EBoard 04: RGB Colors (Section 3)

Warning! You are being recorded (and transcribed) (provided the technology is working correctly).

You should know the start-of-class algorithm

Please return your card to the jar after you grab it.

Approximate overview

• Administrative stuff
• Q&A from readings
• Lab
• Quiz

Administrative stuff

Introductory Notes

• Scamper is now on version 4.3.0. Make sure that’s the version you’re running. If not, reload.
• We’re all getting used to the Scamper environment (including me).
  • There will be some unexpected infelicities.
  • Don’t worry, it will get smoother and more natural.
  • The developers are happy to make changes, so let me know what changes you’d like to see.
• Some of you struggled to figure out how to rotate one of the triangles. Note that there’s a help system in scamper.
  • Sam demos
• I finally remembered to release the grades on reading responses (for today’s reading; the others are forthcoming).
• When you book meetings, I’d prefer that you book 15-minute sessions rather than 30-minute session.
• Monday is labor day, where we celebrate the wonder of unions and working people. There is no class.

Upcoming activities

Scholarly

• Thursday, 10 September 2026, 11:00 a.m.–noon, JRC 101. Scholar’s Convocation: Ruth Feingold
• Thursday, 10 September 2026, 4:00–5:00 p.m., JRC 101. The Department of Revenge (NY Times Reporter)

Artistic/Cultural

Multicultural

• Friday, 4 September 2026, 4:10–5:00 p.m., HSSC N1170. Middle of Everywhere (Algeria)
• Tuesday, 8 September 2026, Black Cultural Center (10th and Park). BCC Bridge: First Year Connections

Peer

Musical, theatric, sporting, academic, and similar events involving this section’s students are welcome.

• Saturday, 5 September 2026, 1:00 p.m.–4:00 p.m., Rosenbloom Field Men’s American Football vs. Mount Mercy

Wellness

• Monday, 7 September 2026, 6:30–8:00 p.m., Bear Dance Studio. Brazilian Jiu-Jitsu
• Monday, 7 September 2026, 8:00–9:00 p.m., Prayer Garage. Meditation Group
• Tuesday, 8 September 2026, 4:30–6:00 p.m., Bear P103. Wellness Yoga
• Tuesday, 8 September 2026, 5:00–8:00 p.m., HSSC North Atrium. Therapy Dogs
• Wednesday, 9 September 2026, 6:30–8:00 p.m., Bear Dance Studio. Brazilian Jiu-Jitsu

Misc

• Wednesday, 9 September 2026, 8:00 p.m.–9:00 p.m., Noyce 3rd. Mentor Session
• Thursday, 10 September 2026, 8:00 p.m.–9:00 p.m., Noyce 3rd. Mentor Session

Other good things

These do not earn tokens, but are worth your consideration.

• Friday, 4 September 2026, 7:00–9:00 p.m., Darby. Volleyball vs St. Benedict (UPDATED)
• Saturday, 5 September 2026, 11:00 a.m.–1:00 p.m., Darby. Volleyball vs. St. Catherine
• Saturday, 5 September 2026, 1:00–3:00 p.m., Springer Field. Men’s Unamerican Football vs. Hamline
• Saturday, 5 September 2026, 3:00–5:00 p.m., Darby. Volleyball vs. Simpson College
• Sunday, 6 September 2026, 11:00 a.m.–1:00 p.m., Springer Field. Women’s Unamerican Football vs. St. Mary’s
• Wednesday, 9 September 2026, 4:30–6:00 p.m., Springer Field. Women’s Unamerican Football vs. Coe
• Saturday, 12 September 2026, Grinnell Track. Les Duke Invitational (Cross Country)

Upcoming work

• Due Tuesday, 2026-09-08:
  • Today’s lab
    • RGB colors
    • Submit what you have at the end of class.
  • Reading responses
    • Computation via expressions
  • Mental models of computation
• On Friday, 2026-09-11:
  • Quiz/LA on tracing (next Wednesday’s class).
  • REDO Quiz/LA on decomposition.
  • REDO Quiz/LA on procedures.

Administrative Q&A

Can I get a token for attending event?

Tokens are only available for the events I mention in class (or on Teams).

If you think an event falls within the broad guidelines, suggest it to me (preferably before class) and I’ll add it if I agree.

Friday PSA

• Don’t feel like you have to do what others are doing (or seem to want you to do). Decide what’s right for you.
• People care about you, so please take care of yourself, if not for you, then for them.
• Moderation!
• Consent is essential. (Consent is also difficult/impossible to assess if either party is impaired.)

Q&A from Readings

Will we be tested on the terminology in the reading Design & Color?

No.

What would LAs look like for problems related to color?

Color is not an explicit LA topic. Colors will only be used as part of other topics.

Can we go over remove-blue?

Sure.

Can I have two functions with the same name and a different number of parameters?

No. Not in Scheme. (Yes in Java.)

How do you make optional parameters?

For now, you don’t.

I’m not sure in Scamper.

What is an alpha value?

The alpha value is transparency/opacity.

We’ll explore this by overlaying different opacities of red on blue.

    (overlay (solid-circle 100 (rgb 255 0 0 255))
             (solid-square 100 (rgb 0 0 255)))
    (overlay (solid-circle 100 (rgb 255 0 0 192))
             (solid-square 100 (rgb 0 0 255)))
    (overlay (solid-circle 100 (rgb 255 0 0 128))
             (solid-square 100 (rgb 0 0 255)))
    (overlay (solid-circle 100 (rgb 255 0 0 64))
             (solid-square 100 (rgb 0 0 255)))
    (overlay (solid-circle 100 (rgb 255 0 0 0))
             (solid-square 100 (rgb 0 0 255)))

What happens if we don’t add the alpha in creating an RGB color?

255 is the default.

Lab

If you finish early, do some of the extra problems.

It’s also okay if you don’t finish! Since today is a short class, you probably won’t finish.

At the end, follow the “end of lab” algorithm.

• Save the file to disk.
• Upload it to Gradescope
• Wait for the autograder. (Today’s just says it ran; future ones will say more.)
• Email it to your partner.

Quiz

If you finish early, you can leave. Have a great weekend!

At 4pm, you should stop unless you are very close to finishing.