MMF math

[arfa]

I am working on a parabola trajectory setup and could do with some MMF-style math help.

Plotting X,Y of an object path is done. I have a nice, time controlled (as opposed to frame rate) flight.
I would like to be able to calc the angle of the object to set its angle.

My approach is to set variables X1, Y1 then, a 1/100th later, X2, Y2.
Angle = A
tanA = opposite/adjacent = (X2-X1)/(Y2-Y1)

So, how to get the angle? Or is there a better way?

EDIT_______
Poking around a few math forums/sites it seems I am looking for inverseTan. Beats me if I can find an actual formula that converts the ratio to an angle.

[Dynasoft]

Use atan2(). It takes the x and y (aka opposite and adjacent) and does an inverse tan with quadrant correction to get the original angle.

[Jax]

Just use aTan2.

Was my example in the other thread any use to you?

[arfa]

Thanks Jax.
>> my example in the other thread...
I missed that. Just downloaded and will study after lunch. Thanks.

Thanks Dynasoft
This looks promising but does not smooth my furrowed brow

Where in the expression editor do I get "atan2()"? Or, what is the actual arrangement of X, Y?

[Dynasoft]

Either type it, or it's in retrieve data of the special object somewhere. You need a recent build, it was added in b248.

The use is apparently: atan2(y2-y1, x1-x2)

[arfa]

Yes, special object > arc tangent y/x
the use is indeed: atan2(y2-y1, x1-x2)

The current game I am building was started in an earlier version and I have noticed some things that are 'different' in my recent upgrade. So, I am playing it safe - which means I don't have atan2 available.

I am also curious about the math behind the calculation. So, my quest continues.

[Dynasoft]

atan2() is just a version of atan() (the inverse tan function) which corrects for an x of 0 (causes a div/0 error normally, instead of being +/- 90 degrees) and looks for a negative x to support angles past +/-90 (atan falsely registers y/-x as being -y/x instead).

[arfa]

OK - I see that my old version has atan() lurking in the same location. I will try that.

As to your other comments... WAY over my head - certainly on first read. I won't be using/allowing angles over 90 so imagine it will function well enough.

Thanks for leading me on. I have been away from MMF for about a decade and am slowly getting up to speed with all the new functions.

@Jax
That works really well. I like the keyed adjustment - although I may have to give thought to player conflict. I am using standard trajectory formula:
x = vt cosA
y = vt sinA - ½ g t²
I am planning a trace follower, or rocket fire and such and like being able to plot x/y along the way.

Yours is simpler. Thanks.

[arfa]

The current hitch is setting X1/Y1,X2/Y2 to calc the angle.

on press enter > set x1/y1 then
every 12" > calc angle using ATan with x2/y2 then
every 12" set x1 = x2, y1 = y2

My thought is that the calc for the angle would be done first but this doesn't seem to be the case.

Is there an easy way to store the position values for previous position?

I am experimenting with setting a 'trace' dot and using its position but so far no luck.

I am moving slowly ahead with this and will post a final example. I found a 'bullet widget' that works fine but this is a great learning exercise for me.
Thanks for your help. ~AK

[arfa]

Bumping a bit here but i thought you might like to see my working example.

http://www.buddhamind.info/mmf/AK_parabola-3.mfa

The only thing I am thinking to add is a tracer behind the projectile. A line of fading dots that follow the parabola.

This has been quite project for me. A great way to learn.