I thought it would be cool to share OSL shaders that folks have been writing for Vray. So in the spirit of the thread of the same name for a certain other software that uses OSL, I thought I’d start one here for Vray. I’ll kick it off by sharing an OSL fabric shader I wrote:
fabric.osl
This is an artist friendly fabric shader. It’s basically an anisotropic Blinn with added sheen and tint terms to capture how the tiny fibers of fabric pick up light at incident angles, and how the specular color of fabrics are often tinted by the diffuse color. The sheen color can also be used to darken the sheen as some fabrics (for example black nylon) are darker at the edges, rather than brighter.
I’d love to hear feedback on the shader, and things that could be done to make it better.
Note that with the current implementation of OSL in Vray the diffuse color slider defaults to black. So you need to change it to be able to see the diffuse contribution. Also since OSL widgets are not implemented yet, the dropdown menu for ramp_type does not work and you need to manually choose one of the 6 options. These options are explained in the comments within the shader code below.
/*
*
* fabric.osl shader by Derek Flood (c)2015
* from http://sharktacos.com/Forums/misc.php?action=help&hid=66
*
*/
float fresnelReflectionFactor(normal bumped_normal, float ior)
{
float c = abs(dot(I, bumped_normal));
float g = ior * ior - 1.0 + c * c;
if (g > 0.0) {
g = sqrt (g);
float A = (g - c) / (g + c);
float B = (c * (g + c) - 1.0) / (c * (g - c) + 1.0);
return 0.5 * A * A * (1.0 + B * B);
}
return 1.0;
}
normal getBumpedNormal(color centerColor, color uColor, color vColor, float inverseBumpAmount)
{
vector worldTangent = normalize(dPdu);
vector worldBitangent = normalize(dPdv);
vector worldNormal = normalize(N);
vector average = vector(0.3333333);
float center = dot (average, vector(centerColor));
float ddu = center - dot(average, vector(uColor));
float ddv = center - dot(average, vector(vColor));
return normalize(ddu * worldTangent + ddv * worldBitangent + inverseBumpAmount * worldNormal);
}
surface fabric
[[ string description = "artist based fabric material" ]]
(
/* Diffuse section */
color Sheen_color = color(1.0, 1.0, 1.0), //This color can be black for nylon sheen.
float Sheen_opacity = 1.0, // Determines amount of sheen effect as fibres pick up light at incident angle.
float Sheen_tint = 0.5, // Tints both the sheen and specular.
string Diffuse_color = "",
float Diffuse_weight = 0.8,
float Roughness = 0.4,
int ramp_type = 3 // Six types of interpolation for sheen. 1-3 are sharper, 4-6 are softer.
[[ string widget = "mapper",
string options = "linear:1|exponential:2|Smooth:3|Sigmoid:4|Square_root:5|Fresnel:6" ]],
/* Spec section */
color Spec_color = 1.0,
float Spec_amount = 0.5,
float Glossiness = 0.6,
float IOR = 1.33, // Fabric generally has low frontal reflections.
int Subdivs = 8,
int Trace_reflections = 1
[[ string widget = "checkBox" ]],
int Fresnel = 1
[[ string widget = "checkBox" ]],
/* Anisotropy section */
float Anisotropy = 0.25, // Fabric is anisotropic due to weave.
float Aniso_rotation = 0,
/* Bump section */
string Bump_texture = "bump.png",
float Bump_amount = 1.0,
output color result = 1 )
{
/* Define Bump */
normal bumped_normal = N;
if (Bump_amount > 0.0)
{
float delta = 0.004;
color center = texture(Bump_texture, u, v);
color uColor = texture(Bump_texture, u + delta, v);
color vColor = texture(Bump_texture, u, v + delta);
bumped_normal = getBumpedNormal(center, uColor, vColor, 1.0 / Bump_amount);
}
/* Define Main color */
color MainColor = texture (Diffuse_color, u, v, "missingcolor", color(1,0,0));
MainColor = pow (MainColor, 2.2);
/* Define Edge color */
color TintBoost = transformc("hsl", MainColor);
TintBoost[2] = pow (TintBoost[2], 0.2);
TintBoost[2] = clamp(TintBoost[2],0,1);
TintBoost = transformc("hsl","rgb", TintBoost);
color EdgeColor = Sheen_color / 10;
color TintEdge = EdgeColor * TintBoost;
EdgeColor = mix (EdgeColor, TintEdge, Sheen_tint);
EdgeColor = clamp (EdgeColor, 0, 1);
/* Define Spec color */
color SpecColor = Spec_color;
color TintedSpec = SpecColor * TintBoost;
SpecColor = mix (SpecColor, TintedSpec, Sheen_tint);
/* Define Ramp */
float facingRatio = 1 - abs(dot(I, bumped_normal));
if( ramp_type == 1) // linear
{facingRatio = facingRatio; }
if( ramp_type == 2) // exponential (Down)
{ facingRatio *= facingRatio; }
if( ramp_type == 3) // smooth
{ facingRatio = smoothstep (0,1, facingRatio ); }
if( ramp_type == 4) // sigmoid S-curve
{
float Sigmoid = facingRatio / (1 + abs(facingRatio));
facingRatio = clamp( 2 * Sigmoid, 0, 1);
}
if( ramp_type == 5) // square root
{ facingRatio = sqrt (facingRatio); }
if( ramp_type == 6) // fresnel
{ facingRatio = 2 * fresnelReflectionFactor(bumped_normal, IOR); }
/* Fresnel */
if (Fresnel)
{ SpecColor *= fresnelReflectionFactor(bumped_normal, IOR); }
if (Trace_reflections)
{ MainColor *= (1.0 - SpecColor); }
/* BRDF Mixes*/
color SheenMix = EdgeColor * facingRatio * Sheen_opacity;
color EdgeMask = mix(1, Sheen_color, (facingRatio * Sheen_opacity) );
MainColor *= EdgeMask;
MainColor *= (1.0 - SheenMix);
closure color sheen_component = SheenMix * diffuse(bumped_normal, "roughness", Roughness);
closure color diffuse_component = MainColor * Diffuse_weight * diffuse(bumped_normal, "roughness", Roughness);
closure color specular_component = Spec_amount * SpecColor *
vray_blinn (bumped_normal, Glossiness, Anisotropy, Aniso_rotation,
"subdivs", Subdivs, "trace_reflections", Trace_reflections);
closure color reflect_component = SpecColor * reflection(bumped_normal, IOR);
Ci = diffuse_component + specular_component + reflect_component + sheen_component;
}
