Spot lights...

[savage]

Ok it seems the reason why my light was not working properly was because my quad was not tessallated enough ( from http://www.opengl.org/resources/feat...es/oglpitfall/ ).

Ok I have that appearing with...
[pascal]
// Start Drawing Our Quads
glBegin(GL_QUADS);
for i := 0 to 43 do
begin
for j := 0 to 43 do
begin
w := 1 / 44 * Application.Width;
h := 1 / 44 * Application.Height;
glTexCoord2f((i+1)/GridWidth, (j+1)/GridHeight); glVertex3f( (i+1)*w, (j+1)*h,0);
glTexCoord2f((i+1)/GridWidth, j /GridHeight); glVertex3f( (i+1)*w, j *h,0);
glTexCoord2f( i /GridWidth, j /GridHeight); glVertex3f( i *w, j *h,0);
glTexCoord2f( i /GridWidth, (j+1)/GridHeight); glVertex3f( i *w, (j+1)*h,0);
end;
end;
glEnd();
[/pascal]

Ok but my light still does not appear properly.

I currently have a SpotLight record set as follows...
[pascal]
TLight = record
amb : array[0..3] of GLFloat;
diff : array[0..3] of GLFloat;
spec : array[0..3] of GLFloat;
pos : array[0..3] of GLFloat;
spotDir : array[ 0..2 ] of GLfloat;
spotExp : GLfloat;
spotCutoff : GLfloat;
atten : array[ 0..2 ] of GLfloat;

trans : array[ 0..2 ] of GLfloat;
rot : array[ 0..2 ] of GLfloat;
end;
[/pascal]
and populating it as follows...
[pascal]
// ambient
SpotLight.amb[0] := 0.2;
SpotLight.amb[1] := 0.0;
SpotLight.amb[2] := 0.0;
SpotLight.amb[3] := 1.0;

// diffuse
SpotLight.diff[0] := 0.8;
SpotLight.diff[1] := 0.0;
SpotLight.diff[2] := 0.0;
SpotLight.diff[3] := 1.0;

// specular
SpotLight.spec[0] := 0.4;
SpotLight.spec[1] := 0.0;
SpotLight.spec[2] := 0.0;
SpotLight.spec[3] := 1.0;

// position
SpotLight.pos[0] := 0.0;
SpotLight.pos[1] := 0.0;
SpotLight.pos[2] := 0.0;
SpotLight.pos[3] := 1.0;

// direction
SpotLight.spotDir[0] := 0.0;
SpotLight.spotDir[1] := 0.0;
SpotLight.spotDir[2] := -1.0;

// exponent
SpotLight.spotExp := 20.0;

// cutoff
SpotLight.spotCutoff := 60.0;

// attenuation
SpotLight.atten[0] := 1.0;
SpotLight.atten[1] := 0.0;
SpotLight.atten[2] := 0.0;

// translation
SpotLight.trans[0] := 0.0;
SpotLight.trans[1] := 1.25;
SpotLight.trans[2] := 0.0;

// rotation
SpotLight.rot[0] := 0.0;
SpotLight.rot[1] := 0.0;
SpotLight.rot[2] := 0.0;
[/pascal]

and I'm setting the light as follows
[pascal]
glLightfv(GL_LIGHT0, GL_POSITION, @SpotLight.pos);
glLightfv(GL_LIGHT0, GL_SPOT_DIRECTION, @SpotLight.spotDir);
[/pascal]

Why is my light not appearing when I use glOrtho for projection?
I know there are other ways to get this effect, but I really want to learn how to do it with OpenGL lighting. I just want the spot light to shine on a small portion of the background texture, or another example would be for the light to only highlight the bits of the background texture that the mouse is over. I'm sure you are all familiar with the effect.

I think my problem is my understanding of the co-ordinate system as it applies to glOrtho. With gluPerspective I sort of understand you need to use small decimal values, but with glOrtho I not sure if that is still the case or not. I think I need to go back to OpenGL school. Can anyone shed some light ( not pun intended ) on the situation?

[Paulius]

Did a quick test, it works for me
[pascal]
pos[0]:= 0.0;
pos[1]:= 0.0;
pos[2]:= 0.0;
pos[3]:= 1.0;

Dir[0]:= 0.0;
Dir[1]:= 0.0;
Dir[2]:= -1.0;

glLightfv(GL_LIGHT0, GL_POSITION, @pos);
glLightfv(GL_LIGHT0, GL_SPOT_DIRECTION, @Dir);
glLightf(GL_LIGHT0, GL_SPOT_CUTOFF, 60);
glLightf( GL_LIGHT0, GL_SPOT_EXPONENT, 20.0);

glenable(Gl_LIGHTING);
glenable(GL_LIGHT0);
glMatrixMode(GL_PROJECTION);
glloadidentity();
glOrtho(0, 1, 0, 1, 10, -10);

glBegin(GL_QUADS);
for i:= 0 to 43 do
begin
for j:= 0 to 43 do
begin
w := 1 / 44;
h := 1 / 44;
glVertex3f((i+1) * w, (j+1) * h, -1);
glVertex3f( i * w, (j+1) * h, -1);
glVertex3f( i * w, j * h, -1);
glVertex3f((i+1) * w, j * h, -1);
end;
end;
glEnd;[/pascal]

[savage]

My glOrtho is set to [pascal]glOrtho( 0.0, width, height, 0.0, -1.0, 1.0 );[/pascal]

What is the advantage is there in using your implemenation over mine?

[Paulius]

Height and width are constants just out of my preference to keep things resolution invariant. Top is more than bottom naturally, if done the other way around winding order changes.
Edit: I used zNear and zFar incorrectly, it should be like yours near < far