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  #1  
Old 01-28-2011, 06:59 AM
jincheker jincheker is offline
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Join Date: Oct 2009
Posts: 15
Why I need two points for viz.startlayer(viz.POINTS)

Hi, I want to show the points as mouse moves, and I program like below:

Code:
def plotGraph(x,y):
	viz.startlayer(viz.POINTS)
	viz.pointsize(5)
#	viz.vertexcolor(viz.RED)
#	viz.vertex(0,0,0)
	viz.vertexcolor(viz.BLACK)
	viz.vertex(x,y,0)
	line = viz.endlayer(viz.SCREEN)
	print 'plot',x,y

def onMouseMove(e):
	plotGraph(e.x,e.y)

viz.go()
viz.clearcolor(viz.SKYBLUE)
viz.callback(viz.MOUSE_MOVE_EVENT,onMouseMove)
The problem is if i comment
Code:
viz.vertexcolor(viz.RED)
viz.vertex(0,0,0)
The code won't work, but if I uncomment them, then it works.
Can anyone tell me why? Is it because startlayer needs at lease two points?

Thank you
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  #2  
Old 01-28-2011, 08:46 AM
farshizzo farshizzo is offline
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Join Date: Mar 2003
Posts: 2,849
OpenSceneGraph will cull objects that appear very small on screen. Since you have one point, it is computed as infinitely small on screen and not rendered. You can disable viz.CULLING on the node to prevent this from happening:
Code:
line.disable(viz.CULLING)
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