Home » Personal collection » Acorn ADFS disks » Archimedes » Unlabelled_disk_2.ADF » PT/+P3

PT/+P3

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 » Personal collection » Acorn ADFS disks » Archimedes » Unlabelled_disk_2.ADF
Filename: PT/+P3
Read OK: ✔
File size: 0BD3 bytes
Load address: D4556
Exec address: 8FF8
Duplicates

There are 5 duplicate copies of this file in the archive:

File contents
     This is where MOVE, DRAW and PLOT are useful. Using these commands,
lines can be drawn across the screen, and, using PLOT, triangles can be
drawn. These commands are covered in the Graphics chapter of the user
manual. The other major advantage of these graphics commands is that they
can be used not just to set the colour of an area, but also to invert it.
The GCOL command, which selects the colour in which graphics are
displayed, takes two parameters:

GCOL x,c

c is the new colour in which graphics should be drawn.
x selects how this colour should be applyed:

x=0 means to set every pixel to that colour, regardless of its 
previous colour.
x=1 means to mix the light from the pixel already on the screen 
with that of the new colour. For example, if a red pixel is set 
to blue, the red and blue mix to form purple.
x=2 means that the light from the pixels is filtered with the new 
colour. If a red pixel is set to blue now, it is as if a blue 
filter has been placed in front of the red light, and the 
resultant colour is black (red light contains no blue component).
x=3 means to invert the old colour with the new colour.
x=4 means to set the pixels with the inverse of the new colour 
(regardless of the old colour).

     Lines may now be drawn across the screen by typing:

MOVE x,y:DRAW xb,yb

Where: (x,y)   = The co-ordinate of the first point on the line.
       (xb,yb) = That of the last point on the line.

     The range of the screen is always 1280 pixels across, and 1024 pixels 
down. The bottom left corner is point (0,0), and the top right corner is 
(1280,1024). Larger graphics can be drawn using the PLOT command. The most 
common usage is as follows:

MOVE x,y: MOVE xb,yb:PLOT 85,xc,yc

     This plots a filled triangle with corners at (x,y), (xb,yb) and 
(xc,yc). PLOT also has many other functions - see the User Guide for details.
     At first sight, it may seem that user defined characters serve no
purpose once a programmer has learnt about the more flexible graphics
commands, but this is not the case. If you try to produce detailed
graphics using MOVE and DRAW, you will find that your program crawls
along at an unacceptable rate. User defined characters, on the other
hand, can produce detail quickly, especially if the pattern repeats, so
that one character definition can be used repeatedly in several areas of
the screen. This is demonstrated by the program which is available at the
end of the tutorial.
     So, it seems that programmers are faced with a difficult problem.
They can use graphics commands and get colour, or they can use user
defined characters and get detail, but what if they want both at the same
time? There must be a solution - how else would games like Citadel manage
to produce such detailed colourful graphics, and at such a speed?
     There are, in fact, two possible solutions, both of which involve
dealing with an area of memory known as screen memory. This is, however,
very complicated, and will be discussed further in the next article.

00000000  20 20 20 20 20 54 68 69  73 20 69 73 20 77 68 65  |     This is whe|
00000010  72 65 20 4d 4f 56 45 2c  20 44 52 41 57 20 61 6e  |re MOVE, DRAW an|
00000020  64 20 50 4c 4f 54 20 61  72 65 20 75 73 65 66 75  |d PLOT are usefu|
00000030  6c 2e 20 55 73 69 6e 67  20 74 68 65 73 65 20 63  |l. Using these c|
00000040  6f 6d 6d 61 6e 64 73 2c  0d 6c 69 6e 65 73 20 63  |ommands,.lines c|
00000050  61 6e 20 62 65 20 64 72  61 77 6e 20 61 63 72 6f  |an be drawn acro|
00000060  73 73 20 74 68 65 20 73  63 72 65 65 6e 2c 20 61  |ss the screen, a|
00000070  6e 64 2c 20 75 73 69 6e  67 20 50 4c 4f 54 2c 20  |nd, using PLOT, |
00000080  74 72 69 61 6e 67 6c 65  73 20 63 61 6e 20 62 65  |triangles can be|
00000090  0d 64 72 61 77 6e 2e 20  54 68 65 73 65 20 63 6f  |.drawn. These co|
000000a0  6d 6d 61 6e 64 73 20 61  72 65 20 63 6f 76 65 72  |mmands are cover|
000000b0  65 64 20 69 6e 20 74 68  65 20 47 72 61 70 68 69  |ed in the Graphi|
000000c0  63 73 20 63 68 61 70 74  65 72 20 6f 66 20 74 68  |cs chapter of th|
000000d0  65 20 75 73 65 72 0d 6d  61 6e 75 61 6c 2e 20 54  |e user.manual. T|
000000e0  68 65 20 6f 74 68 65 72  20 6d 61 6a 6f 72 20 61  |he other major a|
000000f0  64 76 61 6e 74 61 67 65  20 6f 66 20 74 68 65 73  |dvantage of thes|
00000100  65 20 67 72 61 70 68 69  63 73 20 63 6f 6d 6d 61  |e graphics comma|
00000110  6e 64 73 20 69 73 20 74  68 61 74 20 74 68 65 79  |nds is that they|
00000120  0d 63 61 6e 20 62 65 20  75 73 65 64 20 6e 6f 74  |.can be used not|
00000130  20 6a 75 73 74 20 74 6f  20 73 65 74 20 74 68 65  | just to set the|
00000140  20 63 6f 6c 6f 75 72 20  6f 66 20 61 6e 20 61 72  | colour of an ar|
00000150  65 61 2c 20 62 75 74 20  61 6c 73 6f 20 74 6f 20  |ea, but also to |
00000160  69 6e 76 65 72 74 20 69  74 2e 0d 54 68 65 20 47  |invert it..The G|
00000170  43 4f 4c 20 63 6f 6d 6d  61 6e 64 2c 20 77 68 69  |COL command, whi|
00000180  63 68 20 73 65 6c 65 63  74 73 20 74 68 65 20 63  |ch selects the c|
00000190  6f 6c 6f 75 72 20 69 6e  20 77 68 69 63 68 20 67  |olour in which g|
000001a0  72 61 70 68 69 63 73 20  61 72 65 0d 64 69 73 70  |raphics are.disp|
000001b0  6c 61 79 65 64 2c 20 74  61 6b 65 73 20 74 77 6f  |layed, takes two|
000001c0  20 70 61 72 61 6d 65 74  65 72 73 3a 0d 0d 47 43  | parameters:..GC|
000001d0  4f 4c 20 78 2c 63 0d 0d  63 20 69 73 20 74 68 65  |OL x,c..c is the|
000001e0  20 6e 65 77 20 63 6f 6c  6f 75 72 20 69 6e 20 77  | new colour in w|
000001f0  68 69 63 68 20 67 72 61  70 68 69 63 73 20 73 68  |hich graphics sh|
00000200  6f 75 6c 64 20 62 65 20  64 72 61 77 6e 2e 0d 78  |ould be drawn..x|
00000210  20 73 65 6c 65 63 74 73  20 68 6f 77 20 74 68 69  | selects how thi|
00000220  73 20 63 6f 6c 6f 75 72  20 73 68 6f 75 6c 64 20  |s colour should |
00000230  62 65 20 61 70 70 6c 79  65 64 3a 0d 0d 78 3d 30  |be applyed:..x=0|
00000240  20 6d 65 61 6e 73 20 74  6f 20 73 65 74 20 65 76  | means to set ev|
00000250  65 72 79 20 70 69 78 65  6c 20 74 6f 20 74 68 61  |ery pixel to tha|
00000260  74 20 63 6f 6c 6f 75 72  2c 20 72 65 67 61 72 64  |t colour, regard|
00000270  6c 65 73 73 20 6f 66 20  69 74 73 20 0d 70 72 65  |less of its .pre|
00000280  76 69 6f 75 73 20 63 6f  6c 6f 75 72 2e 0d 78 3d  |vious colour..x=|
00000290  31 20 6d 65 61 6e 73 20  74 6f 20 6d 69 78 20 74  |1 means to mix t|
000002a0  68 65 20 6c 69 67 68 74  20 66 72 6f 6d 20 74 68  |he light from th|
000002b0  65 20 70 69 78 65 6c 20  61 6c 72 65 61 64 79 20  |e pixel already |
000002c0  6f 6e 20 74 68 65 20 73  63 72 65 65 6e 20 0d 77  |on the screen .w|
000002d0  69 74 68 20 74 68 61 74  20 6f 66 20 74 68 65 20  |ith that of the |
000002e0  6e 65 77 20 63 6f 6c 6f  75 72 2e 20 46 6f 72 20  |new colour. For |
000002f0  65 78 61 6d 70 6c 65 2c  20 69 66 20 61 20 72 65  |example, if a re|
00000300  64 20 70 69 78 65 6c 20  69 73 20 73 65 74 20 0d  |d pixel is set .|
00000310  74 6f 20 62 6c 75 65 2c  20 74 68 65 20 72 65 64  |to blue, the red|
00000320  20 61 6e 64 20 62 6c 75  65 20 6d 69 78 20 74 6f  | and blue mix to|
00000330  20 66 6f 72 6d 20 70 75  72 70 6c 65 2e 0d 78 3d  | form purple..x=|
00000340  32 20 6d 65 61 6e 73 20  74 68 61 74 20 74 68 65  |2 means that the|
00000350  20 6c 69 67 68 74 20 66  72 6f 6d 20 74 68 65 20  | light from the |
00000360  70 69 78 65 6c 73 20 69  73 20 66 69 6c 74 65 72  |pixels is filter|
00000370  65 64 20 77 69 74 68 20  74 68 65 20 6e 65 77 20  |ed with the new |
00000380  0d 63 6f 6c 6f 75 72 2e  20 49 66 20 61 20 72 65  |.colour. If a re|
00000390  64 20 70 69 78 65 6c 20  69 73 20 73 65 74 20 74  |d pixel is set t|
000003a0  6f 20 62 6c 75 65 20 6e  6f 77 2c 20 69 74 20 69  |o blue now, it i|
000003b0  73 20 61 73 20 69 66 20  61 20 62 6c 75 65 20 0d  |s as if a blue .|
000003c0  66 69 6c 74 65 72 20 68  61 73 20 62 65 65 6e 20  |filter has been |
000003d0  70 6c 61 63 65 64 20 69  6e 20 66 72 6f 6e 74 20  |placed in front |
000003e0  6f 66 20 74 68 65 20 72  65 64 20 6c 69 67 68 74  |of the red light|
000003f0  2c 20 61 6e 64 20 74 68  65 20 0d 72 65 73 75 6c  |, and the .resul|
00000400  74 61 6e 74 20 63 6f 6c  6f 75 72 20 69 73 20 62  |tant colour is b|
00000410  6c 61 63 6b 20 28 72 65  64 20 6c 69 67 68 74 20  |lack (red light |
00000420  63 6f 6e 74 61 69 6e 73  20 6e 6f 20 62 6c 75 65  |contains no blue|
00000430  20 63 6f 6d 70 6f 6e 65  6e 74 29 2e 0d 78 3d 33  | component)..x=3|
00000440  20 6d 65 61 6e 73 20 74  6f 20 69 6e 76 65 72 74  | means to invert|
00000450  20 74 68 65 20 6f 6c 64  20 63 6f 6c 6f 75 72 20  | the old colour |
00000460  77 69 74 68 20 74 68 65  20 6e 65 77 20 63 6f 6c  |with the new col|
00000470  6f 75 72 2e 0d 78 3d 34  20 6d 65 61 6e 73 20 74  |our..x=4 means t|
00000480  6f 20 73 65 74 20 74 68  65 20 70 69 78 65 6c 73  |o set the pixels|
00000490  20 77 69 74 68 20 74 68  65 20 69 6e 76 65 72 73  | with the invers|
000004a0  65 20 6f 66 20 74 68 65  20 6e 65 77 20 63 6f 6c  |e of the new col|
000004b0  6f 75 72 20 0d 28 72 65  67 61 72 64 6c 65 73 73  |our .(regardless|
000004c0  20 6f 66 20 74 68 65 20  6f 6c 64 20 63 6f 6c 6f  | of the old colo|
000004d0  75 72 29 2e 0d 0d 20 20  20 20 20 4c 69 6e 65 73  |ur)...     Lines|
000004e0  20 6d 61 79 20 6e 6f 77  20 62 65 20 64 72 61 77  | may now be draw|
000004f0  6e 20 61 63 72 6f 73 73  20 74 68 65 20 73 63 72  |n across the scr|
00000500  65 65 6e 20 62 79 20 74  79 70 69 6e 67 3a 0d 0d  |een by typing:..|
00000510  4d 4f 56 45 20 78 2c 79  3a 44 52 41 57 20 78 62  |MOVE x,y:DRAW xb|
00000520  2c 79 62 0d 0d 57 68 65  72 65 3a 20 28 78 2c 79  |,yb..Where: (x,y|
00000530  29 20 20 20 3d 20 54 68  65 20 63 6f 2d 6f 72 64  |)   = The co-ord|
00000540  69 6e 61 74 65 20 6f 66  20 74 68 65 20 66 69 72  |inate of the fir|
00000550  73 74 20 70 6f 69 6e 74  20 6f 6e 20 74 68 65 20  |st point on the |
00000560  6c 69 6e 65 2e 0d 20 20  20 20 20 20 20 28 78 62  |line..       (xb|
00000570  2c 79 62 29 20 3d 20 54  68 61 74 20 6f 66 20 74  |,yb) = That of t|
00000580  68 65 20 6c 61 73 74 20  70 6f 69 6e 74 20 6f 6e  |he last point on|
00000590  20 74 68 65 20 6c 69 6e  65 2e 0d 0d 20 20 20 20  | the line...    |
000005a0  20 54 68 65 20 72 61 6e  67 65 20 6f 66 20 74 68  | The range of th|
000005b0  65 20 73 63 72 65 65 6e  20 69 73 20 61 6c 77 61  |e screen is alwa|
000005c0  79 73 20 31 32 38 30 20  70 69 78 65 6c 73 20 61  |ys 1280 pixels a|
000005d0  63 72 6f 73 73 2c 20 61  6e 64 20 31 30 32 34 20  |cross, and 1024 |
000005e0  70 69 78 65 6c 73 20 0d  64 6f 77 6e 2e 20 54 68  |pixels .down. Th|
000005f0  65 20 62 6f 74 74 6f 6d  20 6c 65 66 74 20 63 6f  |e bottom left co|
00000600  72 6e 65 72 20 69 73 20  70 6f 69 6e 74 20 28 30  |rner is point (0|
00000610  2c 30 29 2c 20 61 6e 64  20 74 68 65 20 74 6f 70  |,0), and the top|
00000620  20 72 69 67 68 74 20 63  6f 72 6e 65 72 20 69 73  | right corner is|
00000630  20 0d 28 31 32 38 30 2c  31 30 32 34 29 2e 20 4c  | .(1280,1024). L|
00000640  61 72 67 65 72 20 67 72  61 70 68 69 63 73 20 63  |arger graphics c|
00000650  61 6e 20 62 65 20 64 72  61 77 6e 20 75 73 69 6e  |an be drawn usin|
00000660  67 20 74 68 65 20 50 4c  4f 54 20 63 6f 6d 6d 61  |g the PLOT comma|
00000670  6e 64 2e 20 54 68 65 20  6d 6f 73 74 20 0d 63 6f  |nd. The most .co|
00000680  6d 6d 6f 6e 20 75 73 61  67 65 20 69 73 20 61 73  |mmon usage is as|
00000690  20 66 6f 6c 6c 6f 77 73  3a 0d 0d 4d 4f 56 45 20  | follows:..MOVE |
000006a0  78 2c 79 3a 20 4d 4f 56  45 20 78 62 2c 79 62 3a  |x,y: MOVE xb,yb:|
000006b0  50 4c 4f 54 20 38 35 2c  78 63 2c 79 63 0d 0d 20  |PLOT 85,xc,yc.. |
000006c0  20 20 20 20 54 68 69 73  20 70 6c 6f 74 73 20 61  |    This plots a|
000006d0  20 66 69 6c 6c 65 64 20  74 72 69 61 6e 67 6c 65  | filled triangle|
000006e0  20 77 69 74 68 20 63 6f  72 6e 65 72 73 20 61 74  | with corners at|
000006f0  20 28 78 2c 79 29 2c 20  28 78 62 2c 79 62 29 20  | (x,y), (xb,yb) |
00000700  61 6e 64 20 0d 28 78 63  2c 79 63 29 2e 20 50 4c  |and .(xc,yc). PL|
00000710  4f 54 20 61 6c 73 6f 20  68 61 73 20 6d 61 6e 79  |OT also has many|
00000720  20 6f 74 68 65 72 20 66  75 6e 63 74 69 6f 6e 73  | other functions|
00000730  20 2d 20 73 65 65 20 74  68 65 20 55 73 65 72 20  | - see the User |
00000740  47 75 69 64 65 20 66 6f  72 20 64 65 74 61 69 6c  |Guide for detail|
00000750  73 2e 0d 20 20 20 20 20  41 74 20 66 69 72 73 74  |s..     At first|
00000760  20 73 69 67 68 74 2c 20  69 74 20 6d 61 79 20 73  | sight, it may s|
00000770  65 65 6d 20 74 68 61 74  20 75 73 65 72 20 64 65  |eem that user de|
00000780  66 69 6e 65 64 20 63 68  61 72 61 63 74 65 72 73  |fined characters|
00000790  20 73 65 72 76 65 20 6e  6f 0d 70 75 72 70 6f 73  | serve no.purpos|
000007a0  65 20 6f 6e 63 65 20 61  20 70 72 6f 67 72 61 6d  |e once a program|
000007b0  6d 65 72 20 68 61 73 20  6c 65 61 72 6e 74 20 61  |mer has learnt a|
000007c0  62 6f 75 74 20 74 68 65  20 6d 6f 72 65 20 66 6c  |bout the more fl|
000007d0  65 78 69 62 6c 65 20 67  72 61 70 68 69 63 73 0d  |exible graphics.|
000007e0  63 6f 6d 6d 61 6e 64 73  2c 20 62 75 74 20 74 68  |commands, but th|
000007f0  69 73 20 69 73 20 6e 6f  74 20 74 68 65 20 63 61  |is is not the ca|
00000800  73 65 2e 20 49 66 20 79  6f 75 20 74 72 79 20 74  |se. If you try t|
00000810  6f 20 70 72 6f 64 75 63  65 20 64 65 74 61 69 6c  |o produce detail|
00000820  65 64 0d 67 72 61 70 68  69 63 73 20 75 73 69 6e  |ed.graphics usin|
00000830  67 20 4d 4f 56 45 20 61  6e 64 20 44 52 41 57 2c  |g MOVE and DRAW,|
00000840  20 79 6f 75 20 77 69 6c  6c 20 66 69 6e 64 20 74  | you will find t|
00000850  68 61 74 20 79 6f 75 72  20 70 72 6f 67 72 61 6d  |hat your program|
00000860  20 63 72 61 77 6c 73 0d  61 6c 6f 6e 67 20 61 74  | crawls.along at|
00000870  20 61 6e 20 75 6e 61 63  63 65 70 74 61 62 6c 65  | an unacceptable|
00000880  20 72 61 74 65 2e 20 55  73 65 72 20 64 65 66 69  | rate. User defi|
00000890  6e 65 64 20 63 68 61 72  61 63 74 65 72 73 2c 20  |ned characters, |
000008a0  6f 6e 20 74 68 65 20 6f  74 68 65 72 0d 68 61 6e  |on the other.han|
000008b0  64 2c 20 63 61 6e 20 70  72 6f 64 75 63 65 20 64  |d, can produce d|
000008c0  65 74 61 69 6c 20 71 75  69 63 6b 6c 79 2c 20 65  |etail quickly, e|
000008d0  73 70 65 63 69 61 6c 6c  79 20 69 66 20 74 68 65  |specially if the|
000008e0  20 70 61 74 74 65 72 6e  20 72 65 70 65 61 74 73  | pattern repeats|
000008f0  2c 20 73 6f 0d 74 68 61  74 20 6f 6e 65 20 63 68  |, so.that one ch|
00000900  61 72 61 63 74 65 72 20  64 65 66 69 6e 69 74 69  |aracter definiti|
00000910  6f 6e 20 63 61 6e 20 62  65 20 75 73 65 64 20 72  |on can be used r|
00000920  65 70 65 61 74 65 64 6c  79 20 69 6e 20 73 65 76  |epeatedly in sev|
00000930  65 72 61 6c 20 61 72 65  61 73 20 6f 66 0d 74 68  |eral areas of.th|
00000940  65 20 73 63 72 65 65 6e  2e 20 54 68 69 73 20 69  |e screen. This i|
00000950  73 20 64 65 6d 6f 6e 73  74 72 61 74 65 64 20 62  |s demonstrated b|
00000960  79 20 74 68 65 20 70 72  6f 67 72 61 6d 20 77 68  |y the program wh|
00000970  69 63 68 20 69 73 20 61  76 61 69 6c 61 62 6c 65  |ich is available|
00000980  20 61 74 20 74 68 65 0d  65 6e 64 20 6f 66 20 74  | at the.end of t|
00000990  68 65 20 74 75 74 6f 72  69 61 6c 2e 0d 20 20 20  |he tutorial..   |
000009a0  20 20 53 6f 2c 20 69 74  20 73 65 65 6d 73 20 74  |  So, it seems t|
000009b0  68 61 74 20 70 72 6f 67  72 61 6d 6d 65 72 73 20  |hat programmers |
000009c0  61 72 65 20 66 61 63 65  64 20 77 69 74 68 20 61  |are faced with a|
000009d0  20 64 69 66 66 69 63 75  6c 74 20 70 72 6f 62 6c  | difficult probl|
000009e0  65 6d 2e 0d 54 68 65 79  20 63 61 6e 20 75 73 65  |em..They can use|
000009f0  20 67 72 61 70 68 69 63  73 20 63 6f 6d 6d 61 6e  | graphics comman|
00000a00  64 73 20 61 6e 64 20 67  65 74 20 63 6f 6c 6f 75  |ds and get colou|
00000a10  72 2c 20 6f 72 20 74 68  65 79 20 63 61 6e 20 75  |r, or they can u|
00000a20  73 65 20 75 73 65 72 0d  64 65 66 69 6e 65 64 20  |se user.defined |
00000a30  63 68 61 72 61 63 74 65  72 73 20 61 6e 64 20 67  |characters and g|
00000a40  65 74 20 64 65 74 61 69  6c 2c 20 62 75 74 20 77  |et detail, but w|
00000a50  68 61 74 20 69 66 20 74  68 65 79 20 77 61 6e 74  |hat if they want|
00000a60  20 62 6f 74 68 20 61 74  20 74 68 65 20 73 61 6d  | both at the sam|
00000a70  65 0d 74 69 6d 65 3f 20  54 68 65 72 65 20 6d 75  |e.time? There mu|
00000a80  73 74 20 62 65 20 61 20  73 6f 6c 75 74 69 6f 6e  |st be a solution|
00000a90  20 2d 20 68 6f 77 20 65  6c 73 65 20 77 6f 75 6c  | - how else woul|
00000aa0  64 20 67 61 6d 65 73 20  6c 69 6b 65 20 43 69 74  |d games like Cit|
00000ab0  61 64 65 6c 20 6d 61 6e  61 67 65 0d 74 6f 20 70  |adel manage.to p|
00000ac0  72 6f 64 75 63 65 20 73  75 63 68 20 64 65 74 61  |roduce such deta|
00000ad0  69 6c 65 64 20 63 6f 6c  6f 75 72 66 75 6c 20 67  |iled colourful g|
00000ae0  72 61 70 68 69 63 73 2c  20 61 6e 64 20 61 74 20  |raphics, and at |
00000af0  73 75 63 68 20 61 20 73  70 65 65 64 3f 0d 20 20  |such a speed?.  |
00000b00  20 20 20 54 68 65 72 65  20 61 72 65 2c 20 69 6e  |   There are, in|
00000b10  20 66 61 63 74 2c 20 74  77 6f 20 70 6f 73 73 69  | fact, two possi|
00000b20  62 6c 65 20 73 6f 6c 75  74 69 6f 6e 73 2c 20 62  |ble solutions, b|
00000b30  6f 74 68 20 6f 66 20 77  68 69 63 68 20 69 6e 76  |oth of which inv|
00000b40  6f 6c 76 65 0d 64 65 61  6c 69 6e 67 20 77 69 74  |olve.dealing wit|
00000b50  68 20 61 6e 20 61 72 65  61 20 6f 66 20 6d 65 6d  |h an area of mem|
00000b60  6f 72 79 20 6b 6e 6f 77  6e 20 61 73 20 73 63 72  |ory known as scr|
00000b70  65 65 6e 20 6d 65 6d 6f  72 79 2e 20 54 68 69 73  |een memory. This|
00000b80  20 69 73 2c 20 68 6f 77  65 76 65 72 2c 0d 76 65  | is, however,.ve|
00000b90  72 79 20 63 6f 6d 70 6c  69 63 61 74 65 64 2c 20  |ry complicated, |
00000ba0  61 6e 64 20 77 69 6c 6c  20 62 65 20 64 69 73 63  |and will be disc|
00000bb0  75 73 73 65 64 20 66 75  72 74 68 65 72 20 69 6e  |ussed further in|
00000bc0  20 74 68 65 20 6e 65 78  74 20 61 72 74 69 63 6c  | the next articl|
00000bd0  65 2e 0d                                          |e..|
00000bd3
PT/+P3.m0
PT/+P3.m1
PT/+P3.m2
PT/+P3.m4
PT/+P3.m5

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