CS559
Fall 2005
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Lighting
Adapted from Stephen J. Chenney's Tutorial
Modified by Yu-Chi Lai at 2005
This tutorial will build on the previous tutorial, adding OpenGL colored
lighting.
- EnableLighting
- Position
the Light Source
- Setup Material
Properties
- Add Normals
- Build and
Run the Program
Lets get started.
Step 1: Enable Lighting
We're going to be using OpenGL lighting so the first thing to do is tell
OpenGL we need it to do the lighting calculations for the geometry we send
it. We do this by enabling lighting and enabling at least one OpenGL
light source. Our revised InitializeGL() method looks like this.
void MyWindow::InitializeGL()
{
glClearColor(.1f, .1f, .1f, 1);
glEnable(GL_DEPTH_TEST);
glEnable(GL_LIGHTING);
glEnable(GL_LIGHT0);
float lightColor[4]= {1, 1, 1, 1};
glLightfv(GL_LIGHT0, GL_DIFFUSE, lightColor);
}
We enable OpenGL lighting and enable the first light (GL_LIGHT0). We then set the lights diffuse
color to white. We won't use any ambient or specular light for this
tutorial.
Step 2: Position the Light Source
We'll need to position our light source so it illuminates our cube.
We add this code to our draw() method.
. . .
gluLookAt(0, 0, 3, 0, 0, 0, 0, 1, 0);
float lightPosition[4] = {5, 5, 5, 1};
glLightfv(GL_LIGHT0, GL_POSITION, lightPosition);
glRotatef(rotation, 0, 1, 0);
. . .
We've placed our light at (5, 5, 5) so it should shine on the upper right
corner of our cube. Notice the one trailing the light position.
This is the homogeneous coordinate and tells OpenGL we want a point light.
If it was a zero the light would be a directional light and the (5, 5, 5)
would specify the direction instead of a position.
Step 3: Setup Material Properties
When using OpenGL lighting we no longer set colors for our geometry.
We need to set material properties. However, for this simple demo
we can use some OpenGL functionality to use the colors we've already specified
as the material properties we need. This will convert our glColor3f()
calls to material property settings instead. We'll add this
to our InitializeGL() method. We need to enable
this functionality called color material and set the diffuse material
property to track the colors we've set with glColor3f().
. . .
float lightColor[4] = {1, 1, 1, 1};
glLightfv(GL_LIGHT0, GL_DIFFUSE, lightColor);
glEnable(GL_COLOR_MATERIAL);
glColorMaterial(GL_FRONT_AND_BACK, GL_DIFFUSE);
}
Step4: Add Normals
The only thing left to do is add normal vectors to each of
our quads that form the cube. We'll modify DrawCube()
to include normals.
void MyWindow::DrawCube()
{
glBegin(GL_QUADS);
// front
glNormal3f(0, 0, 1);
glColor3f(1, 0, 0);
glVertex3f(-1, 1, 1);
glVertex3f(-1, -1, 1);
glVertex3f(1, -1, 1);
glVertex3f(1, 1, 1);
// back
glNormal3f(0, 0, -1);
glColor3f(0, 1, 0);
glVertex3f(-1, 1, -1);
glVertex3f(1, 1, -1);
glVertex3f(1, -1, -1);
glVertex3f(-1, -1, -1);
// top
glNormal3f(0, 1, 0);
glColor3f(0, 0, 1);
glVertex3f(-1, 1, -1);
glVertex3f(-1, 1, 1);
glVertex3f(1, 1, 1);
glVertex3f(1, 1, -1);
// bottom
glNormal3f(0, -1, 0);
glColor3f(1, 1, 0);
glVertex3f(-1, -1, -1);
glVertex3f(1, -1, -1);
glVertex3f(1, -1, 1);
glVertex3f(-1, -1, 1);
// left
glNormal3f(-1, 0, 0);
glColor3f(0, 1, 1);
glVertex3f(-1, 1, -1);
glVertex3f(-1, -1, -1);
glVertex3f(-1, -1, 1);
glVertex3f(-1, 1, 1);
// right
glNormal3f(1, 0, 0);
glColor3f(1, 0, 1);
glVertex3f(1, 1, 1);
glVertex3f(1, -1, 1);
glVertex3f(1, -1, -1);
glVertex3f(1, 1, -1);
glEnd();
}
Step 5: Build and Run the Program
Ok we're ready to build and run our program.
Choose Build -> Build Solution
to compile and link the program and Debug
-> Start Without Debugging to run it.
Source code for this tutorial.
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