Lab Week 04 - Fall 2023

Tuesday, September 19, 2023


Introduction

Remember: As you work on these steps with guidance from your teaching assistant, you should look toward your neighbor to see if they need help (or ask if you need help). You can collaborate in lab during these activities!

In this lab, you will


Create a folder for this lab in your 15-104 folder/directory..


Problem A: Rotating Squares

Write a p5.js program that displays four white squares, each rotating clockwise around the center of each quadrant of a gray canvas. The initial configuration when the program draws the squares for the first time is this:

Initial configuration of four squares that will be rotating clockwise

The rectangles are drawn on a 400 x 400 canvas with centers at (100,100), (100, 300), (300, 100), and (300, 300). All rectangles start at a 45 degree angle. You should draw all four rectangles using the same function call in p5.js: 

rect(0, 0, 100, 100);

In order to draw all four rectangles using the same command above, you will need to use translation and rotation to get all four rectangles to appear in their correct positions. Don't forget to use push() and pop() before and after each rectangle drawn, or the transformations will accumulate!

To create the spinning effect, you should rotate each shape an extra 2 degrees for each frame drawn by the draw function. (Remember to repaint the background at the start of the draw function or you will have lots of rectangles being drawn.)

Review the notes on transformations since there is a problem that is very similar to this assignment that we discussed in class. (HINT: Use rectMode(CENTER) in your setUp() function to make it easier to draw the rectangles since you know their center rotation points.)

Here is a short movie that shows what the canvas should look like as the program runs:


Problem B: One-dimensional Color Gradient

SPOILER ALERT: These next problems will requires some numerical calculations to get them right. You have been warned!

Write a p5.js sketch that draws this picture. The canvas is 250×450, and the circle diameter is 50.

One column of 9 circles going from black to red gradually

The color of the top circle is black (0, 0, 0) and the color of the bottom circle is pure red (256, 0, 0). The colors of the circles in between are shades of red that differ from each other by 32. The color of the 2nd circle down is (32, 0, 0). The color of the third circle down is (64, 0, 0), etc.

Write this without using a loop first. Then look for pattern(s) so you can replace the nine fill and circle functions with just one of each, with a surrounding for loop controlling the values for the fill and circle function calls. Comment out your original non-loop version and write your for loop version below it as your final version.


Problem C: Two-dimensional Color Gradient

Write a p5.js sketch that draws this picture. The canvas is 250×450, and the circle diameter is 50.

A grid of circles going from black to red gradually downward and black to green gradually to the right

The color of the top circle of the first column is black (0, 0, 0) and the color of the bottom circle of the first column is pure red (256, 0, 0). The color of the left circle of the first row is black (0, 0, 0) and the color of the right circle of the first row is pure green (0, 256, 0). The colors of the circles in between are shades of red and green combined. Down each column, the difference is 32 for red. Across each row,the difference is 64 for green. Note that the color of the circle in the bottom right should end up being pure yellow (256, 256, 0).

Start with a solution for problem B which controls red, and add a loop inside of your loop to form a nested loop. The inner loop will control green. Inside the inner loop, you will have the code to fill and draw each circle as a combination of red and green values.

(If this is confusing, you can do like the previous problem and write out the solution for problem B five times, changing each solution to draw the corresponding column. Then look for patterns to condense into nested loops. But this will take some time.)


Problem D: Generalized Gradient (challenging, if you have time)

Make a copy of your answer to exercise C into a new folder for problem D. Modify your program to make the following starting image (circle diameter and spacing is 10). Instead of just changing all of the numbers in your program, define a global variable (var size = 10; ) and see if you can remove all “magic numbers” (i.e. numbers that are tied to a specific spacing only) so that changing size will change the circle size and spacing.

A grid of smaller circles going from black to red gradually downward and black to green gradually to the right

Once you have this programmed, add the instruction size = mouseX / 5 + 10; as the last statement in the draw function (after the loops) and see if it works! If you’ve removed all of the “magic numbers”, then the grid of circles will scale larger or smaller as your mouse moves left and right with the color gradient adjusting to the number of circles drawn.

Note that if you move the mouse beyond the canvas, the circles continue to grow in size. Can you use the map function to limit the size of the circles?


Once you run out of time, you should submit your completed work for credit.