Jeff Molofee - NeHe's OpenGL Tutorials

// Top Face

glNormal3f( 0.0f, 1.0f, 0.0f); // Normal Pointing Up

glTexCoord2f(0.0f, 1.0f); glVertex3f(-1.0f, 1.0f, –1.0f); // Point 1 (Top)

glTexCoord2f(0.0f, 0.0f); glVertex3f(-1.0f, 1.0f, 1.0f); // Point 2 (Top)

glTexCoord2f(1.0f, 0.0f); glVertex3f( 1.0f, 1.0f, 1.0f); // Point 3 (Top)

glTexCoord2f(1.0f, 1.0f); glVertex3f( 1.0f, 1.0f, –1.0f); // Point 4 (Top)

// Bottom Face

glNormal3f( 0.0f,-1.0f, 0.0f); // Normal Pointing Down

glTexCoord2f(1.0f, 1.0f); glVertex3f(-1.0f, –1.0f, –1.0f); // Point 1 (Bottom)

glTexCoord2f(0.0f, 1.0f); glVertex3f( 1.0f, –1.0f, –1.0f); // Point 2 (Bottom)

glTexCoord2f(0.0f, 0.0f); glVertex3f( 1.0f, –1.0f, 1.0f); // Point 3 (Bottom)

glTexCoord2f(1.0f, 0.0f); glVertex3f(-1.0f, –1.0f, 1.0f); // Point 4 (Bottom)

// Right face

glNormal3f( 1.0f, 0.0f, 0.0f); // Normal Pointing Right

glTexCoord2f(1.0f, 0.0f); glVertex3f( 1.0f, –1.0f, –1.0f); // Point 1 (Right)

glTexCoord2f(1.0f, 1.0f); glVertex3f( 1.0f, 1.0f, –1.0f); // Point 2 (Right)

glTexCoord2f(0.0f, 1.0f); glVertex3f( 1.0f, 1.0f, 1.0f); // Point 3 (Right)

glTexCoord2f(0.0f, 0.0f); glVertex3f( 1.0f, –1.0f, 1.0f); // Point 4 (Right)

// Left Face

glNormal3f(-1.0f, 0.0f, 0.0f); // Normal Pointing Left

glTexCoord2f(0.0f, 0.0f); glVertex3f(-1.0f, –1.0f, –1.0f); // Point 1 (Left)

glTexCoord2f(1.0f, 0.0f); glVertex3f(-1.0f, –1.0f, 1.0f); // Point 2 (Left)

glTexCoord2f(1.0f, 1.0f); glVertex3f(-1.0f, 1.0f, 1.0f); // Point 3 (Left)

glTexCoord2f(0.0f, 1.0f); glVertex3f(-1.0f, 1.0f, –1.0f); // Point 4 (Left)

glEnd(); // Done Drawing Quads

The next two lines increase xrot and yrot by the amount stored in xspeed, and yspeed. If the value in xspeed or yspeed is high, xrot and yrot will increase quickly. The faster xrot, or yrot increases, the faster the cube spins on that axis.

xrot+=xspeed; // Add xspeed To xrot

yrot+=yspeed; // Add yspeed To yrot

return TRUE; // Keep Going

}

Now we move down to WinMain(). Were going to add code to turn lighting on and off, spin the crate, change the filter and move the crate into and out of the screen. Closer to the bottom of WinMain() you will see the command SwapBuffers(hDC). Immediately after this line, add the following code.

This code checks to see if the letter 'L' has been pressed on the keyboard. The first line checks to see if 'L' is being pressed. If 'L' is being pressed, but lp isn't false, meaning 'L' has already been pressed once or it's being held down, nothing will happen.

SwapBuffers(hDC); // Swap Buffers (Double Buffering)

if (keys['L'] && !lp) // L Key Being Pressed Not Held?

{

If lp was false, meaning the 'L' key hasn't been pressed yet, or it's been released, lp becomes true. This forces the person to let go of the 'L' key before this code will run again. If we didn't check to see if the key was being held down, the lighting would flicker off and on over and over, because the program would think you were pressing the 'L' key over and over again each time it came to this section of code.

Once lp has been set to true, telling the computer that 'L' is being held down, we toggle lighting off and on. The variable light can only be true of false. So if we say light=!light, what we are actually saying is light equals NOT light. Which in english translates to if light equals true make light not true (false), and if light equals false, make light not false (true). So if light was true, it becomes false, and if light was false it becomes true.

lp=TRUE; // lp Becomes TRUE

light=!light; // Toggle Light TRUE/FALSE

Now we check to see what light ended up being. The first line translated to english means: If light equals false. So if you put it all together, the lines do the following: If light equals false, disable lighting. This turns all lighting off. The command 'else' translates to: if it wasn't false. So if light wasn't false, it must have been true, so we turn lighting on.

if (!light) // If Not Light

{

glDisable(GL_LIGHTING); // Disable Lighting

} else // Otherwise

{

glEnable(GL_LIGHTING); // Enable Lighting

}

}

The following line checks to see if we stopped pressing the 'L' key. If we did, it makes the variable lp equal false, meaning the 'L' key isn't pressed. If we didn't check to see if the key was released, we'd be able to turn lighting on once, but because the computer would always think 'L' was being held down so it wouldn't let us turn it back off.

if (!keys['L']) // Has L Key Been Released?

{

lp=FALSE; // If So, lp Becomes FALSE

}

Now we do something similar with the 'F' key. if the key is being pressed, and it's not being held down or it's never been pressed before, it will make the variable fp equal true meaning the key is now being held down. It will then increase the variable called filter. If filter is greater than 2 (which would be texture[3], and that texture doesn't exist), we reset the variable filter back to zero.

if (keys['F'] && !fp) // Is F Key Being Pressed?

{

fp=TRUE; // fp Becomes TRUE

filter+=1; // filter Value Increases By One

if (filter>2) // Is Value Greater Than 2?

{

filter=0; // If So, Set filter To 0

}

}

if (!keys['F']) // Has F Key Been Released?

{

fp=FALSE; // If So, fp Becomes FALSE

}

The next four lines check to see if we are pressing the 'Page Up' key. If we are it decreases the variable z. If this variable decreases, the cube will move into the distance because of the glTranslatef(0.0f, 0.0f, z) command used in the DrawGLScene procedure.

if (keys[VK_PRIOR]) // Is Page Up Being Pressed?

{

z-=0.02f; // If So, Move Into The Screen

}

These four lines check to see if we are pressing the 'Page Down' key. If we are it increases the variable z and moves the cube towards the viewer because of the glTranslatef(0.0f, 0.0f, z) command used in the DrawGLScene procedure.

if (keys[VK_NEXT]) // Is Page Down Being Pressed?

{

z+=0.02f; // If So, Move Towards The Viewer

}

Now all we have to check for is the arrow keys. By pressing left or right, xspeed is increased or decreased. By pressing up or down, yspeed is increased or decreased. Remember further up in the tutorial I said that if the value in xspeed or yspeed was high, the cube would spin faster. The longer you hold down an arrow key, the faster the cube will spin in that direction.

if (keys[VK_UP]) // Is Up Arrow Being Pressed?

{

xspeed-=0.01f; // If So, Decrease xspeed

}

if (keys[VK_DOWN]) // Is Down Arrow Being Pressed?

{

xspeed+=0.01f; // If So, Increase xspeed

}

if (keys[VK_RIGHT]) // Is Right Arrow Being Pressed?

{

yspeed+=0.01f; // If So, Increase yspeed