# bump mapping

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righty, i've just got shaders working recently in my engine, so now im trying my hand at doing a bump mapping shader. the problem i have is this: http://users.tpg.com.au/thetwins/fab/bump.JPG L - shows the light position in my scene. A is the vertex lets say (-1, -1), B is (1,1) i'v left out the z-axis, to make things simpler. so left positive x-axis is left, my positive y-axis is down. now, here is my shader code:
struct VS_INPUT
{
float3 position 	: POSITION;
float3 normal 		: NORMAL;
float3 tangent 		: TEXCOORD0;
float3 binormal 	: TEXCOORD1;
float2 uvBump		: TEXCOORD2;
};

struct VS_OUTPUT
{
float4 position : POSITION;
float2 uvBump	: TEXCOORD0;
float3 lightVec : TEXCOORD1;
float3 eyeVec 	: TEXCOORD2;
float3 normal 	: TEXCOORD3;
};

struct PS_OUTPUT
{
float4 colour	: COLOR;
};

//-----------------------------------------------------------------------------
//-----------------------------------------------------------------------------

VS_OUTPUT myvs( const VS_INPUT IN,
uniform float4x4 modelViewProjection,
uniform float4x4 worldView,
uniform float4x4 worldInv,
uniform float3   lightPos,
uniform float3   eyePos )
{
VS_OUTPUT OUT;
OUT.position = mul( modelViewProjection, float4(IN.position, 1.0) );
OUT.uvBump = IN.uvBump;
OUT.normal = IN.normal;

// convert from object space to texture(tangent) space...
float3x3 texSpaceTrans = float3x3(IN.tangent,
IN.binormal,
IN.normal);

float3 lightModelPos = mul( worldInv, float4(lightPos, 1.0) ).xyz;
lightModelPos = lightModelPos - IN.position;
OUT.lightVec = mul( texSpaceTrans, lightModelPos );

float3 eyeModelPos = mul( worldInv, float4(eyePos, 1.0) ).xyz;
eyeModelPos = eyeModelPos - IN.position;
OUT.eyeVec = mul( texSpaceTrans, eyeModelPos );

return OUT;
}

//-----------------------------------------------------------------------------
//-----------------------------------------------------------------------------

PS_OUTPUT myps( VS_OUTPUT IN )
{
PS_OUTPUT OUT;

// normals in bump map are in texture(tangent) space....
float3 bumpTexNormal = tex2D( BumpSampler, IN.uvBump );

// at this stage, should be in tangent(texture) space
float3 eyeVec = normalize( IN.eyeVec );
float3 lightVec = normalize( IN.lightVec );

//OUT.colour = float4(bumpTexNormal, 1.0);
//OUT.colour = float4(lightVec, 1.0);

OUT.colour = max( dot(bumpTexNormal, lightVec), 0.0);

return OUT;
}


note: eye position and ligh position are passed in in world space. it appears that my tangent space light position is all correct, as in the Diagram at the point L is a line comming out, which shows the light position in world space, im not quite sure what the problem is, it seem related to the diagonal line through along the vector (1, -1) :-/ any ideas what i may be doing wrong?

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right seems my problem is that a normal comming strait out has an RGB colour of (128, 128, 128) so i somehow have to offset this to become (0,0,1) :-/

edit: hrmm actually, i tried fixing the normal value to be 0,0,1 and it was all black. so im confused now .... but when i change the normal to (0.5, 0.5, 0.5) i get roughly the same effect/problem i have with my normal map texture

edit2: okay i had to move my light out a bit from the surface *ops*
also i found this which seems to do the trick:

bumpTexNormal = 2 * (bumpTexNormal - 0.5);

but im not sure why?

[Edited by - supagu on May 15, 2005 4:33:26 AM]

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It's simple: Normal maps are color textures that encode normals in their RGB channels. Each channel ranges from [0,1]. But of course each normal coordinate ranges from [-1,1]. When creating a normalmap, you "compress" the normal coordinates by using Nmap=(Norm*0.5+0.5). When reading values of the normalmap, you use Norm=(NMap*2.0-1.0) to expand them into [-1,1].

So, assuming your normalmaps are encoded correctly, it should be:
float3 bumpTexNormal = tex2D( BumpSampler, IN.uvBump )*2.0-1.0;

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