Assignment 1

Handed out:	Thursday, January 15, 1998
Due:	5pm, Thursday, January 29, 1998

Your assignment is to implement an impressionistic paint system, similar in spirit to Paul Haeberli's The Impressionist (this program exists as a Java Applet). Please try out Haeberli's program to get a feel for how the system should work.

Your version of the The Impressionist program will load a full color image, allow the user to create a painting, and then save the resulting image. The painting, unlike the original image, will consist of a set of brush strokes: each stroke will have a color, a shape, a position, a size and an orientation. The strokes will be created by the user, by sweeping the mouse over the image, in the process picking up the color from the original image and laying down a stroke at the cursor location.

Your system should have the following features.

• Provide a palette of at least three brush shapes. The following three shapes are required: a circle, a rectangle rotated by 45 degrees, and a scattered collection of lines.
• Provide a control so that the user can set the size of the brush.
• Provide at least three methods for controlling the position and orientation of the brush. The first, and simplest, method should be to place the brush at the current cursor location in a fixed orientation. The second method should orient the brush in the direction of mouse motion. The final method should continually jitter (randomly perturb) the position and orientation of the brush about the cursor location.
• Provide a blending mode. This requires that you provide a controller for setting the opacity to a value between 0 and 1. The opacity will control the transparency of the brush stroke. If the stroke is opaque (opacity equals 1), then the stroke will overwrite the current painted colors; if the stroke is transparent, it will be blended into the painting using the "over" operator.

To help you get started, and to help you concentrate on the more interesting aspects of this assignment, we will provide a sample program and a collection of interesting images. The sample program will read in a full color image, and store the image in a 2D array. This program will also implement a clear button that erases the canvas, and a save button (that saves the painting in a file).

70% of your grade will be based on the features that you implement. That is, you will lose points for each of the above features that does not work correctly. 20% of your grade will be based on the the "look and feel" of your program. Your program should be zippy, and not sluggish. Your program should also have a "reasonable, but not fancy" user interface (glut popup menus and keyboard controls are fine). And finally 10% of your grade will be based on programming style; in particular, we may take off points for obfuscated code, or very inefficient use of OpenGL.

Extra Credit. Up to 10 points of extra credit are available for implementing novel, and unique extensions to the base assingment. To apply for extra credit, write a one paragraph description of what you have come up with, and why you think it is interesting. Only highly original ideas will be awarded extra credit.

Here are a few suggestions:

• Add brushes that are substantially different from those ou are required to implement. Explain how your brushes are different and the types of effects they allow you to create.
• It can be time-consuming to paint an image manually. Add a feature so that a whole painting can be created automatically. Describe your algorithm for choosing the brush attributes in this automatic painting mode.
• One problem with the base system is that you can not see which part of the image you are painting while you paint. Solve this problem by showing a dimmed version of the original image while you paint. Add controls to show/remove the dimmed image from the canvas.
• Add methods for orienting the brush to the x,y color gradient or the edges in the original image.
• Automatically find edges in the original image and clip long brush stokes to those edges.

Note that some of these suggestions are much more difficult to implement than others. We will judge the amount of extra credit you receive accordingly.