Learn how to make fire in 13H mode in PASCAL 7

Learn how to make fire in 13H mode in PASCAL 7 for your own pleasure!!

@DrWatson

Published in

atari

· 24 Nov 2023

fire

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  /-\--------/-/--ANuBiS DeMo TUtORS--/-/--------/-\ 
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                   #Issue 2 :  Fire 
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                By: Barbatruc / Anubis 
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Introduction

Hi folks! Here is the second part of Anubis demo tutorial. I would give my cooperation to this group more than ever and here is a way I find to. Maybe it will work, maybe not... but anyway ;) I have some planing for this summer but, I can't forget to code and compose! Here is a little production coming from me and I hope you'll enjoy it. What I'll teach today is Fire Effect, which one of the first effect I worked on when I was a beginner. Now, let's start. All sample codes are in PASCAL 7.

First, you need to clean a 64000 bytes buffer.

var vscreen:array[0..63999] of bytes;

Creates a palette of color in the fire range with some red and orange colors:

(some procedures are different, here is the first one I learned)

procedure setpalette; 
var i:integer; 
begin 
 for i:=0 to 128 do begin 
  {first 128 colors} 
  port[$3C8]=i; {which mean that color i is set at port 3C8h} 
  port[$3C9]=i div 2; {red value for color i} 
  port[$3C9]=0; {green value} 
  port[$3C9]=0; {blue value} 

  {next 128 colors (128..255)} 
  port[$3C8]=128+i; 
  port[$3C9]=63; 
  port[$3C9]=i div 2; 
  port[$3C9]=0; 
 end 
end;

Now that you have your palette and your buffer, you need to code the fire in your buffer. The procedure is simple. To know the color of a pixel, you need to add the pixel which is at north, the other at south-west, south-east and south. After this divide these pixels by 4, which will never give you a number higher that 255 (sure, the max color number is 255).

Procedure codefire; 
var w:word; {we need to go higher than 32768, we do not use integer} 
begin 
 for w:=320 to 63679 do 
  buffer[w]=(buffer[w-320]+buffer[w+321]+buffer[w+320]+buffer[w+319]) div 4; 
end;

But if your buffer was cleaned, how do the fire will appear? For this, we do a simple procedure which add colored pixel at the bottom of the screen:

procedure bottomline; 
var i:integer; 
begin 
 for i:=0 to 319 do 
  buffer[63680+i]:=random(2)*255; 
end;

which will add colored pixel on the last line of the screen. Codefire's procedure was calculating the color of each pixels from 320 to 63679. I don't know why, but in PASCAL it seems that the buffer flicks a little bit and strange colors appears so it makes a fire which not really interesting to see.

Try it by yourself!

Now that you have all these procedures, we need to put the buffer in the video memory.

move(buffer,mem[$A000:0],64000);

An asm procedure will do the same thing but faster.

Now, here is a simple code that you can use to make a fire (in PASCAL). Use it at your own risk. I'm not responsible of any damages that it could cause to your machine.

{ 
 beginning of the code 
 Fire effect, by Barbatruc / Anubis 
 (C) 1998 Anubis prod. All rights reserved 
} 
program phire; 

var vscreen:array[0..63999] of byte; 
    W:word; 

procedure setMCGA; 
begin 
 asm 
  MOV AX,13h 
  INT 10h 
 end 
end; 

procedure setTEXT; 
begin 
 asm 
  MOV AX,3h 
  INT 10h 
 end 
end; 

procedure setpalette; 
var i:integer; 
begin 
 for i:=0 to 127 do begin 
  {first 128 colors} 
  port[$3C8]:=i; {which mean that color i is set at port 3C8h} 
  port[$3C9]:=i div 2; {red value for color i} 
  port[$3C9]:=0; {green value} 
  port[$3C9]:=0; {blue value} 

  {next 128 colors (128..255)} 
  port[$3C8]:=128+i; 
  port[$3C9]:=63; 
  port[$3C9]:=i div 2; 
  port[$3C9]:=0; 
 end 
end; 

procedure codefire; 
begin 
 for w:=0 to 319 do vscreen[63680+w]:=random(2)*255; 
 for w:=320 to 63679 do 
  vscreen[w]:=(vscreen[w-320]+vscreen[w+319]+vscreen[w+320]+vscreen[w+321]) div 4; 
 {if you want a better effect, replace this procedure: 
  vscreen[64000-w]:=(vscreen[64000-w-320]+vscreen[64000-w+321]+ 
                     vscreen[64000-w+320]+vscreen[64000-w+319]) div 4;} 

 move(vscreen,mem[$A000:0],64000); 
end; 

BEGIN 
 setMCGA; 
 setpalette; 
 repeat 
  codefire; 
 until port[$60]=1; {until ESC is pressed} 
 setTEXT; 
end. 

{THE END}