1. What you will learn about today
Cameras in OpenGL
Where this fits into world transformations
Various types of cameras

2. What is moving?
frame1
frame3
frame2

3. Let’s Examine the Camera
If I gave you a world, and said I want to render it from another viewpoint, what information do I have to give you?
Position
Which way we are looking
Which way is “up”
Aspect Ratio
Field of View
Near and Far

4. glm::lookat Orients and positions the “camera”
lookat( eyex, eyey, eyez,
centerx, centery, centerz, upx,upy, upz);
eye – the position of the camera in world coordinates center – the camera is pointed at this point
up – the direction defined to be up for the camera

5. Moving the camera How can we translate the camera?
add a vector to the eye and center parameters How far will this move it?
the length of the vector
What happens if you don’t change the center?
the camera will stay fixed on the original point

6. Camera without glm::lookat?
How can we translate and orient the camera without lookat?
inverse transforms: translate(-x,-y,-z); rotate(-angle, a,b,c) Where does this go in your openGL program (using lookat or not)?
usually at the beginning of your display function

7. Camera: side view
View Right
View Up
View Normal
View Direction

8. Camera: looking through the camera
View Up
View Right
What are the vectors?

9. Transformation World->Camera
View Right = u
1 0 0  camerax 
0 1 0
0 0 1
0 0 0
View Up = V
camera 
T  
y 
cameraz     1
n  N  (n , n , n ) N
1 2 3
u  V  N  (u , u , u )
V  N
1 2 3
View Direction = -N
v  n  u  (v1 , v2 , v3 )
u1 u2 u3 0
v v v 0
R  
3 
n1 n2 n3 0
 
1 2  
MW CVC  R  T

10. First Person Camera How is this implemented? Where is the ‘eye’?
What is the look at point?
What is up? up
center
eye

11. First Person Camera How do we move the camera?
Add a vector to eye and center up
move dir
center
eye

12. First Person Camera How do we rotate the camera?
Move the center point - add a vector to it
Up vector
Side vector: lookat x up
center up
eye

13. Lookat implementation oddities
What will happen if up == lookat direction?
Spins around the up axis in a weird way
Why does this happen?
Two axes of your camera frame are aligned!
How can we avoid this?
Maintain an orthogonal camera frame - Reset the up vector using lookat X side (e.g., more common in flight games)
Constrain the lookat direction to not get to close to the up vector (e.g., common in FPS games)
Use quaternions

14. 3rd Person Camera How is this implemented? Where is the ‘eye’?
What is the look at point?
What is up?

15. 3rd Person Camera Remember, initially the camera is
At the origin looking down –z)
• Same as glm::lookat(0,0,0, 0,0,-1,0,1,0)
How can this be more easily implemented without glm::lookat?
translate the character so you can see it
Draw the character
Rotate the world around Y at the fixed point of the character
Translate the world inversely to the character position
Render the world

16. Birds Eye Camera How is this implemented? Where is the ‘eye’? •
What is the look at point?
What is up?

17. Review: What you learned about today
Cameras in OpenGL
Where this fits into world transformation
The camera transform is performed after the world transform
IS THE SAME AS:
The camera is always at 0,0,0 looking down –z
The world transforms instead
Various types of cameras
1st, 3rd, birdseye