(no subject)

Sunday, August 14th, 2011 14:30
I just wrote up a couple tips for debugging simple physics simulations (of the sort you use in 2D games), in a bit more detail than the context required.

I've written a new topic index page for my site: Games, simulations, and animations. Except for the note about Tile Game, everything on it is something I've already published.

Condensed list of the contents: Tile Game, Fire Worms, Mouse-maze, 15-puzzle, screen savers, Varychase, Linkage, Bouncyworm, Brownian Tree, pendulum animation.

(no subject)

Monday, October 4th, 2010 18:39
x {UleavesTair,avg}d x 0     when t now (mod 1 solar year)

(no subject)

Monday, April 26th, 2010 09:32

(Images are public domain from Wikimedia Commons: 1 2)

2000 food calories/day ≈ 100 watts

Normal People Things:

  • Gone to a party unrelated to my family.

Never thought I'd do:

  • Worn a t-shirt with text on it.
  • Written an essay structured using a gratuitous extended metaphor.

Extra nerd points:

  • Programmed a number type which carries units and error values, to reduce the tedium of lab reports.
  • Learned to write all my assignments in LATEX.

I used to wonder why color LCD displays always have backlights (and when the light is off they're very dark). I haven't actually researched the matter, but I recently thought of a highly plausible explanation:

A LCD per se is just a device which either blocks or transmits light under electrical control. A simple monochrome LCD (as in a digital watch) just has a reflective back panel; so the opaque segments are dark and the transparent ones pass the ambient light in both directions. If there's a backlight, then the light from it goes through the LCD in one direction.

A color LCD simply adds red, green, and blue filters aligned with the LCD elements, filtering the white backlight.

So, an ambient-light color LCD will be throwing away at least 2/3 of the light hitting it, because for any given red element, the filter is throwing away all the green/blue light, and similarly for the other colors. Therefore a reflective LCD displaying pure "white" can only achieve dark gray (compared to ordinary white objects which reflect nearly all of the light hitting them). Furthermore, the ambient light is not going to be coming in perfectly perpendicular, but from all directions — so it won't necessarily arrive through the same color filter as it departs through, leading to further losses.

I get the feeling the textbook writers had a list of everyday objects which they randomly picked from to avoid saying “an object” in each exercise. The results are mostly just distracting or mildly amusing, but sometimes they're a bit too much:

Sample Problem 9-6One-dimensional explosion: A ballot box with mass m = 6.0 kg slides with speed v = 4.0 m/s across a frictionless floor in the positive direction of an x axis. The box explodes into two pieces. One piece, with mass m_1 = 2.0 kg, moves in the positive direction of the x axis at v_1 = 8.0 m/s. What is the velocity of the second piece, with mass m_2?

— Halliday, Resnick, Walker, Fundamentals of Physics, 8th ed., page 215

Having repeatedly heard the “they tried to evolve an oscillator in a FPGA, but got a radio instead” story, I was glad to encounter (via Making Light) a link to the original paper, “The Evolved Radio and its Implications for Modelling the Evolution of Novel Sensors”.