Lab#3A:Simple Static Scenes Viewed from a Moving Camera with Perspective Projection

 

Goal: Download this demo project as a basic framework and develop a moving-camera version of your approximate circles in Lab#1.

 

 

  1. Model-view transformation: Explore the source code of the demo project about a static 3D scene viewed from a moving camera. Understand how gluLookAt (coming after glMatrixMode(GL_MODELVIEW) ) can introduce the viewing-transformation effect of changing the eye location, the center to look at, and the up vector of the camera and how to create the effect of a moving camera around the origin on the y=0 plane. You may want to play with projection.exe from Nate Robinís tutor repository to clarify your understanding of gluLookAt.

 

 

  1. Projection transformation: Instead of glOrtho in the sample code, please change it to gluPerspective or glFrustum to view the scene with perspective projection instead of orthographic projection. You may want to play with projection.exe from Nate Robinís tutor repository to see the effects of gluPerspective or glFrustum versus those of glOrtho, and thus clarify your understanding of the difference between orthographic projection and perspective projection. Note that these commands come after glMatrixMode(GL_PROJECTION) to introduce the projection-transformation effect.

 

  1. Add your own keyboard call-back function such that the user can increase or decrease the rotational speed of the camera by pressing the keys j or k respectively.

 

  1. Enhance the keyboard call-back function such that the user can increase or decrease the radius of orbit of the rotating camera by pressing the keys i or m respectively.

 

  1. Enhance the keyboard call-back function such that the user can let the camera revolve around the origin on either one of the three planes x=0, y=0, or z=0 by pressing either one of the three keys x, y, or z respectively. In other words, rotating around the x axis, the y axis, and the z axis respectively.Note that be careful about the setting of the up vector in gluLookAt. When rotating around the y axis, the up vector should always be set as (0,1,0). However, when rotating around either the x axis or the z axis, you need to handle this carefully:

 

    1. When rotating around the x axis, the x coordinate of the camera is always 0 while the y coordinate and the z coordinate of the camera keep changing according to a changing angle parameter theta. In other words, we have x=0, y=radius*cos(theta) and z= radius*sin(theta). Let PI be 3.14 in radian. Set the up vector as <0, cos(theta+PI/2), sin(theta+PI/2)>, which is PI/2 (90 degrees) ahead of theta and thus perpendicular to the viewing direction from the camera to the origin as the center.
    2. When rotating around the z axis, the z coordinate of the camera is always 0 while the x coordinate and the y coordinate of the camera keep changing according to a changing angle parameter theta. In other words, we have x=radius*cos(theta), y= radius*sin(theta), and z=0. Let PI be 3.14 in radian. Set the up vector as <cos(theta+PI/2), sin(theta+PI/2), 0>, which is PI/2 (90 degrees) ahead of theta and thus perpendicular to the viewing direction from the camera to the origin as the center.††

 

 

  1. Comments: For step 5 above, you are not required to make a smooth transition from moving around the origin on one orbit to another orbit when the user presses x, y, or z on the keuboard. In other words, a sudden discrete shift of the camera from is acceptable when the mouse events trigger such changes of orbits. However, there are ways to write code to make this transition very smooth. For example, you can have variables to remember what the new current target plane (x=0, y=0, or z=0) and previous target plane (x=0, y=0, or z=0) are respectively. When the current camera location is still on the previous orbit plane but not on the new orbit plane, keep moving the camera on the old orbit plane until the camera reach the a point on the intersection of the two orbit planes. Then you can really start moving the camera around the new orbit plane.

 

  1. Submit your source code together the self-evaluation report under Canvas.

 

 

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In addition to the graphics commands listed in the end of lab#1.

Spend time exploring the following functions.

 

glut functions: for registrating the call-back functions and posting a redisplay flag

 

 

glut functions: for swapping display buffers and