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-===== PART 03 : Lines and circles =====
-Greetings! This is the third part of the VGA Trainer series! Sorry it took so long to get out, but I had a running battle with the traffic department for three days to get my car registered, and then the MailBox
-went down. Ahh, well, life stinks. Anyway, today will do some things vital to most programs : Lines and circles.
-Watch out for next week's part : Virtual screens. The easy way to eliminate flicker, "doubled sprites", and subjecting the user to watch you building your screen. Almost every ASPHYXIA demo has used a virtual
-screen (with the exception of the SilkyDemo), so this is one to watch out for. I will also show you how to put all of these loose procedures into units.
-If you would like to contact me, or the team, there are many ways you  can do it :
-  - Write a message to Grant Smith in private mail here on the Mailbox BBS.
-  - Write a message here in the Programming conference here on the Mailbox (Preferred if you have a general programming query or problem others would benefit from)
-  - Write to ASPHYXIA on the ASPHYXIA BBS.
-  - Write to Denthor, Eze or Livewire on Connectix.
-  - Write to :
-<code>
-Grant Smith
-P.O.Box 270 Kloof
-</code>
-  - Call me (Grant Smith) at 73 2129 (leave a message if you call during varsity)
-NB : If you are a representative of a company or BBS, and want ASPHYXIA to do you a demo, leave mail to me; we can discuss it.
-NNB : If you have done/attempted a demo, SEND IT TO ME! We are feeling quite lonely and want to meet/help out/exchange code with other demo groups. What do you have to lose? Leave a message here and we can work out how to transfer it. We really want to hear from you!
-==== Circle Algorithim ====
-You all know what a circle looks like. But how do you draw one on the computer?
-You probably know circles drawn with the degrees at these points :
-<code>
-                              ▄█|█▄
-                             ███|███
-----+---- 90
-                             ███|███
-                              ▀█|█▀
-</code>
-Sorry about my ASCI ;-) ... anyway, Pascal doesn't work that way ... it
-works with radians instead of degrees. (You can convert radians to degrees,
-but I'm not going to go into that now. Note though that in pascal, the
-circle goes like this :
-<code>
-                              ▄█|█▄
-                             ███|███
-----+---- 0
-                             ███|███
-                              ▀█|█▀
-</code>
-Even so, we can still use the famous equations to draw our circle ...
-(You derive the following by using the theorem of our good friend Pythagoras)
-<code>
-                     Sin (deg) = Y/R
-                     Cos (deg) = X/R
-</code>
-(This is standard 8(?) maths ... if you haven't reached that level yet, take this to your dad, or if you get stuck leave me a message and I'll do a bit of basic Trig with you. I aim to please ;-))
-<code>
-Where Y = your Y-coord
-      X = your X-coord
-      R = your radius (the size of your circle)
-      deg = the degree
-</code>
-To simplify matters, we rewrite the equation to get our X and Y values :
-<code>
-                     Y = R*Sin(deg)
-                     X = R*Cos(deg)
-</code>
-This obviousy is perfect for us, because it gives us our X and Y co-ords to put into our putpixel routine (see Part 1). Because the Sin and Cos functions return a Real value, we use a round function to transform it
-into an Integer.
-<code pascal>
-     Procedure Circle (oX,oY,rad:integer;Col:Byte);
-     VAR deg:real;
-         X,Y:integer;
-     BEGIN
-       deg:=0;
-       repeat
-         X:=round(rad*COS (deg));
-         Y:=round(rad*sin (deg));
-         putpixel (x+ox,y+oy,Col);
-         deg:=deg+0.005;
-       until (deg>6.4);
-     END;
-</code>
-In the above example, the smaller the amount that deg is increased by,
-the closer the pixels in the circle will be, but the slower the procedure.
-.005 seem to be best for the 320x200 screen. NOTE : ASPHYXIA does not use
-this particular circle algorithm, ours is in assembly language, but this
-one should be fast enough for most. If it isn't, give us the stuff you are
-using it for and we'll give you ours.
-==== Line algorithms ====
-There are many ways to draw a line on the computer. I will describe one
-and give you two. (The second one you can figure out for yourselves; it
-is based on the first one but is faster)
-The first thing you need to do is pass what you want the line to look
-like to your line procedure. What I have done is said that x1,y1 is the
-first point on the screen, and x2,y2 is the second point. We also pass the
-color to the procedure. (Remember the screens top left hand corner is (0,0);
-see Part 1)
-Ie.            o  (X1,Y1)
-                ooooooooo
-                         ooooooooo
-                                  oooooooo  (X2,Y2)
-Again, sorry about my drawings ;-)
-To find the length of the line, we say the following :
-           XLength = ABS (x1-x2)
-           YLength = ABS (y1-y2)
-The ABS function means that whatever the result, it will give you an
-absolute, or posotive, answer. At this stage I set a variable stating
-wheter the difference between the two x's are negative, zero or posotive.
-(I do the same for the y's) If the difference is zero, I just use a loop
-keeping the two with the zero difference posotive, then exit.
-If neither the x's or y's have a zero difference, I calculate the X and Y
-slopes, using the following two equations :
-           Xslope = Xlength / Ylength
-           Yslope = Ylength / Xlength
-As you can see, the slopes are real numbers.
-NOTE : XSlope = 1 / YSlope
-Now, there are two ways of drawing the lines :
-           X = XSlope * Y
-           Y = YSlope * X
-The question is, which one to use? if you use the wrong one, your line
-will look like this :
-        o
-           o
-              o
-Instead of this :
-        ooo
-           ooo
-              ooo
-Well, the solution is as follows :
-                           *\``|``/*
-                           ***\|/***
-                           ----+----
-                           ***/|\***
-                           */``|``\*
-If the slope angle is in the area of the stars (*) then use the first
-equation, if it is in the other section (`) then use the second one.
-What you do is you calculate the variable on the left hand side by
-putting the variable on the right hand side in a loop and solving. Below
-is our finished line routine :
-<code pascal>
-Procedure Line (x1,y1,x2,y2:integer;col:byte);
-VAR x,y,xlength,ylength,dx,dy:integer;
-    xslope,yslope:real;
-BEGIN
-  xlength:=abs (x1-x2);
-  if (x1-x2)<0 then dx:=-1;
-  if (x1-x2)=0 then dx:=0;
-  if (x1-x2)>0 then dx:=+1;
-  ylength:=abs (y1-y2);
-  if (y1-y2)<0 then dy:=-1;
-  if (y1-y2)=0 then dy:=0;
-  if (y1-y2)>0 then dy:=+1;
-  if (dy=0) then BEGIN
-    if dx<0 then for x:=x1 to x2 do
-      putpixel (x,y1,col);
-    if dx>0 then for x:=x2 to x1 do
-      putpixel (x,y1,col);
-    exit;
-  END;
-  if (dx=0) then BEGIN
-    if dy<0 then for y:=y1 to y2 do
-      putpixel (x1,y,col);
-    if dy>0 then for y:=y2 to y1 do
-      putpixel (x1,y,col);
-    exit;
-  END;
-  xslope:=xlength/ylength;
-  yslope:=ylength/xlength;
-  if (yslope/xslope<1) and (yslope/xslope>-1) then BEGIN
-    if dx<0 then for x:=x1 to x2 do BEGIN
-                   y:= round (yslope*x);
-                   putpixel (x,y,col);
-                 END;
-    if dx>0 then for x:=x2 to x1 do BEGIN
-                   y:= round (yslope*x);
-                   putpixel (x,y,col);
-                 END;
-  END
-  ELSE
-  BEGIN
-    if dy<0 then for y:=y1 to y2 do BEGIN
-                   x:= round (xslope*y);
-                   putpixel (x,y,col);
-                 END;
-    if dy>0 then for y:=y2 to y1 do BEGIN
-                   x:= round (xslope*y);
-                   putpixel (x,y,col);
-                 END;
-  END;
-END;
-</code>
-Quite big, isn't it? Here is a much shorter way of doing much the same
-thing :
-<code pascal>
-function sgn(a:real):integer;
-begin
-     if a>0 then sgn:=+1;
-     if a<0 then sgn:=-1;
-     if a=0 then sgn:=0;
-end;
-procedure line(a,b,c,d,col:integer);
-var u,s,v,d1x,d1y,d2x,d2y,m,n:real;
-    i:integer;
-begin
-     u:= c - a;
-     v:= d - b;
-     d1x:= SGN(u);
-     d1y:= SGN(v);
-     d2x:= SGN(u);
-     d2y:= 0;
-     m:= ABS(u);
-     n := ABS(v);
-     IF NOT (M>N) then
-     BEGIN
-          d2x := 0 ;
-          d2y := SGN(v);
-          m := ABS(v);
-          n := ABS(u);
-     END;
-     s := INT(m / 2);
-     FOR i := 0 TO round(m) DO
-     BEGIN
-          putpixel(a,b,col);
-          s := s + n;
-          IF not (s<m) THEN
-          BEGIN
-               s := s - m;
-               a:= a +round(d1x);
-               b := b + round(d1y);
-          END
-          ELSE
-          BEGIN
-               a := a + round(d2x);
-               b := b + round(d2y);
-          END;
-     end;
-END;
-</code>
-This routine is very fast, and should meet almost all of your requirements (ASPHYXIA used it for quite a while before we made our new one.)
-In the end program, both the new line routine and the circle routine are tested. A few of the procedures of the first parts are also used.
-Line and circle routines may seem like fairly trivial things, but they are a vital component of many programs, and you may like to look up other methods of drawing them in books in the library (I know that here at the
-varsity they have books for doing this kind of stuff all over the place) A good line routine to look out for is the Bressenhams line routine ... there is a Bressenhams circle routine too ... I have documentaiton for them
-if anybody is interested, they are by far some of the fastest routines you will use.
-==== In closing ====
-Varsity has started again, so I am (shock) going to bed before three in the morning, so my quote this week wasn't written in the same wasted way my last weeks one was (For last week's one, I had gotten 8 hours sleep in
-days, and thought up and wrote the quote at 2:23 am before I fell asleep.)
-<code>
-        [  "What does it do?" she asks.
-           "It's a computer," he replies.
-           "Yes, dear, but what does it do?"
-           "It ..er.. computes! It's a computer."
-           "What does it compute?"
-           "What? Er? Um. Numbers! Yes, numbers!" He smiles worriedly.
-           "Why?"
-           "Why? Well ..um.. why?" He starts to sweat.
-           "I mean, is it just something to dust around, or does it actually do something useful?"
-           "Um...you can call other computers with it!" Hope lights up his eyes. "So you can get programs from other computers!"
-           "I see. Tell me, what do these programs do?"
-           "Do? I don't think I fol..."
-           "I see. They compute. Numbers. For no particular reason." He withers under her gaze.
-           "Yes, but..."
-           She smiles, and he trails off, defeated. She takes another look at the thing. "Although," she says, with a strange look in her eyes. He looks up, an insane look of hope on his face. "Does it come in pink?" she asks.
-                                                     - Grant Smith
-                                                        Tue 27 July, 1993
-:35 pm.
-</code>
-==== Code Source ====
-=== PASCAL ===
-<code pascal>
-(*****************************************************************************)
-(*                                                                           *)
-(* TUT3.PAS - VGA Trainer Program 3 (in Pascal)                              *)
-(*                                                                           *)
-(* "The VGA Trainer Program" is written by Denthor of Asphyxia.  However it  *)
-(* was limited to Pascal only in its first run.  All I have done is taken    *)
-(* his original release, translated it to C++, and touched up a few things.  *)
-(* I take absolutely no credit for the concepts presented in this code, and  *)
-(* am NOT the person to ask for help if you are having trouble.              *)
-(*                                                                           *)
-(* Program Notes : This program presents many new concepts, including:       *)
-(*                 Cirle and Line algorithms.                                *)
-(*                                                                           *)
-(* Author        : Grant Smith (Denthor)  - denthor@beastie.cs.und.ac.za     *)
-(*                                                                           *)
-(*****************************************************************************)
-{$X+}
-USES crt;
-CONST VGA = $a000;
-VAR loop1:integer;
-    Pall : Array [1..199,1..3] of byte;
-      { This is our temporary pallette. We ony use colors 1 to 199, so we
-        only have variables for those ones. }
-{ÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄ}
-Procedure SetMCGA;  { This procedure gets you into 320x200x256 mode. }
-BEGIN
-  asm
-     mov        ax,0013h
-     int        10h
-  end;
-END;
-{ÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄ}
-Procedure SetText;  { This procedure returns you to text mode.  }
-BEGIN
-  asm
-     mov        ax,0003h
-     int        10h
-  end;
-END;
-{ÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄ}
-Procedure Putpixel (X,Y : Integer; Col : Byte);
-  { This puts a pixel on the screen by writing directly to memory. }
-BEGIN
-  Mem [VGA:X+(Y*320)]:=Col;
-END;
-{ÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄ}
-procedure WaitRetrace; assembler;
-label
-  l1, l2;
-asm
-    mov dx,3DAh
-l1:
-    in al,dx
-    and al,08h
-    jnz l1
-l2:
-    in al,dx
-    and al,08h
-    jz  l2
-end;
-{ÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄ}
-Procedure Pal(ColorNo : Byte; R,G,B : Byte);
-  { This sets the Red, Green and Blue values of a certain color }
-Begin
-   Port[$3c8] := ColorNo;
-   Port[$3c9] := R;
-   Port[$3c9] := G;
-   Port[$3c9] := B;
-End;
-{ÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄ}
-Procedure Circle (X,Y,rad:integer;Col:Byte);
-  { This draws a circle with centre X,Y, with Rad as it's radius }
-VAR deg:real;
-BEGIN
-  deg:=0;
-  repeat
-    X:=round(rad*COS (deg));
-    Y:=round(rad*sin (deg));
-    putpixel (x+160,y+100,col);
-    deg:=deg+0.005;
-  until (deg>6.4);
-END;
-{ÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄ}
-Procedure Line2 (x1,y1,x2,y2:integer;col:byte);
-  { This draws a line from x1,y1 to x2,y2 using the first method }
-VAR x,y,xlength,ylength,dx,dy:integer;
-    xslope,yslope:real;
-BEGIN
-  xlength:=abs (x1-x2);
-  if (x1-x2)<0 then dx:=-1;
-  if (x1-x2)=0 then dx:=0;
-  if (x1-x2)>0 then dx:=+1;
-  ylength:=abs (y1-y2);
-  if (y1-y2)<0 then dy:=-1;
-  if (y1-y2)=0 then dy:=0;
-  if (y1-y2)>0 then dy:=+1;
-  if (dy=0) then BEGIN
-    if dx<0 then for x:=x1 to x2 do
-      putpixel (x,y1,col);
-    if dx>0 then for x:=x2 to x1 do
-      putpixel (x,y1,col);
-    exit;
-  END;
-  if (dx=0) then BEGIN
-    if dy<0 then for y:=y1 to y2 do
-      putpixel (x1,y,col);
-    if dy>0 then for y:=y2 to y1 do
-      putpixel (x1,y,col);
-    exit;
-  END;
-  xslope:=xlength/ylength;
-  yslope:=ylength/xlength;
-  if (yslope/xslope<1) and (yslope/xslope>-1) then BEGIN
-    if dx<0 then for x:=x1 to x2 do BEGIN
-                   y:= round (yslope*x);
-                   putpixel (x,y,col);
-                 END;
-    if dx>0 then for x:=x2 to x1 do BEGIN
-                   y:= round (yslope*x);
-                   putpixel (x,y,col);
-                 END;
-  END
-  ELSE
-  BEGIN
-    if dy<0 then for y:=y1 to y2 do BEGIN
-                   x:= round (xslope*y);
-                   putpixel (x,y,col);
-                 END;
-    if dy>0 then for y:=y2 to y1 do BEGIN
-                   x:= round (xslope*y);
-                   putpixel (x,y,col);
-                 END;
-  END;
-END;
-{ÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄ}
-procedure line(a,b,c,d,col:integer);
-  { This draws a line from x1,y1 to x2,y2 using the first method }
-    function sgn(a:real):integer;
-    begin
-         if a>0 then sgn:=+1;
-         if a<0 then sgn:=-1;
-         if a=0 then sgn:=0;
-    end;
-var u,s,v,d1x,d1y,d2x,d2y,m,n:real;
-    i:integer;
-begin
-     u:= c - a;
-     v:= d - b;
-     d1x:= SGN(u);
-     d1y:= SGN(v);
-     d2x:= SGN(u);
-     d2y:= 0;
-     m:= ABS(u);
-     n := ABS(v);
-     IF NOT (M>N) then
-     BEGIN
-          d2x := 0 ;
-          d2y := SGN(v);
-          m := ABS(v);
-          n := ABS(u);
-     END;
-     s := INT(m / 2);
-     FOR i := 0 TO round(m) DO
-     BEGIN
-          putpixel(a,b,col);
-          s := s + n;
-          IF not (s<m) THEN
-          BEGIN
-               s := s - m;
-               a:= a +round(d1x);
-               b := b + round(d1y);
-          END
-          ELSE
-          BEGIN
-               a := a + round(d2x);
-               b := b + round(d2y);
-          END;
-     end;
-END;
-{ÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄ}
-Procedure PalPlay;
-  { This procedure mucks about with our "virtual pallette", then shoves it
-    to screen. }
-Var Tmp : Array[1..3] of Byte;
-  { This is used as a "temporary color" in our pallette }
-    loop1 : Integer;
-BEGIN
-   Move(Pall[199],Tmp,3);
-     { This copies color 199 from our virtual pallette to the Tmp variable }
-   Move(Pall[1],Pall[2],198*3);
-     { This moves the entire virtual pallette up one color }
-   Move(Tmp,Pall[1],3);
-     { This copies the Tmp variable to the bottom of the virtual pallette }
-   WaitRetrace;
-   For loop1:=1 to 199 do
-     pal (loop1,pall[loop1,1],pall[loop1,2],pall[loop1,3]);
-END;
-BEGIN
-  ClrScr;
-  Writeln ('This sample program will test out our line and circle algorithms.');
-  Writeln ('In the first part, many circles will be draw creating (hopefully)');
-  Writeln ('a "tunnel" effect. I will the rotate the pallete to make it look');
-  Writeln ('nice. I will then draw some lines and rotate the pallette on them');
-  Writeln ('too. Note : I am using the slower (first) line algorithm (in');
-  Writeln ('procedure line2). Change it to Procedure Line and it will be using');
-  Writeln ('the second line routine. NB : For descriptions on how pallette works');
-  Writeln ('have a look at part two of this series; I won''t re-explain it here.');
-  Writeln;
-  Writeln ('Remember to send me any work you have done, I am most eager to help.');
-  Writeln; Writeln;
-  Writeln ('Hit any key to continue ...');
-  Readkey;
-  setmcga;
-  For Loop1 := 1 to 199 do BEGIN
-    Pall[Loop1,1] := Loop1 mod 30+33;
-    Pall[Loop1,2] := 0;
-    Pall[Loop1,3] := 0;
-  END;
-       { This sets colors 1 to 199 to values between 33 to 63. The MOD
-         function gives you the remainder of a division, ie. 105 mod 10 = 5 }
-   WaitRetrace;
-   For loop1:=1 to 199 do
-     pal (loop1,pall[loop1,1],pall[loop1,2],pall[loop1,3]);
-        { This sets the true pallette to variable Pall }
-  for loop1:=1 to 90 do
-    circle (160,100,loop1,loop1);
-       { This draws 90 circles all with centres at 160,100; with increasing
-         radii and colors. }
-  Repeat
-    PalPlay;
-  Until keypressed;
-  Readkey;
-  for loop1:=1 to 199 do
-    line2 (0,1,319,loop1,loop1);   { *** Replace Line2 with Line to use the
-                                         second line algorithm *** }
-       { This draws 199 lines, all starting at 0,1 }
-  Repeat
-    PalPlay;
-  Until keypressed;
-  readkey;
-  SetText;
-  Writeln ('All done. Okay, so maybe it wasn''t a tunnel effect, but you get the');
-  Writeln ('general idea ;-) This concludes the third sample program in the ASPHYXIA');
-  Writeln ('Training series. You may reach DENTHOR under the name of GRANT SMITH');
-  Writeln ('on the MailBox BBS, or leave a message to ASPHYXIA on the ASPHYXIA BBS.');
-  Writeln ('Get the numbers from Roblist, or write to :');
-  Writeln ('             Grant Smith');
-  Writeln ('             P.O. Box 270');
-  Writeln ('             Kloof');
-  Writeln ('             3640');
-  Writeln ('I hope to hear from you soon!');
-  Writeln; Writeln;
-  Write   ('Hit any key to exit ...');
-  Readkey;
-END.
-</code>
-=== C ===
-<code c>
-/////////////////////////////////////////////////////////////////////////////
-//                                                                         //
-// TUTPROG3.CPP - VGA Trainer Program 3 (in Turbo C++ 3.0)                 //
-//                                                                         //
-// "The VGA Trainer Program" is written by Denthor of Asphyxia. However it //
-// was limited to Pascal only in its first run.  All I have done is taken  //
-// his original release, translated it to C++ and touched up a few things. //
-// I take absolutely no credit for the concepts presented in this code and //
-// am NOT the person to ask for help if you are having trouble.            //
-//                                                                         //
-// Program Notes : This program presents many new concepts, including:     //
-//                 Cirle and Line algorithms.                              //
-//                                                                         //
-//                 If you are compiling this code command line, be sure to //
-//                 use the "-ml" parameter (large memory model).           //
-//                 Otherwise, the program will compile and link, but will  //
-//                 lock up your system.                                    //
-//                                                                         //
-// Author        : Grant Smith (Denthor) - denthor@beastie.cs.und.ac.za    //
-// Translator    : Christopher G. Mann   - r3cgm@dax.cc.uakron.edu         //
-//                                                                         //
-// Last Modified : December 7, 1994                                        //
-//                                                                         //
-/////////////////////////////////////////////////////////////////////////////
-//               //
-// INCLUDE FILES //
-//               //
-  #include <conio.h>
-			  // getch(), clrscr(), kbhit()
-  #include <dos.h>
-			  // MK_FP, Geninterrupt()
-  #include <math.h>
-			  // floor(), ceil(), abs(), sin(), cos()
-  #include <iostream.h>
-			  // cout, endl, memset(), _fmemset()
-//                     //
-// FUNCTION PROTOTYPES //
-//                     //
-  // MODE SETTING FUNCTIONS
-  void SetMCGA();
-  void SetText();
-  // PALLETTE FUNCTIONS
-  void Pal    (unsigned char ColorNo,  unsigned char R,
-	       unsigned char G,        unsigned char B);
-  void PalPlay();
-  // SMALL UTILITY FUNCTIONS
-  int  sgn    (long a);
-  int  round  (long a);
-  // DRAWING FUNCTIONS
-  void Putpixel (int  x, int  y, unsigned char Col);
-  void Line     (int  a, int  b, int   c, int  d, int col);
-  void Line2    (int x1, int y1, int  x2, int y2, int col);
-  void Circle   (int  X, int  Y, int rad, int col);
-  void WaitRetrace();
-//                              //
-// GLOBAL VARIABLE DECLARATIONS //
-//                              //
-  // declare a pointer to the offset of VGA memory
-  unsigned char *vga = (unsigned char *) MK_FP(0xA000, 0);
-  // This declares the PALL variable. 0 to 255 signifies the colors of the
-  // pallette, 1 to 3 signifies the Red, Green and Blue values. I am
-  // going to use this as a sort of "virtual pallette", and alter it
-  // as much as I want, then suddenly bang it to screen. Pall2 is used
-  // to "remember" the origional pallette so that we can restore it at
-  // the end of the program. */
-  unsigned char Pall[256][3], Pall2[256][3];
-///////////////////////////////////////////////////////////////////////////////
-//                                                                           //
-//                                MAIN FUNCTION                              //
-//                                                                           //
-///////////////////////////////////////////////////////////////////////////////
-void main() {
-  clrscr();
-  cout
-    << "This sample program will test out our line and circle algorithms.\n"
-    << "In the first part, many circles will be draw creating (hopefully)\n"
-    << "a ""tunnel"" effect. I will the rotate the pallete to make it look\n"
-    << "nice. I will then draw some lines and rotate the pallette on them\n"
-    << "too. Note : I am using the slower (first) line algorithm (in\n"
-    << "procedure line2). Change it to Procedure Line and it will be using\n"
-    << "the second line routine. NB : For descriptions on how pallette works\n"
-    << "have a look at part two of this series; I won''t re-explain it here."
-    << endl << endl;
-  cout
-    << "Remember to send me any work you have done, I am most eager to help."
-    << endl << endl;
-  cout
-    << "Hit any key to continue ...";
-  getch();
-  SetMCGA();
-  // This sets colors 1 to 199 to values between 33 to 63. The MOD
-  // function gives you the remainder of a division, ie. 105 mod 10 = 5 }
-  for (int loop1=1; loop1<200; loop1++) {
-    Pall[loop1][0] = (loop1 % 30) + 33;
-    Pall[loop1][1] = 0;
-    Pall[loop1][2] = 0;
-  }
-  WaitRetrace();
-  // This sets the true pallette to variable Pall
-  for (loop1=1; loop1<200; loop1++)
-    Pal(loop1, Pall[loop1][0], Pall[loop1][1], Pall[loop1][2]);
-  // This draws 90 circles all with centers at 160,100 with increasing
-  // radii and colors.
-  for (loop1=1; loop1<91; loop1++)
-    Circle(160, 100, loop1, loop1);
-  // wait until a key is pressed
-  while (!kbhit()) PalPlay();
-  // make sure to clear the keyboard buffer
-  getch();
-  // This draws 199 lines, all starting at 0,1
-  for (loop1=1; loop1<200; loop1++)
-    Line2 (0,1,319,loop1,loop1);   // *** Replace Line2 with Line to use the
-				   // second line algorithm ***
-  while (!kbhit()) PalPlay();
-  getch();
-  getch();
-  SetText();
-  cout
-    << "All done. Okay, so maybe it wasn''t a tunnel effect, but you get the\n"
-    << "general idea ;-) This concludes the third sample program in the ASPHYXIA\n"
-    << "Training series. You may reach DENTHOR under the name of GRANT SMITH\n"
-    << "on the MailBox BBS, or leave a message to ASPHYXIA on the ASPHYXIA BBS\n"
-    << "Get the numbers from Roblist, or write to :\n"
-    << "             Grant Smith\n"
-    << "             P.O. Box 270\n"
-    << "             Kloof\n"
-    << "             3640\n" << endl;
-  cout << "I hope to hear from you soon!" << endl << endl;
-  cout << "Hit any key to exit ...";
-  getch();
-}
-/////////////////////////////////////////////////////////////////////////////
-//                                                                         //
-// SetMCGA() - This function gets you into 320x200x256 mode.               //
-//                                                                         //
-/////////////////////////////////////////////////////////////////////////////
-void SetMCGA() {
-  _AX = 0x0013;
-  geninterrupt (0x10);
-}
-/////////////////////////////////////////////////////////////////////////////
-//                                                                         //
-// SetText() - This function gets you into text mode.                      //
-//                                                                         //
-/////////////////////////////////////////////////////////////////////////////
-void SetText() {
-  _AX = 0x0003;
-  geninterrupt (0x10);
-}
-/////////////////////////////////////////////////////////////////////////////
-//                                                                         //
-// Pal() - This sets the Red, Green, and Blue values of a certain color.   //
-//                                                                         //
-/////////////////////////////////////////////////////////////////////////////
-void Pal(unsigned char ColorNo, unsigned char R,
-	 unsigned char G,       unsigned char B) {
-  outp (0x03C8,ColorNo); // here is the pallette color I want to set
-  outp (0x03C9,R);
-  outp (0x03C9,G);
-  outp (0x03C9,B);
-}
-/////////////////////////////////////////////////////////////////////////////
-//                                                                         //
-// PalPlay() - This function mucks about with our "virtual pallette", then //
-//             shoves it to the screen.                                    //
-//                                                                         //
-/////////////////////////////////////////////////////////////////////////////
-void PalPlay() {
-unsigned char Tmp[3];
-  // This copies color 199 from our virtual pallette to the Tmp variable.
-  _fmemmove(Tmp,Pall[199],3);
-  // This moves the entire virtual pallette up one color.
-  _fmemmove(Pall[2],Pall[1],199*3);
-  // This copies the Tmp variable to the bottom of the virtual pallette.
-  // Don't change 0: leave this always black to not change overscan color.
-  _fmemmove(Pall[1],Tmp,3);
-  WaitRetrace();
-  for (int loop1=0;loop1<256;loop1++)
-   Pal(loop1,Pall[loop1][0], Pall[loop1][1], Pall[loop1][2]);
-}
-/////////////////////////////////////////////////////////////////////////////
-//                                                                         //
-// sgn() - This function is used by Line() to determine the sign of a long //
-//                                                                         //
-/////////////////////////////////////////////////////////////////////////////
-int sgn (long a) {
-  if (a > 0) return +1;
-  else if (a < 0) return -1;
-  else return 0;
-}
-/////////////////////////////////////////////////////////////////////////////
-//                                                                         //
-// round() - This function is used by Line() to round a long to the        //
-//           nearest integer.                                              //
-//                                                                         //
-/////////////////////////////////////////////////////////////////////////////
-int round (long a) {
-  if ( (a - (int)a) < 0.5) return floor(a);
-    else return ceil(a);
-}
-/////////////////////////////////////////////////////////////////////////////
-//                                                                         //
-// Putpixel() - This puts a pixel on the screen by writing directly to     //
-//              memory.                                                    //
-//                                                                         //
-/////////////////////////////////////////////////////////////////////////////
-void Putpixel (int x, int y, unsigned char Col) {
-  memset(vga+(x+(y*320)),Col,1);
-}
-/////////////////////////////////////////////////////////////////////////////
-//                                                                         //
-// Line() - This draws a line from a,b to c,d of color col.                //
-//          This function will be explained in more detail in tut3new.zip  //
-//                                                                         //
-/////////////////////////////////////////////////////////////////////////////
-void Line(int a, int b, int c, int d, int col) {
-  long u,s,v,d1x,d1y,d2x,d2y,m,n;
-  int  i;
-  u   = c-a;      // x2-x1
-  v   = d-b;      // y2-y1
-  d1x = sgn(u);   // d1x is the sign of u (x2-x1) (VALUE -1,0,1)
-  d1y = sgn(v);   // d1y is the sign of v (y2-y1) (VALUE -1,0,1)
-  d2x = sgn(u);   // d2x is the sign of u (x2-x1) (VALUE -1,0,1)
-  d2y = 0;
-  m   = abs(u);   // m is the distance between x1 and x2
-  n   = abs(v);   // n is the distance between y1 and y2
-  if (m<=n) {     // if the x distance is greater than the y distance
-    d2x = 0;
-    d2y = sgn(v); // d2y is the sign of v (x2-x1) (VALUE -1,0,1)
-    m   = abs(v); // m is the distance between y1 and y2
-    n   = abs(u); // n is the distance between x1 and x2
-  }
-  s = (int)(m / 2); // s is the m distance (either x or y) divided by 2
-  for (i=0;i<round(m);i++) { // repeat this loop until it
-			     // is = to m (y or x distance)
-    Putpixel(a,b,col);       // plot a pixel at the original x1, y1
-    s += n;                  // add n (dis of x or y) to s (dis of x of y)
-    if (s >= m) {            // if s is >= m (distance between y1 and y2)
-      s -= m;
-      a += d1x;
-      b += d1y;
-    }
-    else {
-      a += d2x;
-      b += d2y;
-    }
-  }
-}
-/////////////////////////////////////////////////////////////////////////////
-//                                                                         //
-// Line2() - This function draws a line from x1,y1 to x2,y2 using the      //
-//           first method.                                                 //
-//                                                                         //
-/////////////////////////////////////////////////////////////////////////////
-void Line2(int x1, int y1, int x2, int y2, int col) {
-  int   x, y, xlength, ylength, dx, dy;
-  float xslope, yslope;
-  xlength = abs(x1-x2);
-  if ((x1-x2)  < 0) dx = -1;
-  if ((x1-x2) == 0) dx =  0;
-  if ((x1-x2)  > 0) dx = +1;
-  ylength = abs(y1-y2);
-  if ((y1-y2)  < 0) dy = -1;
-  if ((y1-y2) == 0) dy =  0;
-  if ((y1-y2)  > 0) dy = +1;
-  if (dy == 0) {
-    if (dx < 0)
-      for (x=x1; x<x2+1; x++)
-	Putpixel (x,y1,col);
-    if (dx > 0)
-      for (x=x2; x<x1+1; x++)
-	Putpixel (x,y1,col);
-  }
-  if (dx == 0) {
-    if (dy < 0)
-      for (y=y1; y<y2+1; y++)
-	Putpixel (x1,y,col);
-    if (dy > 0)
-      for (y=y2; y<y1+1; y++)
-	Putpixel (x1,y,col);
-  }
-  if ((xlength != 0) && (ylength != 0)) {
-    xslope = (float)xlength/(float)ylength;
-    yslope = (float)ylength/(float)xlength;
-  }
-  else {
-    xslope = 0.0;
-    yslope = 0.0;
-  }
-  if ((xslope != 0) && (yslope != 0) &&
-      (yslope/xslope < 1) && (yslope/xslope > -1)) {
-    if (dx < 0)
-      for (x=x1; x<x2+1; x++) {
-	y = round (yslope*x);
-	Putpixel (x,y,col);
-      }
-    if (dx > 0)
-      for (x=x2; x<x1+1; x++) {
-	y = round (yslope*x);
-	Putpixel (x,y,col);
-      }
-  }
-  else {
-    if (dy < 0)
-      for (y=x1; y<x2+1; y++) {
-	x = round (xslope*y);
-	Putpixel (x,y,col);
-      }
-    if (dy > 0)
-      for (y=x2; y<x1+1; y++) {
-	x = round (xslope*y);
-	Putpixel (x,y,col);
-      }
-  }
-}
-/////////////////////////////////////////////////////////////////////////////
-//                                                                         //
-// Circle() - This draws a circle with center X,Y, with Rad as its radius. //
-//                                                                         //
-/////////////////////////////////////////////////////////////////////////////
-void Circle(int X, int Y, int rad, int col) {
-  float deg = 0;
-  do {
-    X = round(rad * cos(deg));
-    Y = round(rad * sin(deg));
-    Putpixel (X+160, Y+100, col);
-    deg += 0.005;
-  }
-  while (deg <= 6.4);
-}
-/////////////////////////////////////////////////////////////////////////////
-//                                                                         //
-// WaitRetrace() - This waits until you are in a Verticle Retrace.         //
-//                                                                         //
-/////////////////////////////////////////////////////////////////////////////
-void WaitRetrace() {
-  _DX = 0x03DA;
-  l1: asm {
-	in  al,dx;
-	and al,0x08;
-	jnz l1;
-      }
-  l2: asm {
-	in  al,dx;
-	and al,0x08;
-	jz  l2;
-      }
-}
-</code>
-<nspages back2root/archives/denthor -simpleList -title -h1 -exclude:start -textPages="Denthor VGA Trainer">

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