View Full Version : Print Particle Screen positions to file.

01 January 2009, 01:29 PM
That shouldn't be too hard, just calculate back to a float value (0...1) that way you can multiply it with every size you want.

This below code I use to transport 3d positions to 2d screenspace for use in fusion. 3Dto2D tracker data sort of speech.

pX = stringStream ""
pY = stringStream ""

sX = gw.getWinSizeX() as float -- Get WinSize X
sY = gw.getWinSizeY() as float -- Get WinSize X

rPA = renderPixelAspect -- Get Render Pixel Aspect

rX = RenderWidth as float -- Get Render Pixels X
rY = RenderHeight as float -- Get Render Pixels Y

rY = rY * ( 1 / rPA ) -- Correct for aspect ratio

rratio = ( sX / rX ) / (sY / rY) -- Get Ratio
if rratio >= 1. then ( -- If Ratio is bigger than 1 then
ratio = sY / rY -- Use Y ratio for calculations
) else (
ratio = sX / rX -- Else use X ratio for calculations
) -- end if

xMin = ( sX - ( rX * ratio ) ) / 2 -- Get x minimum value
yMin = ( sY - ( rY * ratio ) ) / 2 -- Get y minimum value

ct = animationRange.end as integer / TicksPerFrame -- Animation range end as integer
gw.setTransform (matrix3 1) -- Set gw View transform to zero

for i = 0 to ct do
--p = gw.TransPoint ( at time i obj.position ) -- Get 3D point in 2D screenspace
slidertime = i -- Move viewport cause of moving cams
p = gw.TransPoint ( obj.position ) -- Get 3D point in 2D screenspace

x = ( p.x - xMin ) / ( sX - ( xMin * 2) ) -- Convert View space to Render space for X
y = 1 - ( p.y - yMin ) / ( sY - ( yMin * 2 ) ) -- idem for Y

format "% %\n" ( i as float ) x to:pX
format "% %\n" ( i as float ) y to:pY
) -- end for

Be aware this assume topleft as [0,0].
At least I hope this gets you on your way if I understood the question right and you want to convert 3D position to 2D screen data.


01 January 2009, 01:43 PM
There are time-travellers among us

01 January 2009, 02:32 PM
I'm working on a still image with a few thousand particles in. I need to keep a log of the positions of the particles on the render.

My particles are all on one plane. and the bottom left corner of the plane is at 0,0

I can print the x.pos and y.pos and multiply this to get a fairly accurate position as am rendering with an isometric camera, but have to deal with bleed.

Is there a way to print the screen position relative to the render size...


01 January 2009, 03:55 PM
Cheers for that.

Something appears to be wrong with cgtalk at the mo...

01 January 2009, 04:35 PM
just to add.. beware of using the floats if you're going to be printing to file... format "%" <float> only gives you so much precision. Compound that with the already-quirky float from the 3D->2D function and odds are that on larger plates you will run into precision issues.

01 January 2009, 05:00 PM
My image will be about 8000x6000 pixels, so yes I guess I might run into precision problems.

I think I might be able to do it without doing any complex 3d-2d vector work as the camera is isometric and all the particles are on one plane. I just need to do some multiplication and add some numbers onto their X and Y co-ords. Doesn't have to be pixel perfect and is only for one frame.

Interesting to see how one could calculate it's 3d-2d position though.

I thought there might have been a way using screen co-ords system to get an X and Y pos.

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01 January 2009, 05:00 PM
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