lamberta / html5-animation Goto Github PK

The code for the 04-wave-1.html in the book is missing the line

angle+= yspeed;

So the ball does not move vertically.

Hello,

Your book is excellent, Thank You for writing it.
Books like yours have been my source of education for web development.

I just noticed a small thing on page 63 of the pdf file and thought I would bring it to your attention.

"Breaking that down, you get 36 + 64, or 100 = dist**2.

With some basic algebra, you can reduce that to .100 = dist.
/* I believe this sentence should be omitted */

And from that, you can easily figure out that the distance between the two objects is 10."

Thank You again for your work.

Jim

Hi Billy, great book.

On page 228, there's a couple of equations

x1 = (x-centerX) * cos(rotation) - (y-centerY) * sin(rotation)
y1 = (y-centerY) * cos(rotation) + (x-centerX) * sin(rotation)

I tried coding these up and it certainly rotates the point, but it is offset by (-centerX, -centerY)

Should the equations be these?

x1 = centerX + [(x-centerX) * cos(rotation) - (y-centerY) * sin(rotation)]
y1 = centerY + [(y-centerY) * cos(rotation) + (x-centerX) * sin(rotation)]

Cheers,

Ed

nice works.

Ben Joff, 2006

[This question was sent to me via email, excerpts reposted here with permission.]

I have been playing with the code below [Chapter 8, Example 11] ... When the canvas renders the lines, they're on top of the balls, but in the example before (where an array is not used) the balls are drawn on top. I was trying to figure out how to draw the line underneath like the first example. Going through the code I am not sure where ballB gets defined. var ballA = balls[i-1]; defines ballA but how is ballB defined? Is it a key from the array? And if so why is ballA defined?
Thank you!
Peter