co| 000001b0 6c 6f 75 72 20 6d 6f 64 65 20 69 73 20 74 68 61 |lour mode is tha| 000001c0 74 2c 20 75 6e 6c 69 6b 65 20 32 35 36 20 63 6f |t, unlike 256 co| 000001d0 6c 6f 75 72 20 6d 6f 64 65 2c 20 74 68 65 72 65 |lour mode, there| 000001e0 20 61 72 65 20 6e 6f 20 52 47 42 20 63 6f 6d 70 | are no RGB comp| 000001f0 6f 6e 65 6e 74 73 20 74 6f 20 73 65 70 61 72 61 |onents to separa| 00000200 74 65 2e 20 49 6e 73 74 65 61 64 20 74 68 65 20 |te. Instead the | 00000210 63 6f 6c 6f 75 72 73 20 61 72 65 20 73 65 74 20 |colours are set | 00000220 75 70 20 73 6f 20 74 68 61 74 20 77 68 69 74 65 |up so that white| 00000230 20 69 73 20 63 6f 6c 6f 75 72 20 31 35 20 61 6e | is colour 15 an| 00000240 64 20 62 6c 61 63 6b 20 69 73 20 30 2c 20 61 6e |d black is 0, an| 00000250 64 20 61 6c 6c 20 74 68 65 20 63 6f 6c 6f 75 72 |d all the colour| 00000260 73 20 69 6e 2d 62 65 74 77 65 65 6e 20 66 6f 6c |s in-between fol| 00000270 6c 6f 77 20 61 20 75 6e 69 66 6f 72 6d 20 67 72 |low a uniform gr| 00000280 65 79 20 73 63 61 6c 65 2e 20 53 6f 66 74 65 6e |ey scale. Soften| 00000290 69 6e 67 20 69 73 20 74 68 65 6e 20 61 20 73 69 |ing is then a si| 000002a0 6d 70 6c 65 20 6d 61 74 74 65 72 20 6f 66 20 74 |mple matter of t| 000002b0 61 6b 69 6e 67 20 61 20 77 65 69 67 68 74 65 64 |aking a weighted| 000002c0 20 61 76 65 72 61 67 65 20 6f 66 20 61 20 33 78 | average of a 3x| 000002d0 33 20 67 72 69 64 20 6f 66 20 70 69 78 65 6c 73 |3 grid of pixels| 000002e0 20 61 6e 64 20 73 74 6f 72 69 6e 67 20 74 68 65 | and storing the| 000002f0 20 72 65 73 75 6c 74 20 69 6e 20 74 68 65 20 6d | result in the m| 00000300 69 64 64 6c 65 20 70 69 78 65 6c 2e 0a 20 54 68 |iddle pixel.. Th| 00000310 65 20 70 69 78 65 6c 73 20 61 72 65 20 77 65 69 |e pixels are wei| 00000320 67 68 74 65 64 20 61 72 65 20 61 73 20 66 6f 6c |ghted are as fol| 00000330 6c 6f 77 73 3a 0a 0a 20 2d 2d 2d 2d 2d 2d 2d 2d |lows:.. --------| 00000340 2d 2d 2d 2d 2d 0a 20 7c 20 31 20 7c 20 32 20 7c |-----. | 1 | 2 || 00000350 20 31 20 7c 0a 20 2d 2d 2d 2d 2d 2d 2d 2d 2d 2d | 1 |. ----------| 00000360 2d 2d 2d 0a 20 7c 20 32 20 7c 20 34 20 7c 20 32 |---. | 2 | 4 | 2| 00000370 20 7c 0a 20 2d 2d 2d 2d 2d 2d 2d 2d 2d 2d 2d 2d | |. ------------| 00000380 2d 0a 20 7c 20 31 20 7c 20 32 20 7c 20 31 20 7c |-. | 1 | 2 | 1 || 00000390 0a 20 2d 2d 2d 2d 2d 2d 2d 2d 2d 2d 2d 2d 2d 0a |. -------------.| 000003a0 0a 20 54 6f 20 67 65 74 20 74 68 69 73 20 77 65 |. To get this we| 000003b0 69 67 68 74 69 6e 67 2c 20 61 20 68 6f 72 69 7a |ighting, a horiz| 000003c0 6f 6e 74 61 6c 20 73 6f 66 74 65 6e 69 6e 67 20 |ontal softening | 000003d0 72 6f 75 74 69 6e 65 20 69 73 20 61 70 70 6c 69 |routine is appli| 000003e0 65 64 20 74 6f 20 74 68 65 20 73 63 72 65 65 6e |ed to the screen| 000003f0 2c 20 61 6e 64 20 77 72 69 74 74 65 6e 20 62 61 |, and written ba| 00000400 63 6b 20 74 6f 20 6d 65 6d 6f 72 79 2c 20 62 65 |ck to memory, be| 00000410 66 6f 72 65 20 61 70 70 6c 79 69 6e 67 20 61 20 |fore applying a | 00000420 76 65 72 74 69 63 61 6c 20 72 6f 75 74 69 6e 65 |vertical routine| 00000430 2e 0a 20 0a 20 54 68 65 20 72 65 61 6c 20 70 72 |.. . The real pr| 00000440 6f 62 6c 65 6d 20 69 73 20 72 65 61 6c 69 73 69 |oblem is realisi| 00000450 6e 67 20 74 68 61 74 20 61 20 77 6f 72 64 20 6f |ng that a word o| 00000460 66 20 65 69 67 68 74 20 70 69 78 65 6c 73 20 69 |f eight pixels i| 00000470 73 20 73 74 6f 72 65 64 20 62 61 63 6b 20 74 6f |s stored back to| 00000480 20 66 72 6f 6e 74 20 77 69 74 68 20 69 6e 74 65 | front with inte| 00000490 72 6c 65 61 76 69 6e 67 3f 21 21 20 53 6f 20 73 |rleaving?!! So s| 000004a0 6f 6d 65 20 61 70 70 72 6f 78 69 6d 61 74 69 6f |ome approximatio| 000004b0 6e 73 20 77 65 72 65 20 6d 61 64 65 20 74 6f 20 |ns were made to | 000004c0 69 67 6e 6f 72 65 20 74 68 65 20 69 6e 74 65 72 |ignore the inter| 000004d0 6c 65 61 76 69 6e 67 2c 20 61 6e 64 20 75 73 65 |leaving, and use| 000004e0 20 74 68 65 20 66 61 63 74 20 74 68 61 74 20 6d | the fact that m| 000004f0 61 6e 79 20 70 69 78 65 6c 73 20 63 61 6e 20 62 |any pixels can b| 00000500 65 20 6f 70 65 72 61 74 65 64 20 6f 6e 20 73 69 |e operated on si| 00000510 6d 75 6c 74 61 6e 65 6f 75 73 6c 79 20 74 6f 20 |multaneously to | 00000520 73 70 65 65 64 20 75 70 20 74 68 65 20 63 6f 64 |speed up the cod| 00000530 65 20 2d 20 6e 6f 74 20 61 73 20 73 69 6d 70 6c |e - not as simpl| 00000540 65 20 61 73 20 69 74 20 73 6f 75 6e 64 73 2e 20 |e as it sounds. | 00000550 48 6f 77 65 76 65 72 2c 20 6d 6f 73 74 20 63 6f |However, most co| 00000560 6d 70 75 74 65 72 73 20 77 69 6c 6c 20 6e 6f 74 |mputers will not| 00000570 20 65 78 68 69 62 69 74 20 61 6e 79 20 6c 61 73 | exhibit any las| 00000580 74 69 6e 67 20 73 69 64 65 20 65 66 66 65 63 74 |ting side effect| 00000590 73 20 61 66 74 65 72 20 65 78 65 63 75 74 69 6e |s after executin| 000005a0 67 20 74 68 65 20 63 6f 64 65 2c 20 61 6e 64 20 |g the code, and | 000005b0 6e 65 69 74 68 65 72 20 77 69 6c 6c 20 74 68 65 |neither will the| 000005c0 20 63 6f 64 65 20 65 78 68 69 62 69 74 20 61 6e | code exhibit an| 000005d0 79 20 6c 61 73 74 69 6e 67 20 73 69 64 65 20 65 |y lasting side e| 000005e0 66 66 65 63 74 73 20 61 66 74 65 72 20 65 78 65 |ffects after exe| 000005f0 63 75 74 69 6e 67 20 74 68 65 20 63 6f 6d 70 75 |cuting the compu| 00000600 74 65 72 2e 0a |ter..| 00000605
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