14. OpenGL Fog
To get started we need some variables for the fog colour and
the density of the fog. I have done it with this:
GLfloat density = 0.3;
GLfloat fogColor[4] = {0.5, 0.5, 0.5, 1.0};
The fog colour is written in four parts, they cover the RGB values
Unfortunately I have been unable to find out what the fourth value
does. Next we have the density which sets how thick our fog is.
If you run the application you can acctually see that a density of 0.3 is acctually
quite thick.
After this we enable our fog and set its parameters.
First off we enable the fog.
glEnable (GL_FOG);
Now we set the fog mode, here i have set it to GL_EXP2, which is quite nice looking.
glFogi (GL_FOG_MODE, GL_EXP2);
Here we set the actual colour of our fog.
glFogfv (GL_FOG_COLOR, fogColor);
Now the density.
glFogf (GL_FOG_DENSITY, density);
And here I have set it up to look the nicest. In large projects, this may slow
down you application.
glHint (GL_FOG_HINT, GL_NICEST);
There are a few other options but I will explain them in the next Fog tutorial.
I will just let you get a grasp at this basic concept before I complicate it
just a little more.
If you have any problems, please email me at swiftless@gmail.com
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#include <GL/gl.h>
#include <GL/glut.h> GLfloat angle = 0.0; GLfloat density = 0.3; //set the density to 0.3 which is GLfloat fogColor[4] = {0.5, 0.5, 0.5, 1.0}; //set the for void cube (void) { glRotatef(angle, 1.0, 0.0, 0.0); glRotatef(angle, 0.0, 1.0, 0.0); glRotatef(angle, 0.0, 0.0, 1.0); glColor3f(1.0, 0.0, 0.0); glutSolidCube(2); } void init (void) { glEnable (GL_DEPTH_TEST); //enable the depth testing glEnable (GL_FOG); //enable the fog glFogi (GL_FOG_MODE, GL_EXP2); //set the fog mode to GL_EXP2 glFogfv (GL_FOG_COLOR, fogColor); //set the fog color to glFogf (GL_FOG_DENSITY, density); //set the density to the glHint (GL_FOG_HINT, GL_NICEST); // set the fog to look the } void display (void) { glClearColor (0.0,0.0,0.0,1.0); glClear (GL_COLOR_BUFFER_BIT | GL_DEPTH_BUFFER_BIT); glLoadIdentity(); gluLookAt (0.0, 0.0, 5.0, 0.0, 0.0, 0.0, 0.0, 1.0, 0.0); cube(); glutSwapBuffers(); angle ++; } void reshape (int w, int h) { glViewport (0, 0, (GLsizei)w, (GLsizei)h); glMatrixMode (GL_PROJECTION); glLoadIdentity (); gluPerspective (60, (GLfloat)w / (GLfloat)h, 1.0, 100.0); glMatrixMode (GL_MODELVIEW); } int main (int argc, char **argv) { glutInit (&argc, argv); glutInitDisplayMode (GLUT_DOUBLE | GLUT_RGBA | GLUT_DEPTH glutInitWindowSize (500, 500); glutInitWindowPosition (100, 100); glutCreateWindow (“A basic OpenGL Window“); init (); glutDisplayFunc (display); glutIdleFunc (display); glutReshapeFunc (reshape); glutMainLoop (); return 0; } |
can you tell something about GL_FOG_INDEX
where and why it is used and for what…
fog is deprecated in opengl 3.1 and above.
afortunately it’s simple to do the fog effect in vetex/fragment shaders.
Hi, these tutorial are really good 🙂 they’re simple too 😉 However, I see you don’t know what the fourth parameter of the fog color stands for. It is simply the Alpha value, in fact you pass for parameters, R(ed), (G)reen, (B)lue and (A)lpha. I’m basing on the Red Book, “OpenGL Programming Guide”, Sixth Edition, page 265.
Hey Michael,
Thanks. They were initially designed to be super simple, showing off each method. Careful with what you say I don’t know though 😉 These tutorials (Version 1.0) are about 5 years older than the post date, the post date is just when it was moved over to a WordPress back end. These were effectively written by me at about the age of 13-15.
You’re definitely correct about the fourth parameter being the Alpha value. That holds true in everything colour related, where the older versions of OpenGL (from the time this was written) allowed you to set either RGB or RGBA, the newer versions of OpenGL, 3.x and 4.x assume you handle all colours yourself inside of your shaders. Because you were allowed to skip the A value in the fixed pipeline, I believe I skipped it in a few of these tutorials. I don’t mention Alpha values until a specific tutorial.
Cheers,
Swiftless
@”A Man”: A simple piece of code I took from another OpenGL tutorial limits the frame rate:
bool limitFpsTo(int rate){
static float last = GetTickCount() * 0.001f;
static float elapsed = 0.0f;
float currect = GetTickCount() * 0.001f;
float delta = currect – last;
float FPS = 1.0f/rate;
elapsed+=delta;
last=currect;
if (elapsed>FPS)
{
elapsed -=FPS;
return true;
}
return false;
}
If you place the buffered keyOperations() function introduced in Tutorial 3 inside the if(limitFpsTo) in the display() function the speed should be fixed.
Hey!
i have prob. with this tut. I have lighting too and when try fog everything drawn becomes black. I can’t understand why…
Do u know what problem might be?
Object too far away? Haven’t set your “fogColor” array var up with 0.5,0.5,0.5,1 (four values)?
Also try “glClearColor(0.5, 0.5, 0.5, 1);” prior — makes the background gray to match the fog. Otherwise, yes, yr background will be black.
on my computer the cube rotate very fast so i changed
this
angle ++;
to
angle += 0.01
Hi A man,
Depending on the speed of your machine, you will always have to change this. To make it constant on every machine, you need to use some time-based techniques. Such as incrementing angle depending on how much time has passed since the last frame.
Thanks,
Swiftless
Heya, cool tutorials, keep them up!
btw, I think the fourth value in your fog color is the alpha value, obviously it will only make a change if you have blending enabled. Could be interesting to see if it blends with your glClearColor aye? 🙂
Hey, nice tutorials. On tutorial 14 “OpenGL Fog” The intro is repeated twice. Just so you know.
Thanks for the heads up Ted, I’ll fix that up.
Cheers,
Swiftless