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## faster equirectangular sampling

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### #1Yours3!f  Members

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Posted 29 March 2014 - 04:15 PM

Hi there,

I'm doing image based lighting, and I need to sample a texture that has an equirectangular projection layout.

I've got this function to sample it:

vec4 sample_equirectangular_map(vec3 dir, sampler2D sampler, float lod)
{
vec2 uv;
uv.x = atan( dir.z, dir.x );
uv.y = acos( dir.y );
uv /= vec2( 2 * pi, pi );

return textureLod( sampler, uv, lod );
}


where dir is the normalized world-space normal.

The texture wrapping is set to GL_REPEAT, so negative values don't hurt.

This works well, but I kinda have the feeling that the atan and acos aren't really needed there...
so I found this from oglsuperbible 6, but when I put that in, it didn't really work:

vec4 sample_equirectangular_map(vec3 dir, sampler2D sampler, float lod)
{
vec2 uv;
uv.y = dir.y;
dir.x = normalize( dir.xz ).x * 0.5;
float s = sign( dir.z ) * 0.5;
uv.x = 0.75 - s * (0.5 - uv.x);
uv.y = 0.5 + 0.5 * uv.y;

return textureLod( sampler, uv, lod );
}


Any ideas how to remove the atan/acos from there?

the ibl maps I sampled are from here:
http://www.hdrlabs.com/sibl/archive.html

Best regards,

Yours3!f

### #2Chris_F  Members

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Posted 29 March 2014 - 06:06 PM

dir.x = normalize( dir.xz ).x * 0.5;


You are normalizing a vec2, this is not the same as the OGLSB example.

### #3Yours3!f  Members

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Posted 30 March 2014 - 03:10 AM

dir.x = normalize( dir.xz ).x * 0.5;


You are normalizing a vec2, this is not the same as the OGLSB example.

well x / sqrt( x^2 + z^2 ) should be equal to x / sqrt( x^2 + 0^2 + z^2 )

so it's essentially the same

Edited by Yours3!f, 30 March 2014 - 03:11 AM.

### #4Chris_F  Members

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Posted 30 March 2014 - 03:30 AM

In that case can you elaborate on what you mean by "it didn't really work"?

### #5Yours3!f  Members

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Posted 30 March 2014 - 04:40 AM

In that case can you elaborate on what you mean by "it didn't really work"?

diffuse:

should be: http://i.imgur.com/3Epr2Sf.png

EDIT: it's a bit more evident using the reflection texture
should be: http://i.imgur.com/3uPHQLG.jpg