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:
https://github.com/openglsuperbible/sb6code/blob/master/bin/media/shaders/equirectangular/render.fs.glsl

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

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

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
it is instead: http://i.imgur.com/F1cxU3g.png

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

it is instead: http://i.imgur.com/01tbFMN.jpg