Vector TO sun or Sun screen position?

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nz0

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Joined: 13th Jun 2007

Location: Cheshire,UK

Posted: 16th Sep 2017 12:37

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So the sun shines on a vector.
I would like to be able to work out the direction vector from the camera to the sun, but I appear to be missing some information to be able to calculate it, such as the sun position.

The sun position in screen co-ords would be most useful.

Nieb posted a useful function for setting the Sun with pitch / yaw

+ Code Snippet

FUNCTION SetSunAngle(Pitch,Yaw)
   xzLen# = cos(Pitch)
   X# = xzLen# * sin(-Yaw)
   Y# = sin(Pitch)
   Z# = -xzLen# * cos(Yaw)
   Print("   SunVec: " + str(X#)+" "+str(Y#)+" "+str(Z#))
   SetSunDirection(X#,Y#,Z#)
ENDFUNCTION

Could this be used in conjunction with camera position/angle to work out the angle to sun or screen co-ords?

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janbo

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Location: Germany

Posted: 16th Sep 2017 21:42 Edited at: 16th Sep 2017 21:49

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You want GetScreenXFrom3D( x, y, z ) while x,y,z is the camera position + direction of the sun

+ Code Snippet

SunScreenX#=GetScreenXFrom3D(CameraX#+DirX#,CameraY#+DirY#,CameraZ#+DirZ#)

I prefer to work with vectors because it is easier to work with/faster to calculate because angles need sin/cos which are "heavy" calculations

if you set the sun direction by yourself then it IS the sun direction as the sun moves with your camera position
if you just want the default sun direction from AppGameKit then it's

+ Code Snippet

-0.3714, -0.7428, 0.5571

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nz0

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Posted: 17th Sep 2017 16:12

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Well, I wanted a direction vector from the camera to the sun, but I eventually worked it out using the pitch / yaw stuff in Nieb's example.

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MadBit

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Posted: 18th Sep 2017 11:58 Edited at: 18th Sep 2017 11:59

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In general, the sunlight is given as a directional vector. So there is no position in the space.
So if you want to make a position from such a vector. Multiply the negative sunlight vector with a fictitious distance. (i dont know is the vector 'from sun' or 'to sun' e.g. not negate the vector)
Then subtract the camera Position from the resulting vector and normalize the result.
Now you have your directionalvector camera-> sun.

sun_pos = (-sun_vec) * distance
cam_to_sun_vec = normalize(sun_pos-cam_pos)

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AppGameKit Classic Chat / Vector TO sun or Sun screen position?