Why normalize it?

noatom · 2012-08-09T21:41:58

Ok,I'm rereading the Introduction to 3D Game Programming with Dx10,and I'm at the Lightning chapter. Here's the HLSL code: [source lang="cpp"]//============================================================================= // lighthelper.fx by Frank Luna (C) 2008 All Rights Reserved. // // Structures and functions for lighting calculations. //============================================================================= struct Light { float3 pos; float3 dir; float4 ambient; float4 diffuse; float4 spec; float3 att; float spotPower; float range; }; struct SurfaceInfo { float3 pos; float3 normal; float4 diffuse; float4 spec; }; float3 ParallelLight(SurfaceInfo v, Light L, float3 eyePos) { float3 litColor = float3(0.0f, 0.0f, 0.0f); // The light vector aims opposite the direction the light rays travel. float3 lightVec = -L.dir; // Add the ambient term. litColor += v.diffuse * L.ambient; // Add diffuse and specular term, provided the surface is in // the line of site of the light. float diffuseFactor = dot(lightVec, v.normal); [branch] if( diffuseFactor > 0.0f ) { float specPower = max(v.spec.a, 1.0f); float3 toEye = normalize(eyePos - v.pos); float3 R = reflect(-lightVec, v.normal); float specFactor = pow(max(dot(R, toEye), 0.0f), specPower); // diffuse and specular terms litColor += diffuseFactor * v.diffuse * L.diffuse; litColor += specFactor * v.spec * L.spec; } return litColor; } float3 PointLight(SurfaceInfo v, Light L, float3 eyePos) { float3 litColor = float3(0.0f, 0.0f, 0.0f); // The vector from the surface to the light. float3 lightVec = L.pos - v.pos; // The distance from surface to light. float d = length(lightVec); if( d > L.range ) return float3(0.0f, 0.0f, 0.0f); // Normalize the light vector. lightVec /= d; // Add the ambient light term. litColor += v.diffuse * L.ambient; // Add diffuse and specular term, provided the surface is in // the line of site of the light. float diffuseFactor = dot(lightVec, v.normal); [branch] if( diffuseFactor > 0.0f ) { float specPower = max(v.spec.a, 1.0f); float3 toEye = normalize(eyePos - v.pos); float3 R = reflect(-lightVec, v.normal); float specFactor = pow(max(dot(R, toEye), 0.0f), specPower); // diffuse and specular terms litColor += diffuseFactor * v.diffuse * L.diffuse; litColor += specFactor * v.spec * L.spec; } // attenuate return litColor / dot(L.att, float3(1.0f, d, d*d)); } float3 Spotlight(SurfaceInfo v, Light L, float3 eyePos) { float3 litColor = PointLight(v, L, eyePos); // The vector from the surface to the light. float3 lightVec = normalize(L.pos - v.pos); float s = pow(max(dot(-lightVec, L.dir), 0.0f), L.spotPower); // Scale color by spotlight factor. return litColor*s; } [/source] note SurfaceInfo is the vertex that is not getting his color computed As you can see there are 3 types of light defined above.But to create the spotlight,it creates a pointlight and then it needs to actually make that pointlight a spotlight,the thing is,I don't understand why on this line: float3 lightVec = normalize(L.pos - v.pos) it uses normalize?Why use normalize? Wouldn't it be the same thing without normalize?!

Graphics and GPU Programming Programming

Started by noatom August 08, 2012 09:51 PM

11 comments, last by Mussi 11 years, 8 months ago

noatom

927

Author

August 09, 2012 08:41 PM

So the final advice is to normalize every vector that I use in dot product no matter what?

Madhed

4,095

August 09, 2012 09:07 PM

I'm sorry to say, but you will need to learn at least the basics of linear algebra to understand what's going on there in the pixel shader. On the other hand it's not that complicated.
I'd say if you're confident in programming you will grasp the math pretty easily.

Mussi

4,453

August 09, 2012 09:41 PM

So the final advice is to normalize every vector that I use in dot product no matter what?

No, there are plenty of cases where you don't want to normalize a vector used in a dot product. It depends on what you're trying to do. In this case you're interested in the angle between the vectors, the dot product of two normalized vectors gives you the cosine of that angle. So in this case, you want both vectors to be normalized.

Why normalize it?

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Why normalize it?

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