OpenGL & Fog

Post by **Polo** » Thu Jun 30, 2005 7:10 pm

Hi !
I've troubles using Fog with Opengl...
I'm setting all up like in Nehe's tutorials, but unfortunately the fog doesn't show up...
BTW, I'm wondering, how do OpenGL know where the fog need to start and to end ? How can it know the camera position ?

traumatic · Post by **traumatic** » Thu Jun 30, 2005 9:07 pm

What's your exact problem?

If your code looks something like the following, it should work.

Code: Select all

glFogi_(#GL_FOG_MODE, #GL_LINEAR)
glFogf_(#GL_FOG_START, 0.0)
glFogf_(#GL_FOG_END, 7.0)
glEnable_(#GL_FOG)

Polo wrote:BTW, I'm wondering, how do OpenGL know where the fog need to start and to end ? How can it know the camera position ?

Well, it doesn't. OpenGL fog is just blending, no magic involved.

BTW, even if it's not necessary in order to make fogging work, of course
OpenGL keeps track of all matrices. How else would e.g. glRotatef_() work
at all?

DarkDragon · Post by **DarkDragon** » Fri Jul 01, 2005 8:23 am

Are we talking about normal fog with no extension or are we talking about the volumetric fog?

Post by **Polo** » Fri Jul 01, 2005 9:23 am

Well, normal fog.
My code is like Traumatic's, but unfortunately I got a... strange result

http://gtnsoft.free.fr/fogtest.jpg

Hum... Well....
I must do something wrong somewhere...

Code: Select all

c=AllocateMemory(16)
PokeF(c,0.5)
PokeF(c+4,0.5)
PokeF(c+8,0.5)
PokeF(c+12,0.5)
glFogfv_(#GL_FOG_COLOR, c)
FreeMemory(c)

glFogi_(#GL_FOG_MODE, #GL_EXP)
glFogf_(#GL_FOG_START, 0.0);;
glFogf_(#GL_FOG_END, 7.0)
glEnable_(#GL_FOG)

I've put a color, without the color it looks the same, but the things you see grey are black...

DarkDragon · Post by **DarkDragon** » Fri Jul 01, 2005 10:02 am

Polo wrote:Well, normal fog.
My code is like Traumatic's, but unfortunately I got a... strange result
http://gtnsoft.free.fr/fogtest.jpg

Yes, it's right the picture shows the fog right yeah, like here too.
Use volumetric fog and you get results like that what you want:

Code: Select all

XIncludeFile "C:\Dokumente und Einstellungen\Daniel\Eigene Dateien\Eigene Programme\GL\GL.pbi"

#WindowWidth = 500
#WindowHeight = 400
#WindowFlags = #PB_Window_TitleBar | #PB_Window_MaximizeGadget | #PB_Window_SystemMenu | #PB_Window_MinimizeGadget | #PB_Window_ScreenCentered
Version.f = 1.0

#GL_FOG_COORDINATE_SOURCE_EXT = $8450
#GL_FOG_COORDINATE_EXT = $8451

Global hWnd.l, Event

Procedure MyWindowCallback(WindowID, Message, wParam, lParam)
  Result = #PB_ProcessPureBasicEvents
  If Message = #WM_SIZE
    glViewport_(0, 0, WindowWidth(), WindowHeight())
    Result = 1
  EndIf
  ProcedureReturn Result
EndProcedure

Procedure InitExtension()
  Shared glFogCoordfEXT
  If FindString(PeekS(glGetString_(#GL_EXTENSIONS)), "GL_EXT_fog_coord", 0) > 0
    glFogCoordfEXT = wglGetProcAddress_("glFogCoordfEXT")
    ProcedureReturn 1
  Else
    ProcedureReturn 0
  EndIf
EndProcedure

Procedure glFogCoordf_(Val.f)
  Shared glFogCoordfEXT
  ProcedureReturn CallFunctionFast(glFogCoordfEXT, Val.f)
EndProcedure

Procedure SetCamera(FOV.f, X.f, Y.f, Z.f, AngleX.f, AngleY.f, AngleZ.f, Near.f, Far.f) ;Sets the cameraposition and the FOV
  glMatrixMode_(5889)
  glLoadIdentity_()
  gluPerspective__(FOV, WindowWidth()/WindowHeight(), Near.f, Far.f)
  glRotatef_(AngleX, 1.0, 0.0, 0.0)
  glRotatef_(AngleY, 0.0, 1.0, 0.0)
  glRotatef_(AngleZ, 0.0, 0.0, 1.0)
  glTranslatef_(X, Y, Z)
  glMatrixMode_(5888)
  
  glDepthRange__(Near.f, Far.f)
EndProcedure

Procedure LoadTexture_(Filename.s, TexFilter.l) ; Returns the texture for an OpenGL application
  img = LoadImage(#PB_Any, Filename.s)
  Width.l=ImageWidth() 
  Height.l=ImageHeight()  
  Size.l=Width * Height
  
  Dim ImageData.b(Size*3)
  
  StartDrawing(ImageOutput())
  For Y=0 To Height-1
    For X=0 To Width-1
     
      Color = Point(X,Y)
      ImageData(i)=Red(Color)
      i+1
      ImageData(i)=Green(Color)
      i+1
      ImageData(i)=Blue(Color)
      i+1
    
    Next
  Next
  StopDrawing()
  
  glGenTextures_(1, @Tex) ;Textur speichern
  If TexFilter = 0 ;versch. Textur-Filter
    glBindTexture_($0DE1, Tex)
    glTexParameteri_($0DE1, $2800, $2600)
    glTexParameteri_($0DE1, $2801, $2600)
    glTexImage2D_($0DE1, 0, 6407, Width, Height, 0, 6407, $1401, @ImageData()) 
  ElseIf TexFilter = 1
    glBindTexture_($0DE1, Tex)
    glTexParameteri_($0DE1, $2800, $2601)
    glTexParameteri_($0DE1, $2801, $2601)
    glTexImage2D_($0DE1, 0, 6407, Width, Height, 0, 6407, $1401, @ImageData())
  ElseIf TexFilter = 2
    glBindTexture_($0DE1, Tex)
    glTexParameteri_($0DE1, $2800, $2601)
    glTexParameteri_($0DE1, $2801, $2701)
    gluBuild2DMipmaps_($0DE1, 3, Width, Height, 6407, $1401, @ImageData())
  EndIf
  FreeImage(img)
  ProcedureReturn Tex
EndProcedure

Procedure DrawObject(Steps, Stacks)
  Shared X.f, Y.f, Z.f
  X.f = X * -1
  Y.f = Y * -1
  Z.f = Z * -1
  
  glBegin_(#GL_TRIANGLES)
  a.f : b.f
  While a <= #PI*2
   b = 0
   While b <= #PI*2
    mx.f = Sin(b)*Cos(a)
    my.f = Sin(a)
    mz.f = Cos(b)*Cos(a)
    glFogCoordf_(Sqr(Pow(X-mx, 2)+Pow(Y-my, 2)+Pow(Z-mz, 2)))
    glVertex3f_(mx, my, mz)
    
    mx.f = Sin(b)*Cos(a + (#PI*2)/Steps)
    my.f = Sin(a + (#PI*2)/Steps)
    mz.f = Cos(b)*Cos(a + (#PI*2)/Steps)
    glFogCoordf_(Sqr(Pow(X-mx, 2)+Pow(Y-my, 2)+Pow(Z-mz, 2)))
    glVertex3f_(mx, my, mz)
    
    mx.f = Sin(b + (#PI*2)/Stacks)*Cos(a + (#PI*2)/Steps)
    my.f = Sin(a + (#PI*2)/Steps )
    mz.f = Cos(b + (#PI*2)/Stacks)*Cos(a + (#PI*2)/Steps)
    glFogCoordf_(Sqr(Pow(X-mx, 2)+Pow(Y-my, 2)+Pow(Z-mz, 2)))
    glVertex3f_(mx, my, mz)
    
    mx.f = Sin(b + (#PI*2)/Stacks)*Cos(a + (#PI*2)/Steps)
    my.f = Sin(a + (#PI*2)/Steps )
    mz.f = Cos(b + (#PI*2)/Stacks)*Cos(a + (#PI*2)/Steps)
    glFogCoordf_(Sqr(Pow(X-mx, 2)+Pow(Y-my, 2)+Pow(Z-mz, 2)))
    glVertex3f_(mx, my, mz)
    
    mx.f = Sin(b + (#PI*2)/Stacks)*Cos(a)
    my.f = Sin(a)
    mz.f = Cos(b + (#PI*2)/Stacks)*Cos(a)
    glFogCoordf_(Sqr(Pow(X-mx, 2)+Pow(Y-my, 2)+Pow(Z-mz, 2)))
    glVertex3f_(mx, my, mz)
    
    mx.f = Sin(b)*Cos(a)
    my.f = Sin(a)
    mz.f = Cos(b)*Cos(a)
    glFogCoordf_(Sqr(Pow(X-mx, 2)+Pow(Y-my, 2)+Pow(Z-mz, 2)))
    glVertex3f_(mx, my, mz)
    
    
    b + (#PI*2)/Stacks
   Wend
   a + (#PI*2)/Steps
  Wend
  glEnd_()
  
  X.f = X * -1
  Y.f = Y * -1
  Z.f = Z * -1
EndProcedure

If OpenWindow(0, 0, 0, #WindowWidth, #WindowHeight, #WindowFlags, "OpenGL Scene "+StrF(Version, 1))

SetWindowCallback(@MyWindowCallback())

hWnd = WindowID(0)
hDC = GetDC_(hWnd)

;Initialize OpenGL
pfd.PIXELFORMATDESCRIPTOR
pfd\nSize        = SizeOf(PIXELFORMATDESCRIPTOR)
pfd\nVersion     = 1
pfd\dwFlags      = #PFD_SUPPORT_OPENGL | #PFD_DOUBLEBUFFER | #PFD_DRAW_TO_WINDOW
pfd\iLayerType   = #PFD_MAIN_PLANE
pfd\iPixelType   = #PFD_TYPE_RGBA
pfd\cColorBits   = 24
pfd\cDepthBits   = 32
Pixformat = ChoosePixelFormat_(hDC, pfd)
SetPixelFormat_(hDC, Pixformat, pfd)
hrc = wglCreateContext_(hDC)
wglMakeCurrent_(hDC, hrc)

SwapBuffers_(hDC)
glEnable_(#GL_DEPTH_TEST)

If InitExtension()

Dim fogColor.f(3)
fogColor(0) = 0.25
fogColor(1) = 0.25
fogColor(2) = 0.25
fogColor(3) = 1.0

glEnable_(#GL_FOG)
glFogi_(#GL_FOG_MODE, #GL_LINEAR)
glFogfv_(#GL_FOG_COLOR, @fogColor())
glFogf_(#GL_FOG_START ,  -0.5)
glFogf_(#GL_FOG_END   ,  7.5)
glHint_(#GL_FOG_HINT  , #GL_NICEST)
glFogi_(#GL_FOG_COORDINATE_SOURCE_EXT, #GL_FOG_COORDINATE_EXT)

glClearColor_(fogColor(0), fogColor(1), fogColor(2), fogColor(3))

; glPolygonMode_(#GL_FRONT_AND_BACK, #GL_LINE) ;Just wireframe mode

AngleX.f
AngleY.f
AngleZ.f
X.f
Y.f
Z.f = -5.0

Repeat
  Rot.f + 0.5
  glClear_(#GL_COLOR_BUFFER_BIT | #GL_DEPTH_BUFFER_BIT)
  SetCamera(45.0, X, Y, Z, AngleX, AngleY, AngleZ, 0.1, 50.0)
  glLoadIdentity_()
  DrawObject(20, 20)
  SwapBuffers_(hDC)
  
  
  If GetAsyncKeyState_(#VK_UP)
    Z + Cos(AngleX/180*#PI)*Cos(AngleY/180*#PI)*0.04
    Y + Sin(AngleX/180*#PI)*0.04
    X - Sin(AngleY/180*#PI)*Cos(AngleX/180*#PI)*0.04
  ElseIf GetAsyncKeyState_(#VK_DOWN)
    Z - Cos(AngleX/180*#PI)*Cos(AngleY/180*#PI)*0.04
    Y - Sin(AngleX/180*#PI)*0.04
    X + Sin(AngleY/180*#PI)*Cos(AngleX/180*#PI)*0.04
  EndIf
  
  If GetAsyncKeyState_(#VK_LEFT)
    AngleY - 0.5
  ElseIf GetAsyncKeyState_(#VK_RIGHT)
    AngleY + 0.5
  EndIf
  If GetAsyncKeyState_(#VK_PRIOR)
    AngleX - 0.5
  ElseIf GetAsyncKeyState_(#VK_NEXT)
    AngleX + 0.5
  EndIf
  
  
  Event = WindowEvent()
Until Event = #PB_Event_CloseWindow
EndIf
ReleaseDC_(hWnd, hDC)
EndIf
End

Post by **Polo** » Fri Jul 01, 2005 10:11 am

Hi !
Thanks for your code, it seems it does what I want, but...
You seem to call the extension glFogCoordf with glVertex3f... It's unusable, since calling glVertex is really slow !
But it seems that with the traumatic's code it should work :
http://nehe.gamedev.net/data/lessons/le ... ?lesson=16
On this nehe tutorial, it's what I'm trying to do... I don't understand why it works for them and not for me..

DarkDragon · Post by **DarkDragon** » Fri Jul 01, 2005 11:41 am

Ok, I have translated a part from the NeHe tutorial:

Code: Select all

XIncludeFile "C:\Dokumente und Einstellungen\Daniel\Eigene Dateien\Eigene Programme\GL\GL.pbi"

#WindowWidth = 500
#WindowHeight = 400
#WindowFlags = #PB_Window_TitleBar | #PB_Window_MaximizeGadget | #PB_Window_SystemMenu | #PB_Window_MinimizeGadget | #PB_Window_ScreenCentered
Version.f = 1.0

Global hWnd.l, Event

Procedure MyWindowCallback(WindowID, Message, wParam, lParam)
  Result = #PB_ProcessPureBasicEvents
  If Message = #WM_SIZE
    glViewport_(0, 0, WindowWidth(), WindowHeight())
    Result = 1
  EndIf
  ProcedureReturn Result
EndProcedure

Procedure SetCamera(FOV.f, Near.f, Far.f)
  glMatrixMode_(#GL_PROJECTION)
  glLoadIdentity_()
  gluPerspective__(FOV, WindowWidth()/WindowHeight(), Near.f, Far.f)
  glMatrixMode_(#GL_MODELVIEW)
  
  ;glDepthRange__(Near.f, Far.f)
EndProcedure

Procedure LoadTexture_(Filename.s, TexFilter.l) ; Returns the texture for an OpenGL application
  img = LoadImage(#PB_Any, Filename.s)
  Width.l=ImageWidth() 
  Height.l=ImageHeight()  
  Size.l=Width * Height
  
  Dim ImageData.b(Size*3)
  
  StartDrawing(ImageOutput())
  For Y=0 To Height-1
    For X=0 To Width-1
     
      Color = Point(X,Y)
      ImageData(i)=Red(Color)
      i+1
      ImageData(i)=Green(Color)
      i+1
      ImageData(i)=Blue(Color)
      i+1
    
    Next
  Next
  StopDrawing()
  
  glGenTextures_(1, @Tex) ;Textur speichern
  If TexFilter = 0 ;versch. Textur-Filter
    glBindTexture_($0DE1, Tex)
    glTexParameteri_($0DE1, $2800, $2600)
    glTexParameteri_($0DE1, $2801, $2600)
    glTexImage2D_($0DE1, 0, 6407, Width, Height, 0, 6407, $1401, @ImageData()) 
  ElseIf TexFilter = 1
    glBindTexture_($0DE1, Tex)
    glTexParameteri_($0DE1, $2800, $2601)
    glTexParameteri_($0DE1, $2801, $2601)
    glTexImage2D_($0DE1, 0, 6407, Width, Height, 0, 6407, $1401, @ImageData())
  ElseIf TexFilter = 2
    glBindTexture_($0DE1, Tex)
    glTexParameteri_($0DE1, $2800, $2601)
    glTexParameteri_($0DE1, $2801, $2701)
    gluBuild2DMipmaps_($0DE1, 3, Width, Height, 6407, $1401, @ImageData())
  EndIf
  FreeImage(img)
  ProcedureReturn Tex
EndProcedure

Procedure DrawCube()
    glBegin_(#GL_QUADS)
        ;' Front Face
        glNormal3f_( 0.0, 0.0, 1.0 )
        glTexCoord2f_( 0.0, 0.0 ) : glVertex3f_( -1.0,-1.0, 1.0 )
        glTexCoord2f_( 1.0, 0.0 ) : glVertex3f_(  1.0,-1.0, 1.0 )
        glTexCoord2f_( 1.0, 1.0 ) : glVertex3f_(  1.0, 1.0, 1.0 )
        glTexCoord2f_( 0.0, 1.0 ) : glVertex3f_( -1.0, 1.0, 1.0 )
        ;' Back Face
        glNormal3f_( 0.0, 0.0,-1.0 )
        glTexCoord2f_( 1.0, 0.0 ) : glVertex3f_( -1.0,-1.0,-1.0 )
        glTexCoord2f_( 1.0, 1.0 ) : glVertex3f_( -1.0, 1.0,-1.0 )
        glTexCoord2f_( 0.0, 1.0 ) : glVertex3f_(  1.0, 1.0,-1.0 )
        glTexCoord2f_( 0.0, 0.0 ) : glVertex3f_(  1.0,-1.0,-1.0 )
        ;' Top Face
        glNormal3f_( 0.0, 1.0, 0.0 )
        glTexCoord2f_( 0.0, 1.0 ) : glVertex3f_( -1.0, 1.0,-1.0 )
        glTexCoord2f_( 0.0, 0.0 ) : glVertex3f_( -1.0, 1.0, 1.0 )
        glTexCoord2f_( 1.0, 0.0 ) : glVertex3f_(  1.0, 1.0, 1.0 )
        glTexCoord2f_( 1.0, 1.0 ) : glVertex3f_(  1.0, 1.0,-1.0 )
        ;' Bottom Face
        glNormal3f_( 0.0,-1.0, 0.0 )
        glTexCoord2f_( 1.0, 1.0 ) : glVertex3f_( -1.0,-1.0,-1.0 )
        glTexCoord2f_( 0.0, 1.0 ) : glVertex3f_(  1.0,-1.0,-1.0 )
        glTexCoord2f_( 0.0, 0.0 ) : glVertex3f_(  1.0,-1.0, 1.0 )
        glTexCoord2f_( 1.0, 0.0 ) : glVertex3f_( -1.0,-1.0, 1.0 )
        ;' Right Face
        glNormal3f_( 1.0, 0.0, 0.0 )
        glTexCoord2f_( 1.0, 0.0 ) : glVertex3f_(  1.0,-1.0,-1.0 )
        glTexCoord2f_( 1.0, 1.0 ) : glVertex3f_(  1.0, 1.0,-1.0 )
        glTexCoord2f_( 0.0, 1.0 ) : glVertex3f_(  1.0, 1.0, 1.0 )
        glTexCoord2f_( 0.0, 0.0 ) : glVertex3f_(  1.0,-1.0, 1.0 )
        ;' Left Face
        glNormal3f_(-1.0, 0.0, 0.0 )
        glTexCoord2f_( 0.0, 0.0 ) : glVertex3f_( -1.0,-1.0,-1.0 )
        glTexCoord2f_( 1.0, 0.0 ) : glVertex3f_( -1.0,-1.0, 1.0 )
        glTexCoord2f_( 1.0, 1.0 ) : glVertex3f_( -1.0, 1.0, 1.0 )
        glTexCoord2f_( 0.0, 1.0 ) : glVertex3f_( -1.0, 1.0,-1.0 )
    glEnd_()
EndProcedure

If OpenWindow(0, 0, 0, #WindowWidth, #WindowHeight, #WindowFlags, "OpenGL Scene "+StrF(Version, 1))

SetWindowCallback(@MyWindowCallback())

hWnd = WindowID(0)
hDC = GetDC_(hWnd)

;Initialize OpenGL
pfd.PIXELFORMATDESCRIPTOR
pfd\nSize        = SizeOf(PIXELFORMATDESCRIPTOR)
pfd\nVersion     = 1
pfd\dwFlags      = #PFD_SUPPORT_OPENGL | #PFD_DOUBLEBUFFER | #PFD_DRAW_TO_WINDOW
pfd\iLayerType   = #PFD_MAIN_PLANE
pfd\iPixelType   = #PFD_TYPE_RGBA
pfd\cColorBits   = 24
pfd\cDepthBits   = 32
pixformat = ChoosePixelFormat_(hDC, pfd)
SetPixelFormat_(hDC, pixformat, pfd)
hrc = wglCreateContext_(hDC)
wglMakeCurrent_(hDC, hrc)

Dim LightAmbient.f(3)
For k=0 To 2
LightAmbient(k) = 0.5
Next
LightAmbient(1) = 1.0
Dim LightDiffuse.f(3)
For k=0 To 3
LightDiffuse(k) = 1.0
Next
Dim LightPosition.f(3)
LightPosition(2) = 2.0
LightPosition(3) = 1.0
Dim fogMode.l(2)
fogMode(0) = #GL_EXP
fogMode(1) = #GL_EXP2
fogMode(2) = #GL_LINEAR
Dim fogColor.f(4)
For k=0 To 2
fogColor(k) = 0.5
Next
fogColor(3) = 1.0

fogfilter = 2

glEnable_(#GL_LIGHTING)

glEnable_(#GL_TEXTURE_2D);							// Enable Texture Mapping
glShadeModel_(#GL_SMOOTH);							// Enable Smooth Shading
glClearColor_(fogColor(0),fogColor(1),fogColor(2),fogColor(3));					// We'll Clear To The Color Of The Fog
glClearDepth__(1.0);									// Depth Buffer Setup
glEnable_(#GL_DEPTH_TEST);							// Enables Depth Testing
glDepthFunc_(#GL_LEQUAL);								// The Type Of Depth Testing To Do
glHint_(#GL_PERSPECTIVE_CORRECTION_HINT, #GL_NICEST);	// Really Nice Perspective Calculations
glLightfv_(#GL_LIGHT1, #GL_AMBIENT, @LightAmbient());		// Setup The Ambient Light
glLightfv_(#GL_LIGHT1, #GL_DIFFUSE, @LightDiffuse());		// Setup The Diffuse Light
glLightfv_(#GL_LIGHT1, #GL_POSITION,@LightPosition());	// Position The Light
glEnable_(#GL_LIGHT1);								// Enable Light One
glFogi_(#GL_FOG_MODE, fogMode(fogfilter));			// Fog Mode
glFogfv_(#GL_FOG_COLOR, @fogColor());					// Set Fog Color
glFogf_(#GL_FOG_DENSITY, 0.35);						// How Dense Will The Fog Be
glHint_(#GL_FOG_HINT, #GL_NICEST);					// Fog Hint Value
glFogf_(#GL_FOG_START, 1.0);							// Fog Start Depth
glFogf_(#GL_FOG_END, 5.0);							// Fog End Depth
glEnable_(#GL_FOG);									// Enables GL_FOG

AngleX.f
AngleY.f
AngleZ.f
X.f
Y.f
Z.f

Tex = LoadTexture_("C:\Downloads\Programming\OpenGL\lesson16\Lesson16\Data\Crate.bmp", 2)

Repeat
  Rot.f + 0.5
  
  glClear_(#GL_COLOR_BUFFER_BIT | #GL_DEPTH_BUFFER_BIT)
  
  glLoadIdentity_()
  SetCamera(45.0, 0.1, 100.0)
  
  glLoadIdentity_()
  glTranslatef_(X, Y, Z)
  glRotatef_(Rot, 1.0, 0.0, 0.0)
  
  DrawCube()
  
  SwapBuffers_(hDC)
  
  
  If GetAsyncKeyState_(#VK_UP)
    Z + 0.05
  ElseIf GetAsyncKeyState_(#VK_DOWN)
    Z - 0.05
  EndIf
  
  If GetAsyncKeyState_(#VK_LEFT)
    X - 0.05
  ElseIf GetAsyncKeyState_(#VK_RIGHT)
    X + 0.05
  EndIf
  
  Delay(10)
  
  Event = WindowEvent()
Until Event = #PB_Event_CloseWindow
End
EndIf

It works well here.
But forget to manipulate the PerspectiveMatrix with glTranslate glRotate then

the fog will always be at 0, 0, 0 and nowhere else.

Post by **Polo** » Fri Jul 01, 2005 11:45 am

Ok, so the problem was that I wasn't using glulookat ?
I don't want to use that crappy command

Thanks for the code, I hope I'll have it working

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