Dynamic Sphere Texturing

amokk_gw

I'm creating dynamic textures for planets. This is working pretty good, however there is one problem.
As everybody who already textured a sphere knows: With a normal rectangular texture the sphere shows a large distortion at the poles.

In a manual process, the texture could be fixed in photoshop, but this is not possible for calculated textures. I've tried to write the algorithm that Photoshop uses in their Polar Coordinates filter. There are various of sources for this in the net moving pixel by pixel. The issue here was that the algorithm was way to slow and took several seconds for a 4K texture.
Photoshop can apply the filter almost immediately.

I've also experimented with other geometry like a Geosphere or a Quadsphere. The Geosphere has similar issues with the poles as the normal sphere and the Quadsphere shows nasty seams.

Has anyone experience with procedural sphere texturing and can point me to the right direction?

Noors

Could 3 planar mapping shader help you ?
http://gamedevelopment.tutsplus.com/articles/use-tri-planar-texture-mapping-for-better-terrain--gamedev-13821

amokk_gw

Hey Noors

That could work, I'll have to test it, but I don't think that the performance would be a problem in my case. I'll report back here once I tested it.

Noors

I know little about shader programming but iI imagine you could also use regulars uv and only use projections at the poles to a certain angle.

Obscura

Noors - Thanks for pointing out this technique! Looks very useful.

Obscura

Here is the implementation in Unity and UDK if anyone interested:
http://www.martinpalko.com/Tutorials/TriplanarMapping/TriplanarMapping.html

amokk_gw

Okay I've managed to get a pretty good result with the new shader.
I've used the shader from here and modified it a little bit to fit my needs:
http://www.blog.radiator.debacle.us/2013/02/a-smoother-triplanar-shader-for-unity.html

And if somebody has a use for it, here is my complete shader in Unity:

Shader "Triplanar/Tri-Planar Sphere" {
Properties {
_MainTex ("Base (RGB)", 2D) = "white" {}
_BumpMap ("Normalmap", 2D) = "bump" {}
_PoleScale ("Pole Scale", Float) = 2
_PoleFlow ("Pole Flow", Float) = 15
_PoleStart ("Pole Start", Float) = 1.01
}
SubShader {
Tags {
"Queue"="Geometry"
"IgnoreProjector"="False"
"RenderType"="Opaque"
}

Cull Back
ZWrite On
CGPROGRAM
#pragma surface surf Lambert vertex:vert
#pragma exclude_renderers flash
#pragma target 3.0
#pragma exclude_renderers d3d11 d3d11_9x

sampler2D _MainTex, _BumpMap;
float _PoleScale, _PoleFlow, _PoleStart;
struct Input {
float3 worldPos;
float3 worldNormal;
float3 wNormal;
float2 uv_MainTex;
float2 uv_BumpMap;
};
void vert(inout appdata_full v, out Input o) {
o.worldPos = mul(_Object2World, v.vertex).xyz;
o.worldNormal = mul(_Object2World, float4(v.normal, 0.0)).xyz;
o.wNormal=o.worldNormal;
}

void surf (Input IN, inout SurfaceOutput o) {
float3 projNormal = saturate(pow(IN.wNormal * _PoleStart, _PoleFlow));

float3 y = tex2D(_MainTex, frac(IN.worldPos.zx * _PoleScale)) * abs(IN.wNormal.y);
o.Normal = UnpackNormal (tex2D (_BumpMap, IN.uv_BumpMap));
o.Albedo = tex2D(_MainTex, IN.uv_MainTex);
o.Albedo = lerp(o.Albedo, y, projNormal.y);

}
ENDCG
}
Fallback "Diffuse"
}

It's a bit nasty and I don't know the performance but the result is very good for me. Please note that the normal mapping is not working at the poles. I couldn't manage to get that working.