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# Fire and explosion

Posted on 2001-07-15
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Where I can find the good explosion and fire algorithm. I have seen in games that when an object is destroyed. An irregular shape is drawn there. And the color of shape darkens from the border to inside gradually. And this gives the effect of fire. What is the technique behind it. (Is there any supporting thing in dx 8).
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Question by:Sana060101

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Expert Comment

ID: 6284580
It's a particle system, usually.  Image a whole bunch of small quads moving (exploding) away from the point of the explosion.  They are usually done by texturing the quads with an appropriate texture and alpha blending them.  As they move away from the point of the explosion you will want the alpha value to increase (the transparency) and maybe the color (from red to grey or black).  When you have a lot of them moving outward in every direction, it will look like an explosion.
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Expert Comment

ID: 6287827
You  could  break  your  object down to a triangle list,
then copy the list to another list reversing the normals
so you could draw both sides of the triangles.

Then you could give each triangle a random vector outward, and a random rotation.  For each frame,  you  rotate  and expand.  Do  these calculations from a reference triangle list that you use over again so you can calculate rotation, and offset.

I did something like this on an old 386 computer programming in DOS. It looked pretty cool, but then again you really don't expect alot from a 386.
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Expert Comment

ID: 6288056
Another suggestion ... I have a couple of gif's with fire and explosion fx. These are typicaly 20 frames in duration. What I then did was convert each frame to a .dds texture map (.dds is a 4 channel texture map with alpha, red, green and blue) Then place a simple square polygon at the position in space where I want the explosion to occur and then 'playback' the 20 frames ... and u have a photorealistic explosion effect. In fact, all the pyrotec fx are .dds texture maps 'projected' onto a polygon at the location that I want it to occur. Minimal processing overhead and great fx.
If u want a sample gif to try out, Have a look at http://www.cybermike.co.za/clanibh00.htm  ... you are quite welcome to copy and play around with the artwork. If this is the way u want to go, let me know ... I have some more. You really dont want to tie up your cpu calculating fire and smoke.
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Author Comment

ID: 6288383
Cybermike
I liked the way you have created fire. But I have never used fx. Can you send me a simple application  that implements the technique.
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Accepted Solution

cybermike3d earned 200 total points
ID: 6291908
The following code snippets do all the work

First, load the polygon with its texture map sequence.
'---------------------------------------
l1 = 30: i = 0:   meshn\$(l1, i) = "poly05.x":   strtexname(l1, i) = "smoke01.dds": loadmeshtex:    meshno(930) = 30
l1 = 30: i = 1:   meshn\$(l1, i) = "poly05.x":   strtexname(l1, i) = "smoke01.dds": loadmeshtex:    meshno(930) = 30
l1 = 30: i = 2:   meshn\$(l1, i) = "poly05.x":   strtexname(l1, i) = "smoke02.dds": loadmeshtex:    meshno(930) = 30
l1 = 30: i = 3:   meshn\$(l1, i) = "poly05.x":   strtexname(l1, i) = "smoke03.dds": loadmeshtex:    meshno(930) = 30
l1 = 30: i = 4:   meshn\$(l1, i) = "poly05.x":   strtexname(l1, i) = "smoke04.dds": loadmeshtex:    meshno(930) = 30
l1 = 30: i = 5:   meshn\$(l1, i) = "poly05.x":   strtexname(l1, i) = "smoke05.dds": loadmeshtex:    meshno(930) = 30
l1 = 30: i = 6:   meshn\$(l1, i) = "poly05.x":   strtexname(l1, i) = "smoke06.dds": loadmeshtex:    meshno(930) = 30
l1 = 30: i = 7:   meshn\$(l1, i) = "poly05.x":   strtexname(l1, i) = "smoke07.dds": loadmeshtex:    meshno(930) = 30
l1 = 30: i = 8:   meshn\$(l1, i) = "poly05.x":   strtexname(l1, i) = "smoke08.dds": loadmeshtex:    meshno(930) = 30
l1 = 30: i = 9:   meshn\$(l1, i) = "poly05.x":   strtexname(l1, i) = "smoke09.dds": loadmeshtex:    meshno(930) = 30
l1 = 30: i = 10:  meshn\$(l1, i) = "poly05.x":   strtexname(l1, i) = "smoke10.dds": loadmeshtex:    meshno(930) = 30
l1 = 30: i = 11:  meshn\$(l1, i) = "poly05.x":   strtexname(l1, i) = "smoke11.dds": loadmeshtex:    meshno(930) = 30
l1 = 30: i = 12:  meshn\$(l1, i) = "poly05.x":   strtexname(l1, i) = "smoke12.dds": loadmeshtex:    meshno(930) = 30
l1 = 30: i = 13:  meshn\$(l1, i) = "poly05.x":   strtexname(l1, i) = "smoke13.dds": loadmeshtex:    meshno(930) = 30
l1 = 30: i = 14:  meshn\$(l1, i) = "poly05.x":   strtexname(l1, i) = "smoke14.dds": loadmeshtex:    meshno(930) = 30
l1 = 30: i = 15:  meshn\$(l1, i) = "poly05.x":   strtexname(l1, i) = "smoke15.dds": loadmeshtex:    meshno(930) = 30
l1 = 30: i = 16:  meshn\$(l1, i) = "poly05.x":   strtexname(l1, i) = "smoke16.dds": loadmeshtex:    meshno(930) = 30
l1 = 30: i = 17:  meshn\$(l1, i) = "poly05.x":   strtexname(l1, i) = "smoke17.dds": loadmeshtex:    meshno(930) = 30
l1 = 30: i = 18:  meshn\$(l1, i) = "poly05.x":   strtexname(l1, i) = "smoke18.dds": loadmeshtex:    meshno(930) = 30
l1 = 30: i = 19:  meshn\$(l1, i) = "poly05.x":   strtexname(l1, i) = "smoke19.dds": loadmeshtex:    meshno(930) = 30
l1 = 30: i = 20:  meshn\$(l1, i) = "poly05.x":   strtexname(l1, i) = "smoke20.dds": loadmeshtex:    meshno(930) = 30
'--------------------------------------
Set g_mesh(l1, i) = g_D3DX.LoadMeshFromX(rootdir\$ + "\" + meshn\$(l1, i), _
D3DXMESH_MANAGED, _
g_D3DDevice, _
Nothing, _
MtrlBuffer, _
g_NumMaterials)
g_D3DX.BufferGetMaterial MtrlBuffer, 0, g_meshmaterials(l1, i)
If strtexname(l1, i) = "" Then strtexname(l1, i) = g_D3DX.BufferGetTextureName(MtrlBuffer, 0)
If strtexname(l1, i) <> "" Then
Set g_meshtextures(l1, i) = g_D3DX.CreateTextureFromFile(g_D3DDevice, rootdir\$ + "\" + strtexname(l1, i))
End If
End Sub
'-----------------------------------------------
'then draw the billowing smoke and flame trail behind the craft
'----------------------------------------------
'To save space, I use the same holding variable for the bullets as the smoke ... if craft is going down in flames ... it aint shooting bullets

'----------------------------------------------------------- draw smoke
'Draw fire & smoke on friendlies (Reddish tint)
For l = startoffriend To endoffriend
If bullets(l, 1) = 1 Then
' In order to prevent tiling, one has to draw the smoke from the furthest to the closest.
' so u have to determine if the craft is comming towards or going away from u
ixdif = eye.X - posx(l): iydif = eye.z - posz(l): getcord: angl1 = itnang - heading(l): angl1 = Int(angl1): angl3 = itnang
If angl1 > 180 Then angl1 = angl1 - 360
If angl1 < -180 Then angl1 = angl1 + 360
If itnang > 180 Then itnang = itnang - 360
ixdif = eye.X - posx(sel)
iydif = eye.z - posz(sel)
getcord
angl2 = Abs(Int(itnang - angl3))
If angl2 > 180 Then angl2 = angl2 - 360
If angl2 < -180 Then angl2 = angl2 + 360
'if craft is outside the field of vission ... dont draw the smoke
If angl2 < 35 Then
If angl1 < 90 And angl1 > -90 Then
For l2 = 2 To 20
i = l2
l1 = meshno(930)
l5 = meshno(930)
scalez = 0.02 * l2
g_meshmaterials(l1, i).emissive.r = 0.6: g_meshmaterials(l1, i).emissive.g = 0: g_meshmaterials(l1, i).emissive.b = 0
light.Ambient.r = 1: light.Ambient.g = 1: light.Ambient.b = 1
g_D3DDevice.SetRenderState D3DRS_AMBIENT, &HFFFFFF
D3DXMatrixMultiply matWorld, matWorld, rotMatrix
smokeno = Int(Rnd(1) * 16) + 1
D3DXMatrixTranslation transMatrix, bulletx(l, l2), bullety(l, l2), bulletz(l, l2)
D3DXMatrixScaling scaleMatrix, scalez, scalez, scalez
D3DXMatrixMultiply matWorld, scaleMatrix, rotMatrix
D3DXMatrixMultiply matWorld, matWorld, transMatrix
g_D3DDevice.SetTransform D3DTS_WORLD, matWorld
g_D3DDevice.SetMaterial g_meshmaterials(l5, l2)
g_D3DDevice.SetTexture 0, g_meshtextures(l5, smokeno)
g_mesh(l5, l2).DrawSubset 0
Next
End If

If angl1 > 90 Or angl1 < -90 Then
For l2 = 20 To 2 Step -1
i = l2
l1 = meshno(930)
l5 = meshno(930)
scalez = 0.02 * l2
g_meshmaterials(l1, i).emissive.r = 0.3: g_meshmaterials(l1, i).emissive.g = 0: g_meshmaterials(l1, i).emissive.b = 0
light.Ambient.r = 1: light.Ambient.g = 1: light.Ambient.b = 1
g_D3DDevice.SetRenderState D3DRS_AMBIENT, &HFFFFFF
D3DXMatrixMultiply matWorld, matWorld, rotMatrix
smokeno = Int(Rnd(1) * 16) + 1
D3DXMatrixTranslation transMatrix, bulletx(l, l2), bullety(l, l2), bulletz(l, l2)
D3DXMatrixScaling scaleMatrix, scalez, scalez, scalez
D3DXMatrixMultiply matWorld, scaleMatrix, rotMatrix
D3DXMatrixMultiply matWorld, matWorld, transMatrix
g_D3DDevice.SetTransform D3DTS_WORLD, matWorld
g_D3DDevice.SetMaterial g_meshmaterials(l5, l2)
g_D3DDevice.SetTexture 0, g_meshtextures(l5, smokeno)
g_mesh(l5, l2).DrawSubset 0
Next
End If
End If
End If
Next

'-------------------------------------------------------
' getcord is the math behind the 3d angular translation
'-------------------------------------------------------
Sub getcord()
itargetrange = Sqr(ixdif ^ 2 + iydif ^ 2)
If iydif <> 0 Then itgan = Atn(ixdif / iydif) * 57.2958
If iydif = 0 And ixdif = 0 Then itgan = 0: itgang = 0
If iydif = 0 And ixdif < 0 Then itgan = 270
If iydif = 0 And ixdif > 0 Then itgan = 90
itgang = itgan
If iydif < 0 Then itgang = 180 + itgan
If ixdif < 0 And iydif > 0 Then itgang = 360 + itgan
itnang = ina + itgang
If itnang > 360 Then itnang = itnang - 360
If itnang < 0 Then itnang = itnang + 360
End Sub

So there you go, make a few bitmaps of flame and sparks and smoke, and play them in quick sucsession on a polygon. Its like having a big alpha blended screen in space and u can playback any movie clip u like. Use the artwork of the gif on the link i gave u above ...

One of these days im gonna figure out how to channel an avi into a texture map ... and then im really gonna have some fun ...

regards
(yberMike ;-D)

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LVL 2

Expert Comment

ID: 6292894
I've been thinking of doing that myself... converting movies into "sprite" type textures.  You could do some cool stuff... you could even simulate a big "Downtown New York style" screen with ads for stuff running in the scene somewhere.
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