[osg-users] textures and shader

[Andreas Goebel]

> "Normal" textures display correctly, but the shadow simply does not appear.
>
> Regards,
>
> Andreas
>   
Hi,

I have solved this. The textur-coordinates for the shadow-texture are 
generated with texGen, so the vertex-shader has to simulate that.

I use the following vertex-shader (which is based on a shader generated 
by ShaderGen):


--------------------------------------shader begin
/*******************************************************
*  Fixed.vert Fixed Function Equivalent Vertex Shader  *
*   Automatically Generated by 3Dlabs GLSL ShaderGen   *
*             http://developer.3dlabs.com              *
*******************************************************/
varying vec4 Ambient;
vec4 Diffuse;
vec4 Specular;
varying vec4 Ambient2;


void pointLight(in int i, in vec3 normal, in vec3 eye, in vec3 ecPosition3)
{
   float nDotVP;       // normal . light direction
   float nDotHV;       // normal . light half vector
   float pf;           // power factor
   float attenuation;  // computed attenuation factor
   float d;            // distance from surface to light source
   vec3  VP;           // direction from surface to light position
   vec3  halfVector;   // direction of maximum highlights

   // Compute vector from surface to light position
   VP = vec3 (gl_LightSource[i].position) - ecPosition3;

   // Compute distance between surface and light position
   d = length(VP);

   // Normalize the vector from surface to light position
   VP = normalize(VP);

   // Compute attenuation
   attenuation = 1.0 / (gl_LightSource[i].constantAttenuation +
       gl_LightSource[i].linearAttenuation * d +
       gl_LightSource[i].quadraticAttenuation * d * d);

   halfVector = normalize(VP + eye);

   nDotVP = max(0.0, dot(normal, VP));
   nDotHV = max(0.0, dot(normal, halfVector));

   if (nDotVP == 0.0)
   {
       pf = 0.0;
   }
   else
   {
       pf = pow(nDotHV, gl_FrontMaterial.shininess);

   }
   Ambient  += gl_LightSource[i].ambient * attenuation;
   Diffuse  += gl_LightSource[i].diffuse * nDotVP * attenuation;
   Specular += gl_LightSource[i].specular * pf * attenuation;
}

vec3 fnormal(void)
{
    //Compute the normal
    vec3 normal = gl_NormalMatrix * gl_Normal;
    normal = normalize(normal);
    return normal;
}

void ftexgen(in vec3 normal, in vec4 ecPosition)
{
    vec4 vertex = gl_ModelViewMatrix * gl_Vertex;

    gl_TexCoord[0] = gl_MultiTexCoord0;
    gl_TexCoord[1].s = dot( ecPosition, gl_EyePlaneS[1] );
    gl_TexCoord[1].t = dot( ecPosition, gl_EyePlaneT[1] );
    gl_TexCoord[1].p = dot( ecPosition, gl_EyePlaneR[1] );
    gl_TexCoord[1].q = dot( ecPosition, gl_EyePlaneQ[1] );


}

void flight(in vec3 normal, in vec4 ecPosition, float alphaFade)
{
    vec4 color;
    vec3 ecPosition3;
    vec3 eye;

    ecPosition3 = (vec3 (ecPosition)) / ecPosition.w;
    eye = vec3 (0.0, 0.0, 1.0);

    // Clear the light intensity accumulators
    Ambient  = vec4 (0.0);
    Diffuse  = vec4 (0.0);
    Specular = vec4 (0.0);

    pointLight(0, normal, eye, ecPosition3);

    color = gl_FrontLightModelProduct.sceneColor +
      Ambient  * gl_FrontMaterial.ambient +
      Diffuse  * gl_FrontMaterial.diffuse;
    color += Specular * gl_FrontMaterial.specular;
    color = clamp( color, 0.0, 1.0 );
    gl_FrontColor = color;
    Ambient2 = gl_FrontLightModelProduct.sceneColor +
      Ambient  * gl_FrontMaterial.ambient;
    gl_FrontColor.a *= alphaFade;
}


void main (void)
{
    vec3  transformedNormal;
    float alphaFade = 1.0;

    // Eye-coordinate position of vertex, needed in various calculations
    vec4 ecPosition = gl_ModelViewMatrix * gl_Vertex;

    // Do fixed functionality vertex transform
    gl_Position = ftransform();
    transformedNormal = fnormal();
    if (dot(transformedNormal,vec3(0.0, 0.0, 1.0) )<0.0)
        transformedNormal = -1.0*transformedNormal;
    flight(transformedNormal, ecPosition, alphaFade);
    ftexgen(transformedNormal, ecPosition);
}

------------------------------shader end


The relevant part for you is the ftexgen-function.

In the fragment shader I use the ambient2-color for the shadow, which 
then fits nicely to the rest of the scene. In the shader I simulate 
two-sided lighting by turning the normal towards the user:

    if (dot(transformedNormal,vec3(0.0, 0.0, 1.0) )<0.0)
        transformedNormal = -1.0*transformedNormal;


This doesn´t give perfect results due to perspective. If someone has a 
better idea here, please tell me.

Of course this shader only works if the shadowtexture uses texture-unit 1.

Regards,

Andreas

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