Author Topic: Tangent?  (Read 9371 times)

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Offline BlakPilar

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Tangent?
« on: May 07, 2012, 08:02:03 pm »
Is there a way tangent could be implemented? I've tried sin/cos, but I always get something really small, usually 0, 1, or 2 (I think). I'm making a shooter that has angled bullets for shiggles because I have nothing to do in my pre-calc class now that it's AP season (my tests are towards the end), and right now I just use a sort of slope method, but I figured it might possibly be easier/better in some way to use an angle. Then again, I've been wrong before ^^

Offline Happybobjr

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Re: Tangent?
« Reply #1 on: May 07, 2012, 08:08:18 pm »
Could you give us a sample please?
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Re: Tangent?
« Reply #2 on: May 07, 2012, 08:12:27 pm »
Xspeed = cos(θ) * speed
Yspeed = sin(θ) * speed

That should get the job done right?
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Offline BlakPilar

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Re: Tangent?
« Reply #3 on: May 07, 2012, 08:45:15 pm »
Basically what I have is all of my bullets' data stored in L1, with the format being this:

Offset | Meaning
n+0    | ^r = X
n+2    | ^r = Y
n+4    | Slope
n+5    | Flag for up/down


Now, I do realize I don't need the word-sized X and Y, but I didn't feel like working with one-byte variable numbers while I was writing this. Anywho, basically what id does right now is at every update the X is incremented by 1 and if X^slope is zero, I change Y based on the flag. Right now it works fine, but my question was instead of doing a slope, would it be easier to have something like tangent be used to calculate an angle? (I just remembered it's arctan(Y/X) = angle, not the other way around >.<)
« Last Edit: May 07, 2012, 08:45:33 pm by BlakPilar »

Offline Builderboy

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Re: Tangent?
« Reply #4 on: May 07, 2012, 09:30:55 pm »
Instead of using slope and a flag, would it not be easier to use just an angle instead?  That way you can specify the full range of directions in equal precision, and it would take up less data and use already implemented Axe commands.  Your slope would range from 0 to 256, where 0 is directly to the right, 64 is directly down, 128 is directly to the left, and 192 is directly up.  To extract the directions from the angle, simply use Cos(angle) for the X direction and Sin(angle) for the Y direction

Offline BlakPilar

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Re: Tangent?
« Reply #5 on: May 07, 2012, 09:33:20 pm »
Instead of using slope and a flag, would it not be easier to use just an angle instead?

Precisely my initial question lol. But I don't need to worry about left/right movement. The bullets start on the left side of the screen in the middle, and are fired so they go to the right either up or down.

Offline Builderboy

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Re: Tangent?
« Reply #6 on: May 07, 2012, 10:31:47 pm »
Well using an angle method still works well, and if this is for some sort of shooter game, that means you can re-use some code for any bullets that are being fired back at you :D

Offline Wretchedlout

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Re: Tangent?
« Reply #7 on: May 07, 2012, 10:48:34 pm »
Couldn't you derive it?

Offline Builderboy

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Re: Tangent?
« Reply #8 on: May 07, 2012, 11:09:01 pm »
Derive what?

Offline cooliojazz

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Re: Tangent?
« Reply #9 on: May 07, 2012, 11:15:21 pm »
Tangent as in the trigonometric function, not the slope of a line at a point =P  So, no there is nothing useful to derive here...
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Re: Tangent?
« Reply #10 on: May 08, 2012, 05:57:02 am »
Yeah I would pretty much like a tan( function.
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Offline calc84maniac

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Re: Tangent?
« Reply #11 on: May 08, 2012, 09:42:24 am »
I feel like this would work:
Code: [Select]
Lbl Tan
Return sin(r1)*256//cos(r1)
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Re: Tangent?
« Reply #12 on: May 16, 2012, 10:56:55 pm »
Why *256? tan(angle) is defined as y/x, and with sin(angle) and cos(angle) being y/r and x/r respectively, tan(angle) can also be defined as sin(angle)/cos(angle), so i dont see why you would multiply sin(angle) by 256 first.

Offline Hayleia

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Re: Tangent?
« Reply #13 on: May 17, 2012, 02:40:27 am »
Why *256? tan(angle) is defined as y/x, and with sin(angle) and cos(angle) being y/r and x/r respectively, tan(angle) can also be defined as sin(angle)/cos(angle), so i dont see why you would multiply sin(angle) by 256 first.
Else you would lose precision, as the division in Axe doesn't care about the remainder. For example, 7/2=3.5 but in Axe, 7/2=3 (if you don't do floating point math of course ;))
This is also why cos and sin return between -127 and 127 because if it returned between -1 and 1, it would always be 0
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Re: Tangent?
« Reply #14 on: May 17, 2012, 03:58:23 pm »
But multiplying by 256 just changes it from something like $00A6 to $A600. It doesnt increase precision, but just changes the value. sin($A600) is completely different than sin($00A6).