2D Transformations and the 2D Viewing Pipeline

Part 1: 2D Tranformations

The ability to perform transformations on objects in an image is an important feature of a graphics system. Operators were added to this system which allow the user to create 2D transformation matrices that perform the following transformations:

• scale around (0, 0)
• scale around an arbitrary point, with the x-scale direction oriented to a specified angle
• translate
• rotate around (0, 0)
• rotate around an arbitrary point

Part 2: The Starship Enterprise

The next task was to create an image of the Starship Enterprise by applying the transformation tools developed in the previous task to a unit circle and square. Below is the generated image.

Part 3: Animating the Starship Enterprise

The next step was to create an animation of the Enterprise orbiting a planet.

Part 4: The Viewing Pipeline

The final task consisted of creating a 2D viewing pipeline that would allow the designer to pan around the image. The animation below is an example of this feature. The viewing pipeline moves in a diamond shape that shadows the motion of the Enterprise.

Extensions

As an extension, we used the transformation matrices that we had created to make an animated gif of the Enterprise going to warp speed. The parts of the Enterprise are stretched and then shrunk over time, and a filled polygon was added at the end to create the effect of an explosion.

Questions

1. Who did you work with on this assignment, and what tasks did each of you do?
   I worked with Casey Smith, and we shared the work on most of the tasks.



2. Describe the mechanism you developed for handling the global transformation parameters and matrix.
   The "global transformation parameters" weren't really global, they were local to the test program. Each new graphics object had its own transformation matrix, and each of these was passed to the appropriate drawing function (polyLineM, drawUnfilledCircleM, drawFilledCircleM). The transformation was applied to the points in the the draw functions.



3. Describe the mechanism you developed for handling the viewing pipeline parameters and transformation matrix.
   For this assignment, the global transformation parameters were hardcoded into the test programs, and the matrix was constructed by translating and scaling the View Transformation Matrix using the translation and rotation functions. In the future, however, a function will be created that will take in the points at the lower left and upper right of the viewing window and the desired scale and will perform the translation and rotation on the VTM.



4. Once you had the code in place, what was the process and how difficult was it to modify the view window and the position of the Enterprise?
   The transformation functions made it very easy to move the objects in the scene and to change the view window. To change the position of the enterprise, simply apply the same translation or rotation to each piece of the figure. This will, of course, become even simpler when we have created a hierarchical modeling system in which individual graphical elements can be combined into one object and tranformed as a unit.
   Moving the viewing window is equally easy. Points are stored for the lower left and upper right corners of the view window, along with the desired dimensions of the output image. Changing the viewing window is as simple as changing the points for the corners of the viewing window and then applying the transformation matrix to the image objects (lines, circles, etc.).



5. If you extended this assignment in any way, describe what you did and how you did it. Include pictures, or links to pictures that show what you did. As an extension, we created an image of the Starship Enterprise going into warp speed (see above). We just created series of images in which the Enterprise was stretched, followed by a series of images in which it was collapsed into an explosion (a filled polygon).