Is anyone here?

I'm here

but I can't answer your question, most likely. :)

do you knoe linear algebra?

ooh

I do know some yes

Oh :(

Oh good :)

I was expecting c# or some weird web technology

blog.wolfire.com/2010/07/… <----I was reading that

But then......

It got to the part about rotating the x and y axis

and?

looks like a pretty decent explanation. What part are you stuck on?

It said " The default axes are (1,0) for the x-axis and (0,1) for the y-axis, so we get the position 3(1,0) + 2(0,1). But the axes don't have to be (1,0) and (0,1)."

The part I'm stuck on: "To get the rotated x and y axes we just use the trigonometric function above. For example, if we are rotating by 49 degrees, then we get the new x-axis by rotating (1,0) by 49 degrees and we get the y-axis by rotating (0,1) by 49 degrees. Our new x-axis is (0.66, 0.75), and our new y-axis is (-0.75, 0.66)."

(1,0) is the unit X point

How can an axis have 2 axis?

if you rotate by an angle, it rotates into (cos(a), sin(a))

because it's a different coordinate system

okay. the left coordinate system we'll call (X,Y)

the axes are (x,y)

the right coordinate system, we can call (X', Y')

ok

X' is the slanted axis arrow

however, all those numbers on the right

are given in XY-space

if you represented them in X'Y'-space, the axes would still be (0,1) and (1,0)

and the triangle would still be (0,2), (-1,-1), and (1,-1)

Jimmy has it

the pink grid denotes X'Y' space

so your entire goal is to figure out howto convert between two different coordinate systems, one of which is rotated

Ok so my problem is how do I convert X'Y' to actual X Y

if you figure out that "if I rotate 49 degrees, the X' unit vector is at (0.66, 0.75) and the Y' unit vector is at (-0.75, 0.66)"

and so on

the X' unit vector will be at (cos(a),sin(a)) (if you don't understand this, you might want to review your trig book)

A trig book? I should buy one

knowledge of basic trig is essential for game programming.

usually actually having the book is unnecessary

I do know the basics

Like sin and cos

good :)

okay, the basics is probably enough

But I'm just having problems with this one thing

like, (1,0) rotates to (cos,sin) is basically the definition of sin/cos

As I said, how can one axis have two axes?

:(

think of it as a unit vector

not an axis

so you can represent the "X-axis" by the unit vector (1,0)

and the "Y-axis" by the vector (0,1)

A unit vector has a length (hypotenuse) of 1, right?

yes

so therefore, the X'-axis is simply a vector (0.66,0.75) in the same way

of course, these coordinates are in XY-space

in X'Y' space, the X'-axis is just (1,0) again

and it's the old X and Y axes that have funny values.

strictly speaking, (1, 0) is a unit vector that points in the X' direction. The X' axis itself is a line.

hmmm yes.

if you go back to the last illustration

take a red grid point and try to visualize where it falls on the blue grid

and vice versa, taking a blue grid point and visualize where it falls on the red grid

That's all you're doing when converting from one space to another

Is this how you convert?

Ignore the "point."

yes

at least for this example

Wait....that's wrong because in the picture, you have -0.75 and 0.75

usually we'd represent this in matrix notation

hold up

your notation is a bit backwards

since

what we're really saying is "(0,2) in X'Y' space" and we need the XY-space coordinates

be right back

I put out a game kongregate.com/games/EscalationStudio/splode

Diggin' the art.

Back!

Though I'm getting a little sea-sick from the rocking...

Tetrad: could you help me with this linear algebra?

You know what, I'll figure this out some other time thanks to everyone who helped me so far.

@AidanMueller What exactly are you trying to do?

@Tetrad Very nice! My only (minor) complaint is that the Splodes are cute, and I don't like popping them. :(

gotta shut down for software installation. back later

Using Bresenham to draw lines in OpenGL. What? :)

"Let's do this in the most complicated way possible." xD

There are legitimate reasons to do it that way

otherwise: ouch