1	CS 248 Assignment 1 Paint Program CS248 Help Session #1 Gaurav Garg Stanford University October 5, 2005 Original slides by Georg Petschnigg Modified by: Sean Walker, Rene Patnode Gaurav Garg
2	Session Overview Getting Started Assignment Discussion Overpainting Brush Tinting Brush Brush Visualization Grading Details Extra Credit Questions
3	Getting Started Read assignment carefully and pay attention to the details Go to help session Familiarize yourself with Graphics Cluster (2^nd Floor) in Sweet Hall Lookout for Myths/Raptors/Firebirds (Myths are latest and greatest)
4	Where to work from? Sweet Hall Work from home Reproduce Sweet Hall Lab development environment on you own Machine Your code still has to work on the Sweet Hall machines (more risk for you)
5	Sweet Hall Pick a free computer, Log on Copy assignment from /usr/class/cs248/assignments/assignment1/ to local directory Run ‘make’ Run ‘./paint.i386-linux’
6	Working Remotely ssh to firebird, raptor or leland (make sure X-tunneling is enabled) Detailed instructions on following page: http://graphics.stanford.edu/courses/cs248-05/remote.html
7	Assignment Discussion You are going to write a paint program Teaches you 2D Raster Graphics Visualize concepts learned in Class (Brushes, HSV) Be creative with extra credit The next slides follow the Assignment (Handout #3) step by step Reminder: Read the assignment
8	Paint Program 1973
9	Part 1: Over Painting Brush Rectangular Overpainting Brush Like Microsoft Paint or “Pencil Tool” in PhotoShop Color Picker for RGB, HSV See http://java.sun.com/docs/books/tutorial/uiswing/ components/colorchooser.html or any commercial paint program Value (1.0 bright, 0.0 black) Saturation (1.0 strong hue, 0.0 faded hue) Size Control for Brush Demo: Painting, Picking Colors in Photoshop
10	Part 1: Basic Painting Loop
11	Part 1: Over Painting Brush Once you are done with Part 1 you should be able to draw some basic images Notice the hard edges and jaggies around the stroke… this is what Part 2 will fix
12	Part 2: Tinting Brush Implement Weighted Mask Driven Brush as described in Handout #4 Instead of a rectangular brush, have it gently “blend” to its surroundings. Use HSV interpolation Checkboxes for interpolating along H,S,V axis Allow all permutations HSV, HS, HV, SV, H, S, V Choose a mask function and give user control over it Make sure it gradually falls off to zero at edges!
13	Part 2: Weighted Blending Like painting with partially transparent paint. Commonly referred to as “alpha” blending.
14	Part 2: Mask driven painting Lookup array determines how each pixel in the brush is affected.
15	Part 2: Weighted mask driven painting Mask contains alpha/weight for each pixel in brush
16	Part 2: RGB vs. HSV interpolation
17	Part 2: RGB vs. HSV
18	Part 2: RGB vs. HSV interpolation
19	Part 2: Math Example Interpolating half way between Red and Cyan (a = 0.5) NewColor = 0.5 Cyan + 0.5 Red Demo: Blending in Photoshop
20	Part 2: HSV Checkboxes Choose which HSV components to affect. Allow for any combination. if (H_check) NewH = (1-a) CH + a PaintH else NewH = CH; if (S_check) NewS = (1-a) CS + a PaintS else NewS = CS; if (V_check) NewV = (1-a) CV + a PaintV else NewV = CV;
21	Part 3: Brush Visualization Brush Visualization should tell user what its color, falloff and size is Brush should always be visible regardless of color Draw 1x (actual size) and 4x (four times larger in x and y) versions of the brush Make the larger version discretized – that is it should be a choppy/chunky/pixel replicated version of the actual brush (think xmag, snoop) Make sure this visualization will help you explain to user, TAs, Professor and yourself how the brush weights affect drawing
22	Requirements Correctness (40%) Don’t crash Implement all required features (Read the directions like a lawyer) Efficiency (20 %) No noticeable lag while using your application User Interface (20%) Programming Style (20%) Copying code (Don’t do it) Submitting with ‘/usr/class/cs248/bin/submit’
23	Extra credit example Blurring:
24	Questions? Ask now Come to Office Hours Newsgroup: su.clss.cs248 Email: cs248-aut0506-tas@lists.stanford.edu Remember: Computer Graphics is fun - if you are not having fun ask TAs for help