Choosing a 3d (space) movement system

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Devonps

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Posted: 26th Feb 2010 19:34

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I would like to create a single player 3D based space shoot-em up and was unsure of which of movement system to use for the players ship, for example: Free flight or Euler based.

Can people comment on which will be easier for me to code?

I would rate my game coding skills as a beginner.

I\'d prefer links to articles so I can learn the answers for myself - but explanations are just as good.

Thanks in advance,
Steve.

Marriage is a circle of rings....
Engagement ring, Wedding ring, Suffering!

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KISTech

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Posted: 27th Feb 2010 18:47 Edited at: 27th Feb 2010 18:48

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I've gone back and forth between just using the 0 to 360 degree angles that DBPro functions give you, and the results that EZRotate gives you for about 3 years now.

I've actually settled on using the values that DBPro gives you. EZRotate has some good uses, but it's easy to get things turned around in the wrong direction.

If you aren't planning on limiting the users movement in some way on at least one axis, then your biggest hurdle will be overcoming gimbal lock. Aside from that it's just simple rotation using degrees.

Gimbal Lock on Wikipedia.org
http://en.wikipedia.org/wiki/Gimbal_lock

This math site has potential to help if you really want to get into the deep dark depths of the math.
http://www.euclideanspace.com/maths/geometry/transform/index.htm

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Zotoaster

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Posted: 27th Feb 2010 19:35

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The thing about DBPro's rotation system is that it's unrealistic in a space scenario. As you probably know, there is no "up" in space, but with DBPro's rotation there is, because all Y rotations are done on the global Y axis. However, not all the rotations are global. X rotations are done on the local X axis.

Free flight is probably best in this case. You won't end up with any gimbal lock doing so anyway. However, it will be problematic to read off angles from the ship, to know in which direction to shoot missiles etc. In this case some matrix math would be really useful, and I've never used DBPro's matrix math commands.

"everyone forgets a semi-colon sometimes." - Phaelax

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Indicium

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Posted: 27th Feb 2010 23:06

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Quote: "The thing about DBPro's rotation system is that it's unrealistic in a space scenario. As you probably know, there is no "up" in space, but with DBPro's rotation there is, because all Y rotations are done on the global Y axis. However, not all the rotations are global. X rotations are done on the local X axis."

Could you explain that please? I don't understand the difference between a local axis and a global axis.

Windows Vista 32-Bit Home Premium Intel Pentium Dual-Core @ 1.46Ghz 2038mb RAM

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Zotoaster

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Posted: 28th Feb 2010 12:13

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Well a global axis doesn't change with the rotation of any object, it always stays the same. A local axis does change though, so, for instance, if you're in a car, 'up' for you is always going to be the direction that the ground is facing, even if you end up upside-down somehow.

A local axis changes with your orientation, which is what space is like. If you're in space, it doesn't matter how you rotate your ship - 'up' is always going to be the direction that the top of your head points to.

Gettit?

"everyone forgets a semi-colon sometimes." - Phaelax

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Devonps

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Posted: 28th Feb 2010 12:51

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@Kistech - thanks for the links, the Screw Theory made sense!

@Zotaster - thanks for the extra information.

So far I've managed to rotate my model in 3D with the following code

do

rem x/y/z rotate the object
rem
rem some notes to remember
rem 
rem WRAPVALUE - This command will return a value(float) that does not exceed the range of 0 to 360

rem get movememt
	if keystate(44)=1  rem w pressed --> makes the ship roll clockwise
		yang = yang + 5
	endif
	if keystate(30)=1 rem a pressed --> makes the ship pitch down
		xang = xang + 5
	endif
	if keystate(45)=1 rem s pressed --> makes the ship roll anti-clockwise
		yang = yang - 5
	endif
	if keystate(32)=1 rem d pressed --> makes the ship pitch up
		xang = xang - 5
	endif	
	
	if keystate(17)=1 rem z pressed --> makes the ship turn anti-clockwise
		zang = zang + 5
	endif
	
	if keystate(31)=1 rem x pressed --> makes the ship turn clockwise
		zang = zang - 5
	endif
	
rem	xrotate object 1,xang
rem	yrotate object 1,yang
rem	zrotate object 1,zang
	
	rotate object 1, xang,yang,zang
	
	position object 1,objx,objy,objz	
	position camera 0,camx,camy,camz

text 0,0, "W/S = roll  A/D = pitch Z/X = turn"
text 0,10, "Cam X:" + str$(camx)
text 0,20, "Cam Y:" + str$(camy)
text 0,30, "Cam Z:" + str$(camz)
text 0,40, "Angle X:" + str$(wrapvalue(object angle x(1)))
text 0,50, "Angle Y:" + str$(wrapvalue(object angle y(1)))
text 0,60, "Angle Z:" + str$(wrapvalue(object angle z(1)))
	sync
loop

+ Code Snippet

do

rem x/y/z rotate the object
rem
rem some notes to remember
rem 
rem WRAPVALUE - This command will return a value(float) that does not exceed the range of 0 to 360

	rem get movememt
	if keystate(44)=1  rem w pressed --> makes the ship roll clockwise
		yang = yang + 5
	endif
	if keystate(30)=1 rem a pressed --> makes the ship pitch down
		xang = xang + 5
	endif
	if keystate(45)=1 rem s pressed --> makes the ship roll anti-clockwise
		yang = yang - 5
	endif
	if keystate(32)=1 rem d pressed --> makes the ship pitch up
		xang = xang - 5
	endif	
	
	if keystate(17)=1 rem z pressed --> makes the ship turn anti-clockwise
		zang = zang + 5
	endif
	
	if keystate(31)=1 rem x pressed --> makes the ship turn clockwise
		zang = zang - 5
	endif
	
rem	xrotate object 1,xang
rem	yrotate object 1,yang
rem	zrotate object 1,zang
	
	rotate object 1, xang,yang,zang
	
	position object 1,objx,objy,objz	
	position camera 0,camx,camy,camz	

text 0,0, "W/S = roll  A/D = pitch Z/X = turn"
text 0,10, "Cam X:" + str$(camx)
text 0,20, "Cam Y:" + str$(camy)
text 0,30, "Cam Z:" + str$(camz)
text 0,40, "Angle X:" + str$(wrapvalue(object angle x(1)))
text 0,50, "Angle Y:" + str$(wrapvalue(object angle y(1)))
text 0,60, "Angle Z:" + str$(wrapvalue(object angle z(1)))
	sync
loop

My next step is to simulate the movement through space and around a 2nd object.

Regards,

Steve.

Marriage is a circle of rings....
Engagement ring, Wedding ring, Suffering!

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KISTech

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Posted: 28th Feb 2010 17:33

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That code will work, but as Zotoaster mentioned, your turns on the Y axis will be on the Global Y. That's where some of that extra math might come in handy. If turning on the Global Y is acceptable for your purposes then you're all set. (I'm doing that for my game too. It's just easier, and the players are less likely to get disoriented.)

Quote: "However, it will be problematic to read off angles from the ship"

The object angle commands just return the global angles of the ship. So no matter what methods you're using to achieve the rotations you want, the object angle commands will give you the proper global angles of the object.

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Zotoaster

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Posted: 28th Feb 2010 18:46

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Ah, yes, you are correct. My bad.

"everyone forgets a semi-colon sometimes." - Phaelax

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Devonps

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Posted: 2nd Mar 2010 21:10 Edited at: 2nd Mar 2010 23:12

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Thanks for the help guys, I've managed to move my spaceship based on the direction it's facing

I've posted my updated code for others to maybe learn from

I've added extra keys to control the ships velocity (increase/decrease) and a key to bring the ship to a dead stop.

vel# = 0.2
do

rem get movememt
	if keystate(17)=1  rem w pressed --> makes the ship roll clockwise
		xang = xang + 5
	endif
	if keystate(30)=1 rem a pressed --> makes the ship pitch down
		yang = yang + 5
	endif
	if keystate(31)=1 rem s pressed --> makes the ship roll anti-clockwise
		xang = xang - 5
	endif
	if keystate(32)=1 rem d pressed --> makes the ship pitch up
		yang = yang - 5
	endif	
	
	if keystate(44)=1 rem z pressed --> makes the ship turn anti-clockwise
	zang = zang + 5

endif
	
	if keystate(45)=1 rem x pressed --> makes the ship turn clockwise
	zang = zang - 5	
	endif
rem ship velocity	
	if keystate(51) = 1 rem , pressed --> this provides velocity to move the ship
		vel# = vel# + 0.2
	endif
	
	if keystate(52) = 1 rem . pressed --> this provides velocity to move the ship
		vel# = vel# - 0.2
	endif
	
	if keystate(57) = 1 rem space bar pressed --> this stops the ship dead!
		vel# = 0
	endif

if wrapvalue(object angle x(1)) < 55 then xang = 55
if wrapvalue(object angle x(1)) > 340 then xang = 340

rotate object 1, xang,yang,zang
		move object 1,vel#

position camera 0,object position x(1),object position y(1)+10,object position z(1)	-50
	
text 0,0, "W/S = roll  A/D = pitch Z/X = turn  ,/. inc/dec velocity space=all stop"
text 0,10, "Cam X:" + str$(camx)
text 0,20, "Cam Y:" + str$(camy)
text 0,30, "Cam Z:" + str$(camz)
text 0,40, "Angle X:" + str$(wrapvalue(object angle x(1)))
text 0,50, "Angle Y:" + str$(wrapvalue(object angle y(1)))
text 0,60, "Angle Z:" + str$(wrapvalue(object angle z(1)))
text 0,70, "XANG:" + str$(xang)
text 0,80, "YANG:" + str$(yang)
text 0,90, "ZANG:" + str$(zang)
text 0,100, "Speed:" + str$(vel#)
	sync
loop

+ Code Snippet

vel# = 0.2
do

	rem get movememt
	if keystate(17)=1  rem w pressed --> makes the ship roll clockwise
		xang = xang + 5
	endif
	if keystate(30)=1 rem a pressed --> makes the ship pitch down
		yang = yang + 5
	endif
	if keystate(31)=1 rem s pressed --> makes the ship roll anti-clockwise
		xang = xang - 5
	endif
	if keystate(32)=1 rem d pressed --> makes the ship pitch up
		yang = yang - 5
	endif	
	
	if keystate(44)=1 rem z pressed --> makes the ship turn anti-clockwise
	zang = zang + 5

	endif
	
	if keystate(45)=1 rem x pressed --> makes the ship turn clockwise
	zang = zang - 5	
	endif
rem ship velocity	
	if keystate(51) = 1 rem , pressed --> this provides velocity to move the ship
		vel# = vel# + 0.2
	endif
	
	if keystate(52) = 1 rem . pressed --> this provides velocity to move the ship
		vel# = vel# - 0.2
	endif
	
	if keystate(57) = 1 rem space bar pressed --> this stops the ship dead!
		vel# = 0
	endif

if wrapvalue(object angle x(1)) < 55 then xang = 55
if wrapvalue(object angle x(1)) > 340 then xang = 340


rotate object 1, xang,yang,zang
		move object 1,vel#	

position camera 0,object position x(1),object position y(1)+10,object position z(1)	-50
	
text 0,0, "W/S = roll  A/D = pitch Z/X = turn  ,/. inc/dec velocity space=all stop"
text 0,10, "Cam X:" + str$(camx)
text 0,20, "Cam Y:" + str$(camy)
text 0,30, "Cam Z:" + str$(camz)
text 0,40, "Angle X:" + str$(wrapvalue(object angle x(1)))
text 0,50, "Angle Y:" + str$(wrapvalue(object angle y(1)))
text 0,60, "Angle Z:" + str$(wrapvalue(object angle z(1)))
text 0,70, "XANG:" + str$(xang)
text 0,80, "YANG:" + str$(yang)
text 0,90, "ZANG:" + str$(zang)
text 0,100, "Speed:" + str$(vel#)
	sync
loop

What I need to do next is add some code to restrict the ship rotation in all 3 angles.

Edited: As I noticed I had the keystates & angles the wrong way round - doh!

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Engagement ring, Wedding ring, Suffering!

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feiting shadow

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Posted: 19th Mar 2010 08:26

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zotoaster, you can avoid matrix math using DBP's built-in commands.

Set object to object orientation.
Move object.

And likewise with the camera. Then you simply initiate the movement.

If you wish to do free flight of the missiles without using move object, only use move object initially to find the displacement.

Eg.
Get X,Y,Z
Move object 10
get x y z
Move object back (-10)
Set object x velocity to (New X minus old X)
Do same for Y and Z
Store the X,Y,and Z velocities in a separate variable.

In your main game loop, add an update() that alters the physics to those specifications.

I avoided using sin and cos and made realistic flight doing this, but my HD crashed before I posted.

You can always reference my code under WIP to see how I handle objects. Remember there's a tutorial on using my already-made engine. (3d space engine dbp)

I got bored before adding collisions, so it is not complete for this, but still workable.

Also, I rarely come here (until school ends at least), so don't rely on me returning anytime soon. Sorry.

fs

Signed
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