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# Raytraced diffuse lighting...

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ok, im working on a ray tracer... but im not sure how to correctly calculate the lighting... ive googled, but there isnt very much at all on the subject... this is what i Have so far:

// ...

if(pHitObject)
{
CVECTOR3 vecNormal = pHitObject->vecCenter - vecHitLocation;
// It can only do spheres at the moment :)

// this is the part that doesnt work, ive read this way, and a way using the cross product

CVECTOR3 vecLighting = vecHitLocation - vecPointLightPos;
vecLighting.Normalize();
float fAngle = vecLighting.Dot(vecNormal);

dwPixelColor = // what goes here??

}
else
{
dwPixelColor = 0x00000000;
}


MasterDepot [edited by - elis-cool on February 9, 2003 6:08:38 AM]

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float fAngleCosine = vecLighting.Dot(vecNormal);

The dotproduct doesn''t give you the angle, but the cosine of the angle. And that value happens to be directly the lighting factor you need:

RGB PixelColour = (fAngleCosine <= 0) ? RGB(0, 0, 0) : fAngleCosine * ColourOfHitObject * ColourOfLight * DistanceAttenuation ...etc... ;

dwPixelColor = ConvertToDWORD(PixelColour);

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Thanks Yann, I pretty much had that... but im not sure about the color values, like are they meant to be in the range 0.0 - 1.0? how do I convert a dword color to and from that range?

MasterDepot

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Best thing would be to keep all colours in the 0..1 range. Then, at the very last step (when drawing a pixel), convert them to the 0..255 range.

So your RGB PixelColour would have 3 floating point components (add alpha, if you like/need), each one ranging from 0 to 1.

To convert those into a DWORD, you need to know the layout of the colour components. That depends on your particular API. The conversion is just a range remap from 0..1 to 0..255, and then some bitshifting.

If your DWORD component layout was eg. ARGB, then the conversion would look something like this:
PixelColour *= 255.0f;  // multiply all components with 255 (make sure that they are clamped to 0..1 first !DWORD = ((int)PixelColour.a << 24) | ((int)PixelColour.r << 16) | ((int)PixelColour.g << 8) | ((int)PixelColour.b);

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Thanks yann, but is fAngleCosine meant to be going over 1.0? it seems to be in the range 0.0 - ~5.0, so when its multiplying the colors together it overflows the 1.0 boundry, and so the would be bright spot on the sphere ends up with other colors... but if I cap it to 1.0 then and there (instead of at the last convert to dword step) then the bright spot ends up as just one big flat shaded color in the middle then it shades off to black around the edges...

500x1

MasterDepot

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If vecNormal is a normalized vector, it should not be returning 5.. it should return a value between 0 and 1.

-1 0 0 dot -1 0 0 = 1
0 0 0 dot 0 0 0 = 0
0 1 0 dot 0 1 0 = 1
.5 .5 0 dot .5 .5 0 = .5
-.5 0 .5 dot -.5 0 .5 = .5
As you can see, there is no way for a normalized vector dot producted with itself to be outside the 0 -> 1 range.

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ok, so I normalized the normal vecter, I thought this was supposed to normalize it though, it cant have been...
CVECTOR3 vecNormal = pHitObject->vecCenter - vecHitLocation;    // It can only do spheres at the moment     vecNormal.x /= pHitObject->radius;    vecNormal.y /= pHitObject->radius;    vecNormal.z /= pHitObject->radius;

well anyway, its working now...

MasterDepot

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