Homework 5

For this assignment, we implemented a heirarchical modeling system in two dimensions.

Tasks

We began by developing the Module structure. A Module contians a linked list of drawing instructions for calls to primitives with their arguments. The user begins by openning a Module and calling graphics primitives. The primitive functions called aren't drawn immediately, however. They are added to the draw record for the Module and are only drawn when the DrawModule() function is called outside of any open Modules. This allows for proper matrix manipulation of the points and heirarchical Modules (Modules containing other Modules which contain other Modules, etc.). Once our primitives and matrix manipulations were rewritten to follow this scheme, drawing and manipulating complex (comparatively) scenes became easy. We also created a View Transformation Matrix and manipulators to allow for the conversion of real-world coordinates to screen (ppm) cooridinates.

The first required image is the starship enterprise rendered with the Module system:

Each element is a Module, and there is an over-arching enterprise Module containing all the elements. Above that is a scene Module which sets the VTM.

The second required image is a formation of three enterprises rendered several times:

This image only has one enterprise Module, but the module is used three times to create a formation Module, which is in turn used three times to create the fleet.

Extensions

For extensions, I made some pretty pictures:

Fun with the VTM.


Captain! I can't hold her steady!


More fun with the VTM.


A crowd scene.

Questions

  1. Describe your model structure data type.
    Our "Modules" contain a linked list of "Graphic Elements". The GraphicElement structure contains an opcode (unique int for each drawing function), the number of arguments, and an array of the arguments. The array is a union of a few different possible arguments.
  2. Describe the operation of your DrawStructure routine.
    The DrawModule routine starts by checking to see if there is a module open. If there is, it merely adds itself to the current draw record. If not, it starts the drawing process. After setting the local transformation matrix to the identity matrix, it starts executing the operations stored in the GraphicElement linked list. Using a switch statement, it chooses its actions based on the opcode. Most operations are straightforward, but drawing another module within the record is a little bit subtle. The gtm and pen color and fill color must be saved before recursively calling the DrawModule function on the Module listed in the linked list. Then, the gtm and colors are restored. All other cases merely extract the arguments and call the appropriate function.
  3. What extensions did you do for this assignment, how did you do them, and how well did they work?
    I made some animated gif scenes for my extensions. They worked pretty well, as you can see above. For the first one, I expanded the view window at an increasing rate, moving slightly backwards all the while to make it look a little bit like the ships are moving. For the second, I just made the ship rotate around a planet and rotate around its own axis at four times that rate. For the final one, I made the view window follow the spinning ship.
    I also made a "crowd" scene of stick figures. The person is a Module, and the height and location are varied so that the further down on the image the person is, the larger it will appear, with a bit of randomness thrown in.