Move 360 degrees and maintain angle?

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Crabbages

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Posted: 9th Mar 2012 23:23

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Hey guys! Wonder if you can point me in the right direction.

I had used 'setspriteoffset' and 'setspriteangle' to have my sprites rotate around a certain point. I've been trying to have sprites stay upright while moving in a circle, but because only the angle changes and not the X or Y position I'm not able to have the sprite keep its current position AND face upright.

I thought of animating the image to turn the opposite way...but that seems a bit drastic.

Can anyone tell me what I should be doing instead?

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Hodgey

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Posted: 9th Mar 2012 23:47

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Quote: "I'm not able to have the sprite keep its current position AND face upright.
"

You might need some trigonometry here. I wrote a few functions for the UCF project (see sticky on this board) to simplify the process though.

A small example (project attached as well):

+ Code Snippet

rem
rem AGK Application
rem
SetVirtualResolution(GetDeviceWidth(), GetDeviceHeight())
Spr = CreateSprite(LoadImage("Char0001.png"))

X as float = 200.0
Y as float = 150.0
Angle as float
Vel as float = 2.0

rem Hodgey Did It!
do
    // increase the angle
    Angle = Angle + 1.0
    if Angle > 360.0 then angle = 0.0

    // reposition the sprite
    X = NewXValue(X, Angle, Vel)
    Y = NewYValue(Y, Angle, Vel)
    SetSpritePosition(spr, x, y)

    // sync
    Sync()
loop

Function NewXValue( X#, Angle#, Speed#)
    X# = X# + (cos(Angle#) * Speed#)
Endfunction X#

Function NewYValue( Y#, Angle#, Speed#)
    Y# = Y# + (sin(Angle#) * Speed#)
Endfunction Y#

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Crabbages

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Posted: 10th Mar 2012 02:20

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Hey Hodgey, I couldn't work out how to set the speed.

Vel = distance to centre of circle? (could the centre be set as a coordinate?)

I increased the Vel and that made the circle larger.
I increased the angle to make it go faster but that made the circle smaller(and without correcting every 360, my sprite eventually flew away to the right).

So, it did work for rotating! Thankyou!
but I'd also need control of the speed at which the sprite travels.

I'll continue to play around though, then maybe look into the dreaded land of trigonometry... see what comes up and report back!

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Hodgey

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Posted: 10th Mar 2012 11:33 Edited at: 10th Mar 2012 11:33

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Quote: "Hey Hodgey, I couldn't work out how to set the speed.

Vel = distance to centre of circle? (could the centre be set as a coordinate?)"

Yeah, the functions actually aren't really designed for orbiting, my bad. But there is a solution.

Try these:

+ Code Snippet

Function OrbitXValue( CenterX#, Angle#, Distance#)
    X# = CenterX# + (cos(Angle#) * Distance#)
Endfunction X#

Function OrbitYValue( CenterY#, Angle#, Distance#)
    Y# = CenterY# + (sin(Angle#) * Distance#)
Endfunction Y#

Replace the New xy value functions with those. I haven't actually tested them as it's late over here but they should work. Here's a nice explanation of the maths if the functions don't work and/or you get stuck.

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baxslash

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Posted: 10th Mar 2012 13:18

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Watch out for the aspect ratio problem if you're using aspect based display.

You might need to divide or multiply one of those values by "getAspectRatio()" to get a none eliptical orbit.

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Crabbages

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Posted: 10th Mar 2012 22:59

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Heyyyy yooooou guuuuuys!

Theres a nice little page on using sin and cos here...
http://www.helixsoft.nl/articles/circle/sincos.htm

From editing his example of drawing dots to make up a circle andremembering what you guys said I got this...

+ Code Snippet

X as float = 50.0
Y as float = 50.0
Length as float = 20.0
angle as float = 0.0
anglestep as float = 0.4
screenh as float
screenw as float

DO
        X = Length* cos(angle)
        Y = Length* sin(angle)
        screenh = getvirtualheight()
        screenw = getvirtualwidth()
        setspriteposition(sprite1,X+screenw/2,Y+screenh/2)
        angle = angle + anglestep
    Sync()
LOOP

remstart
The X and Y defines the middle point of orbit. 
Length is the distance the sprite is away from that point.
anglestep is the speed.
remend

Now don't question any of this because I'm afraid it will fall to pieces.

What do you think?

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Hodgey

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Posted: 10th Mar 2012 23:28

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Quote: "What do you think? "

The important thing is if you understand what it's doing.

Quote: "The X and Y defines the middle point of orbit. "

Not quite. The X and Y is where abouts the sprite would be in the circular movement according to the angle. The middle point, according to your code snippet, is what's added to x and y. So in this case, Screenw/2 and Screenh/2 is the middle point.

Quote: "Length is the distance the sprite is away from that point."

That's correct.

The final thing you need to do in your snippet is to actually create the sprite.

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