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whathappened

Parallax mapping

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I dont really know if this topic fits into the DirectX forum but I hope so since it's about shaders. I just wonder, what is parallax mapping? I know how to make bump mapping and some displacement mapping (to actual change the geometry) but what is parallax mapping? Anyone who has a good link where it's explained cause I couldnt find one

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Also, in case you are interested in an actual implementation, a Parallax Mapping sample has been recently added to the SDK samples. Grab the April '06 SDK to give it a go.

Hope this helps. :)

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Don't know about a tutorial, but if you google "parallax mapping site:ati.com" you should find a couple of docs. ATI's March SDK contains an article about this.

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Its quite simple, actually. It only requires a heightmap texture for the shader pass.


float3 vEye = -TBNViewDir;
float fBumpScale = 0.05f;
float2 vCoord = texCoord;

float fDepth = tex2D(sHeightMapSampler, vCoord).w;
float2 vHalfOffset = normalize(vEye).xy * (fDepth) * fBumpScale;

fDepth = (fDepth + tex2D(sHeightMapSampler, vCoord + vHalfOffset).x) * 0.5;
vHalfOffset = normalize(vEye).xy * (fDepth) * fBumpScale;

fDepth = (fDepth + tex2D(sHeightMapSampler, vCoord + vHalfOffset).x) * 0.5;
vHalfOffset = normalize(vEye).xy * (fDepth) * fBumpScale;

return vCoord + vHalfOffset;


Then, sample the diffuse texture and the normal texture using the returned coordinates.

Basically, it samples the height map at the texture coordinate, and offsets the texture coordinates in the direction away from the viewer. I do 3 iterations to get good results. If you only do one, the effect is negligible.

In these 2 screenshots, I have doubled the parallax amount to make the difference clearly visible.


No parallax mapping


Parallax mapping

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Ah cool, I didn't think about multiple samples/calculations. Does that increase accuracy or create a larger offset?

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Cadef, in the second screenshot if seems like your parallax mapping goes off to the left. Maybe a projection problem?

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Multiple samples increase accuracy. If you take 1 sample, it will look wrong.

It is supposed to go off to the left, that is parallax mapping. It might seem a bit wrong, because I exaggerated the parallax scale to make the effect prominent.

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So parallax mapping is just about the texture coordinates? Would be great with a little more detailed explanation :)

and does anyone know any links where I can find a simple texture and a nice parallax map to work with :)

[Edited by - whathappened on April 16, 2006 7:25:58 AM]

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Quote:
and does anyone know any links where I can find a simple texture and a nice parallax map to work with :)


The aforementioned SDK sample...

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Yes, parallax mapping is just about pushing texture coordinates away from the camera. How far it is pushed, depends on EyeVector * ParallaxMappingScale

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