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Plasma

KenshinHimura (Programmer)

(OP)

18 Nov 03 09:31

I'm trying to get a plasma graphic affect in qbasic. Does ne1 know how to do this?

CubeE101 (Programmer) · Answer 1 · 2003-11-18 12:27:06

Check Out My LudaTris Program at my site...

In the Projects or Qbasic section(s)...

Let me know if there are any areas you need help with...

I think I made a Plasma Sub for that program...

Also, for the basics & theory...
Check out the plasma tutorial at
www.flipcode.com/demomaking

Issue 4 is the plasma tutorial...
http://www.flipcode.com/demomaking/issue04.shtml

This is where I learned how to make plasma effects...

And, that is one of the best I have seen so far (until I make one

)

Have Fun, Be Young... Code BASIC
-Josh

http://cubee.topcities.com

KenshinHimura (Programmer) · Answer 2 · 2003-11-19 14:54:51

I sorta get how you do plasma. You use POINT and find the surounding colors and then average them or something like that. but what do you do after it looks plasma like. do u maniplulate the palette or something?

qbasicking (Programmer) · Answer 3 · 2003-11-19 15:45:19

goto www.qbasic.com > Files > gfx demos. There are two or three plasma demos there.

CubeE101 (Programmer) · Answer 4 · 2003-11-19 20:34:43

Yes, you manipulate the palette using SINs and COSs with the timer to give the palette an appearance of smooth rolling random colors...

From flipcode tutorial...

The c/c++ code is...
for (i=0; i<256; i++)
{
  vga->SetColour(
    i,
    (unsigned char)(32 + 31 * cos( i * PI / 128 + (double)currentTime/74 )),
    (unsigned char)(32 + 31 * sin( i * PI / 128 + (double)currentTime/63 )),
    (unsigned char)(32 - 31 * cos( i * PI / 128 + (double)currentTime/81 ))
  );
};

And the SetColour Function...
void VGA::SetColour( unsigned char i, unsigned char r, unsigned char g, unsigned char b )
{
// output the index of the colour
     outp( 0x3c8, i );
// and it's RGB components
     outp( 0x3c9, r );
     outp( 0x3c9, g );
     outp( 0x3c9, b );
};

Which produces this effect on the palette...

[Image from www.flipcode.com/demomaking]

To change this...

[Image from www.flipcode.com/demomaking]

Into this...

[Image from www.flipcode.com/demomaking]

The Basic Translation is:
For i = 0 to 255
' output the index of the colour
  OUT &H3C8, i
' and it's RGB components
  OUT &H3C9, Int(32 + 31 * Cos( i * PI / 128 + Timer))
  OUT &H3C9, Int(32 + 31 * Sin( i * PI / 128 + Timer))
  OUT &H3C9, Int(32 - 31 * Cos( i * PI / 128 + Timer))
Next

And don't forget to set PI = 3.1415...

How this Works is...
  Sin & Cos produce Waves, and At 0 and 360 degrees they connect, to make the ending the same as the begining...

[Image from www.flipcode.com/demomaking]

  there are 360 degrees in a circle...
  There are 2 * Pi radians in a circle...
  So to convert Degrees to radians we always say...
    R = D * (Pi * 2) / 360
  Or
    R = D * Pi / 180

  But we replace the degrees with Color, and there are only 256 Colors so, we use...
    R = C * (Pi * 2) / 256
  Or
    R = C * Pi / 128

  The Timer is used to offset the wave along the x-axis, to change the colors at a constant speed...

  The Cos & Sin functions will return values between -1 and 1
  So when you multiply that times 31 you get values between -31 and 31
  Then when you Add 32 to that, you get values between 0 and 63...
  Which is the range for the Red, Green, & Blue Values for the color palette...

To make the palette shift faster change Timer to Timer * Speed (2 is twice the speed)
Slower: Timer / Speed

If you need more help on this let me know...

For my LudaTris Game, I used this sub...
Sub FLIPPAL(Speed%)
  currentTime = Timer * Speed%
  For I% = 1 To 255
    CR = Int(32 + 31 * Cos(I% * PI / 128 + currentTime / 74))
    CG = Int(32 + 31 * Sin(I% * PI / 128 + currentTime / 63))
    CB = Int(32 - 31 * Cos(I% * PI / 128 + currentTime / 81))
    If GREY% Then
      CG = CR: CB = CR
    End If
    OUT &H3C8, I%
    OUT &H3C9, Int(CR)
    OUT &H3C9, Int(CG)
    OUT &H3C9, Int(CB)
  Next
End Sub

Have Fun, Be Young... Code BASIC
-Josh

http://cubee.topcities.com

KenshinHimura (Programmer) · Answer 5 · 2003-11-20 16:02:39

So this is how it goes.

draw random pixels on the screen
go through each pixel and find the surrounding colors
average those colors
redraw the averages colors on the screen
then manipulate the palette with the timer and triig functions so that its smooth palette changing

I just have 2 question about how you would make different clouds (like bigger or smaller)? And how would you average the points. I know with the point command but what would the formulas be like.

average = POINT(x, y) + POINT(x-1, y)+POINT(x+1,y)+etc...

until you get all the surrounding colors of that one pixel?

thx so much for your help so far.

CubeE101 (Programmer) · Answer 6 · 2003-11-20 20:33:05

No...
That is called smoothing / bluring...

but it is faster like this...
Def Seg = &HA000
For Y& = 1 to 198
  For X% = 1 to 318
    Offset& = Y& * 320 + X%
    C% = Peek(Offset&)
    CN% = Peek(Offset& - 320)
    CS% = Peek(Offset& + 320)
    CW% = Peek(Offset& - 1)
    CE% = Peek(Offset& + 1)
    Poke Offset&, (C% + CN% + CS% + CE% + CW%) \ 5
  Next
Next

--------------------------------
To Make it even Faster you can precalculate a division table...

255 (max color) * 5 (pixels to average) = 1275 (total possibilities)
Dim Div5(1275) As Integer
For I = 0 to 1275
  Div5(I) = I \ 5
Next

...

Def Seg = &HA000
For Y& = 1 to 198
  For X% = 1 to 318
    Offset& = Y& * 320 + X%
    C% = Peek(Offset&)
    C% = C% + Peek(Offset& - 320)
    C% = C% + Peek(Offset& + 320)
    C% = C% + Peek(Offset& - 1)
    C% = C% + Peek(Offset& + 1)
    Poke Offset&, Div5(C%)
  Next
Next
Def Seg

--------------------------------

As for the actual Plasma Effect...

Plasma 101
  By: Josh Stribling

The Random Pixel/Smooth is one method...

A more common way of creating a plasma effect is to use a mathmatical equation to describe the screen...
This is another area you can play around with Trig

Here is A snipplet from flipcode (again

)...
Function 1 is a sine function of the distance to the origin, and very commonly used for plasma equations:
  64 + 63 * (sin(hypot(200 - j, 320 - i) / 16)))

Function 2 is a product of my imagination:
  64 + 63 * sin(i / (37 + 15 * cos(j / 74))) * cos(j / (31 + 11 * sin(i / 57))))

You will notice that both functions are contained within the interval [0..127]. Also, when you make up your own functions, watch out for the divide by zero error

And The Basic Translation...
  *Note: I is X, J is Y  (I & J are commonly used in place of X & Y, especially when dealing with textures)

Breakdown of function 1...
These formulas Are designed for a 640 x 400 pixel buffer...
  Qbasic Can't Handle that, so...
    320 - j  -->  160 - X   Returns value between -159 and 160
    200 - i  -->  100 - Y   Returns value between -99 and 100

  hypot(x, y) returns the hypotenuse of the Right Triangle where:
    X = Adjacent
    Y = Opposite
  So...
    hypot = (X^2 + Y^2)^.5
  and in this case...
    ((160 - X)^2 + (100 - Y)^2)^.5
  this will return values between 0 and 187 which is the distance from the center of the screen

  You then divide this by the constant (the lower the number the more ripples it will produce, the higher... the less)
    since we are using 320 x 200 instead of 640 x 400, we will divide by 8 instead of 16...
    You can play with this value to get the desired effect
  So then you get a value between 0 and 23.375

  Now you get the Sin of that value, which sin will modulate it to 2 * Pi for you... (X Mod 2 * Pi)
    Mod returns the remainder of a divison operation... 5 / 2 = 2 r1, so 5 mod 2 = 1
    Sin(23.375) is the same as Sin(23.375 Mod 2* Pi)
    When the value reaches 2*pi, it will start over creating a continuous wave between -1 and 1...

  Now You multiply it by 63 to get a value between -63 and 63

  Last but Not least you add 64 to it to get a value between 1 and 127

  Which gives us this formula...

  64 + 63 * sin(((100 - x)^2 +(160 - y)^2)^.5 / 16))

  Now, as you can see this only returns a possible 128 values, and there are 256 color values

  So then you take the second function And it its result (which should be 0 to 127) to this to get a color value between 0 and 256

  It's that easy...

Breakdown of function 2...
  The second formula is a little more complicated, So if you want me to explain it in english also, let me know...
  Otherwise, I think I will save some time and give you the scaled and translated formula...

  For this one, you can use the original...
    64 + 63 * sin(x / (37 + 15 * cos(y / 74))) * cos(y / (31 + 11 * sin(x / 57))))
  Or
    64 + 63 * sin(x / (19 + 7 * cos(y / 37))) * cos(y / (15 + 5 * sin(x / 29))))
  Or you can play with the numbers how ever you like...

  In a nut Shell...

  Cos(y) & Sin(X) will both produce values between -1 and 1

  Sin(x * Cos(Y)) and Cos(Y * Sin(X)) will also = -1 to 1

  So, Guess What...
  Sin(X * Cos(Y)) * Cos(Y * Sin(X)) still = -1 to 1
  Since...
    1 * 1 & -1 * -1 both = 1
  and
    1 * -1 & -1 * 1 both = -1

  So you get basically the Same thing As before...
    64 + 63 * X
  where X = -1 to 1 which creates a value between 1 and 127

  So if you use this basic format (64 + 63 * X), you will always get a value between 0 and 127

  Now you add the 2 formulas
    Color = Formula1 + Formula2

  And draw the color to the screen
    Pset(X,Y),Color
  Or
    Def Seg = &hA000
    ...
      Poke Y * 320& + X, Color

The end result will look like this...

'*** Set the screen mode ***
Screen 13

'*** Set The Palette First

... Here is a grey scale Palette ***
For I% = 0 To 255
  OUT &H3C8, I%
  C% = I% \ 4
  OUT &H3C9, C%: OUT &H3C9, C%: OUT &H3C9, C%
Next

'*** Draw the plasma (this may take a while) ***
Def Seg = &HA000
For Y% = 0 to 199
  For X% = 0 to 319
    C1% = 64 + 63 * sin(((100 - x)^2 +(160 - y)^2)^.5 / 16))
    C2% = 64 + 63 * sin(x / (19 + 7 * cos(y / 37))) * cos(y / (15 + 5 * sin(x / 29))))
    Poke CLng(Y% * 320& + X%), C1% + C2%
  Next
Next

'*** Then loop through the Palette Cycle until a key is pressed***
K% = Inp(96)
Speed% = 2
Do
  currentTime = Timer * Speed%
  For I% = 1 To 255
    OUT &H3C8, I%
    OUT &H3C9, Int(32 + 31 * Cos(I% * PI / 128 + currentTime / 74))
    OUT &H3C9, Int(32 + 31 * Sin(I% * PI / 128 + currentTime / 63))
    OUT &H3C9, Int(32 - 31 * Cos(I% * PI / 128 + currentTime / 81))
  Next
Loop until Inp(96) <> K%

'*** Restore Palette and End ***
Palette
End

I hope this helps (my fingers are almost numb)
Have Fun Playing with Plasma (it's safer than fire),
-Josh

Have Fun, Be Young... Code BASIC
-Josh

http://cubee.topcities.com

KenshinHimura (Programmer) · Answer 7 · 2003-11-21 15:13:46

........man you typed out all that. no wonder your fingers are numb. Well seriosly I can't thank you enough for helpin me out. Those formulas are confusing, but I think I understand them. The only thing I'm pretty much confused about is using the TIMER in the equation to slow it down. I get how the TIMER changes at a constant rate but doesn't it return a really big number (if its not near after midnight). So how does making the TIMER # bigger make it faster. But at least I understand the SIN and COS better now. Thx a lot

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