- THE OUTLAW TRIAD DEMO-SERIES -

-------------------------- PART I ----------------------------------

                    Written by : Vulture/OT
                    Code in    : Pascal/Asm
                    Topic      : Fire effect

                

----------------------- Introduction -------------------------------

 Welcome to the Outlaw Triad demo-series! In these series we will be
 talking about programming demo-effects in either pascal or assembler.
 Theory behind the effects shall be discussed while a full sourcecode
 is also provided.
 These series are the sequals to the VGA-VUL# releases in which a few
 demo effects were handled and are meant for the beginner and
 intermediate coder.
 From now on all demo tutorials from Outlaw Triad will be released in
 these series. We from Outlaw Triad know there are already large
 amounts of demo trainers available (best of which seem to be the ones
 by Denthor/Asphyxia) but we experienced that it can be helpfull to
 read more than one document  on the same subject. Enjoy these series!

-------------------------- Theory ----------------------------------

 In this very first release I will cover a wellknown effect... FIRE!
 This is actually a simple routine, in theory. The only math is takes
 are some simple calculations to avarage certain values. Here we go:

 We will be using an unchained vgascreen with resolution 320*200*256.
 This will speed up our routine by a factor of 4 because we can plot
 4 pixels at a time due to vga-hardware. Now you need to setup a nice
 palette for use in our fire. E.g from dark red to bright yellow.

 Ok, we will also be using a 100 scanlines for our fire. This way, you
 will have another 100 scanlines left to do other things with.
 Create an array large enough to hold this data. We then flip the data
 to the vga. Why use an array? Because vga-memory is a lot slower than
 normal memory! In this case it is faster to update data in pc-memory
 and then flip it to the vga. This can also avoid flickering.
 Now, on the last row, put random values between 0 and 255 (or whatever
 colorrange you want. I used 0..85). Then create a fire effect like
 this:

 Start with the first pixel (actually 4 pixels) on the second row.
 Then take the 3 pixels above, the 3 pixels below and the 2 pixels
 besides that pixel. Divide by 3+3+2=8 to avarage these values. If the
 found value is not zero, decrease it by 1 to fade the fire to black.
 The fire on the bottom will then be brighter than the fire at the top
 which will make a good fire routine. Store the found value in the
 pixel ABOVE the current pixel. This will make the flames go up.
 Then point to the next pixel on the line and do the same. Do this for
 all lines. When finished, wait for a vertical retrace, flip the data
 to the vga screen and start over. That's it!
 In steps:

   - set bottom line with random values
   - start avaraging from second line
   - do all lines
   - wait for vertical retrace
   - flip to vga

 One thing left to say... As the bottom line is rather ugly with it's
 random values scattered on it, we hide the last few lines on the
 second page in display memory. Offscreen memory can be handy indeed!
 ;-)

 So you see, it's not that hard to understand. What can be hard is to
 realy code it. Take a look at the source to see how it can be done.
 The code here is in assembler because that is the real democode
 language to use, IMHO.
 There are many fire trainers available, so if you don't understand
 it, go study some more of them. Btw, thanks must go to all who have
 release fire code before I did (I learned from tutors too, you know
 ;-) ).

 Ok, this is all for now. Happy coding!

       - Vulture / Outlaw Triad

------------------------ Distro Sites ------------------------------

 Call our distros to get all our releases.

  BlueNose    World HQ     +31 (0)345-619401
  FireHouse   Distrosite   +31 (0)528-274176      More distros wanted!
  The Force   Distrosite   +31 (0)36-5346967
  MagicWare   Italian HQ   +39  6-52355532

--------------------------- Contact --------------------------------

 Want to contact Outlaw Triad for some reason? You can reach us at our
 distrosites in Holland. Or if you have e-mail access, mail us:

   Vulture  (coder/pr)     comma400@tem.nhl.nl

 Our internet homepage:

   httm://www.tem.nhl.nl/~comma400/vulture.html

 These internet adresses should be valid at least till june 1996.

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