CMPS 160 -- Spring 2015

CMPS 160 -- Program 3

Due date:
Midnight, Friday, May 15, 2015
Early bonus: before midnight, May 14.
Late submission until midnight, May 16.

Objectives:

Apply basic transformations to objects in the scene.

Description

The new things for this assignment are: (a) direct or indirect manipulation for objects, and (b) cumulative transformations.
For this assignment, you will still render the shark model, but will create more than one instance of them (i.e. must have at least 2 sharks in your scene). Your code must distinguish between the different shark instances allowing the user to pick (see lab4) a specific shark. Once a shark is selected, user can specify basic transformations (translate, rotate, scale) to be applied to it. This capability should allow the user to ``compose'' the scene.
Parameters for the transformations can be supplied in one of two ways. (a) sliders, or (b) combination of buttons and mouse movements. Sliders are easier to implement though the interaction is indirect. One way to do this is have separate sliders for different translations along x, y, and z. Another set of sliders for specifying scaling factors along x, y, and z (be careful with scaling by 0). And yet another set of sliders for rotation amounts around the x, y, and z axes. That's a lot of sliders. Typically, this type of interaction supports scaling with respect to the current location of the object i.e. object changes volume in place without getting its center moved elsewhere. Also typical of slider interaction is rotation about the object's axes as opposed to the world axes. Rotations are also done in-place.
An alternative way is with direct manipulation similar to the drag-and-drop interface. Translation could be specified with left button down together with mouse movements. Scaling is usually done with middle button down together with mouse movements. Rotations can be done with right button and mouse movement. Since mouse movements are constrained to produce 2 values only (screen x and y movements) whereas our transformations require 3 values, some assumptions/tradeoffs need to be made. For example, scaling can be limited to uniform scaling, where the mouse movement to the right and/or up implies increasing the scale factor, and mouse movement to the left and/or down implies decreasing the scale factor. For translation, horizontal and vertical mouse movements can be mapped directly to x and y translations in world space. For z translation, perhaps the letter z need to be pressed in conjunction with mouse movements where the motions are similar to scaling. That is, translate positive z for right and/or up mouse movements, etc. For rotation, a combination of keyboard, button and mouse movements can be use to specify +/- in-place rotations about the three axes one at a time.
For the different transformations, and whether they are done via indirect or direct manipulation, the effects of the different transformations should be cumulative. That is, if I've scaled an object already, and I later pick it again and move it, the scaled object is moved to the new location, etc. The standard way to do this is by maintaining a composite matrix per object. Subsequent transformations are ``added'' to the composite matrix.
Bonus, 20 points more for prog3: Instead of using a combination of keyboard, button and mouse for specifying rotations, it's possible to do this more intuitively with just button and mouse. The trick is to use the direction of the mouse movement on the display screen to implicitly specify an axis of rotation that is perpendicular to the swipe motion. For example, if I move the mouse from left-to-right, then this means I want to rotate the object about its center (where ever it is currently on the screen) about an axis that is vertical with respect to the screen. Moving the mouse from right-to-left is rotation about the same axis but in opposite direction.

Grading:

This program will form part of your CMPS 160 grade. The other components of CMPS 160 grade are your midterms and final project.

The header block should contain at least the following information: name, cruzid, date, and brief description of your program. This will be true for all future assignments and programs.

Rubric:


5	header blocks
5	code readability
10	inline comments
20	translation
20	scaling
20	rotation
20	cumulative transformation
20	bonus

Who graded your assignment:

jiayu: ahosick -- jbernay
matthew: jchen160 -- tmlinejo

Submission:

Submission must be done using the "submit" command from CATS.

submit cmps160-ap.s15 prog3 prog3.tar, or
submit cmps160-ap.s15 prog3 prog3.zip

This command should work from unix.ic.ucsc.edu. Create and submit a subdirectory called prog3.
IT SHOULD CONTAIN ALL THE FILES NECESSARY FOR THIS PROGRAM TO RUN.
Tar or zip up prog3 before submitting.