Obtaining Positional Data

[betancourtb82]

Earilier in this forum, when we discussed the crosshair, you mentioned that we shouldn't be using objects that are attached to the screen when using stereo. I spoke to Mattias this weekend at the VR conference in Alexandria, VA and he mentioned that if we use a 3d object, we would probably be able to fix the problem of the bullets (mentioned in above posts) without having to change the IPD. Is this the case. Is there some way of making a "3d crosshair" that will accurately point to where the bullet would go? If so, do you have any ideas on how this can be implemented? I was thinking of making a vector that would match the vector of the bullet and place an icon (crosshair) at some point on the vector, in 3d, to show an aiming point. How does this idea sound? Can it be done? Please help.

Below is the code I have for the bullet so far.

def shootBullet():
	global nextBullet
	#find the next available ball to shoot
	bullet = bullets[nextBullet]
	nextBullet = (nextBullet + 1) % NUM_BULLETS
	#Calculate the vector of the ball based on the mouse position
	pos = viz.mousepos()
	bulletvector = viz.screentoworld(pos[0]+0.25,pos[1]) #Need to account for stereo
	bullet.vector = viz.Vector(bulletvector[3]-bulletvector[0],bulletvector[4]-bulletvector[1],bulletvector[5]-bulletvector[2])
	bullet.vector.normalize()
	bullet.vector *= BULLET_SPEED
	
	#translate the bullet to the head position
	bullet.translate(viz.get(viz.HEAD_POS))
	
	#make the bullet visible
	bullet.visible(viz.ON)
	
	#mark the bullet as active
	bullet.active = 1

def MoveBullet(bullet,elapsed):
	global avatarsHit
	#get the bullet's current position
	pos = bullet.get(viz.POSITION)
	
	#calculate the balls future position based on it's velocity
	futurePos = pos + (bullet.vector * elapsed)
	
	#Check if bullet intersected with anything
	info = viz.intersect(pos,futurePos)
	if info.intersected:
		avatarsHit = avatarsHit + 1
		print 'Avatars hit: ', avatarsHit
		print 'intersect point is',info.intersectPoint
		if info.object in avatars:
			WaitThenFreeze = vizact.sequence( vizact.waittime(info.object.getduration(7)-0.005), vizact.speed_node(0) )
			info.object.execute(7)
			info.object.clear(viz.ALL)
			info.object.clear(viz.CURRENT_ACTION)
			info.object.add(WaitThenFreeze) #Add the action to the avatar
			RemoveAvatarAction = vizact.call(RemoveAvatar,info.object)
			info.object.add(RemoveAvatarAction) #Add action to remove avatar

		bullet.visible(0)
		bullet.active = 0
	
	#Update balls positions
	bullet.translate(futurePos.get())

[farshizzo]

Yes, this is how most people implement crosshairs for stereo viewing. Here is a sample script that will place a crosshair 0.1 meters in front of the user.

import viz
viz.go(viz.STEREO)

viz.add('tut_ground.wrl')
viz.clearcolor(viz.GRAY)

crosshair = viz.add(viz.TEXQUAD)
crosshair.texture(viz.add('crosshair.png'))
crosshair.scale(0.01,0.01,0.01)

viz.mouse(viz.OFF)

def ontimer(num):
	line = viz.screentoworld(viz.mousepos())
	v = viz.Vector(viz.get(viz.HEAD_POS))
	dir = viz.Vector(line[3:]) - viz.Vector(line[:3])
	dir.normalize()
	dir *= 0.1 #Place crosshair 1/10th meter in front of user
	v += dir
	crosshair.translate(v.get())
	crosshair.rotatequat(viz.get(viz.VIEW_QUAT))
	
viz.callback(viz.TIMER_EVENT,ontimer)
viz.starttimer(0,0,viz.FOREVER)

[betancourtb82]

Ok, I implemented the crosshair as you said, however I'm still getting an offset between the bullet and the crosshair. Is there anyway to correct this now that I am using the "3d" version of the crosshair? I've attached a copy of the code.

[farshizzo]

I tried your script but I didn't see any bullet. I've modified my previous code so that it shoots a bullet from the center of the viewpoint towards the direction of the crosshair. There will always be an apparent offset between the crosshair and the bullet due to binocular vision.

import viz
viz.go(viz.STEREO)

viz.add('tut_ground.wrl')
viz.clearcolor(viz.GRAY)

crosshair = viz.add(viz.TEXQUAD)
crosshair.texture(viz.add('crosshair.png'))
crosshair.scale(0.01,0.01,0.01)

viz.mouse(viz.OFF)

def ontimer(num):
	line = viz.screentoworld(viz.mousepos())
	v = viz.Vector(viz.get(viz.HEAD_POS))
	dir = viz.Vector(line[3:]) - viz.Vector(line[:3])
	dir.normalize()
	dir *= 0.1 #Place crosshair 1/10th meter in front of user
	v += dir
	crosshair.translate(v.get())
	crosshair.rotatequat(viz.get(viz.VIEW_QUAT))
	
viz.callback(viz.TIMER_EVENT,ontimer)
viz.starttimer(0,0,viz.FOREVER)

bullet = viz.add('white_ball.wrl')

def shoot():
	pos = viz.Vector(viz.get(viz.HEAD_POS))
	dir = viz.Vector(crosshair.get(viz.POSITION)) - pos
	dir.normalize()
	dir *= 10
	bullet.translate(pos.get())
	bullet.goto((pos+dir).get(),3)
vizact.onmousedown(viz.MOUSEBUTTON_LEFT,shoot)

[betancourtb82]

I apologize. I think I sent you something I was working on earlier but I corrected it. I still get the same behavior. Would you mind taking a look at this one and let me know if there is something wrong? Thanks

[farshizzo]

In both calls to viz.screentoworld you are adding an offset to the x position. You don't need to do this when using a 3D cursor. Also, after adding the cursor you should disable collisions on it so the bullet does not hit it.

crosshair.disable(viz.COLLISION)