Shading Technique - Fresnel

Overview What is the Fresnel shader? This shader combine reflection and refraction that depends on the viewing angle. What is refraction? According to the "OpenGL Shading Language Book", refraction is the blending of light as it passes trough a boundary between surfaces with different optical densities. Requirements: - A cube map texture. The shader Can be put in the ATTRIBPASS or AMBIENT context to be used with the examples pipelines in the Horde3D SDK 1.0 beta. Vertex shader: In the vertex shader, you can freely change the indices of refraction or the degree of reflectivity to change de final result. Fresnel - Vertex Shader const float Eta = 0.67; // Ratio of indices of refraction (air -> glass) const float FresnelPower = 10.0; // Controls degree of reflectivity at grazing angles const float F = ((1.0 - Eta) * (1.0 - Eta)) / ((1.0 + Eta) * (1.0 + Eta)); varying vec3 Reflect; varying vec3 Refract; varying float Ratio; attribute vec3 normal; uniform vec3 viewer; void main( void ) { vec4 worldPosition = calcWorldPos( gl_Vertex ); vec3 ecPosition3 = worldPosition.xyz - viewer;//viewer - worldPosition.xyz; vec3 i = normalize(ecPosition3); vec3 n = normalize( calcWorldVec(normal) ); Ratio = F + (1.0 - F) * pow((1.0 - dot(-i, n)), FresnelPower); //Ratio = 1.0 - Ratio; // Add this line if your cube map is not based on the right side Refract = refract(i, n, Eta); Refract = vec3(gl_TextureMatrix[0] * vec4(Refract, 1.0)); Reflect = reflect(i, n); Reflect = vec3(gl_TextureMatrix[0] * vec4(Reflect, 1.0)); gl_Position = gl_ModelViewProjectionMatrix * worldPosition; } Fragment shader: Fresnel - Vertex Shader varying vec3 Reflect; varying vec3 Refract; varying float Ratio; uniform samplerCube tex0; void main(void) { vec3 refractColor = vec3 (textureCube(tex0, Refract)); vec3 reflectColor = vec3 (textureCube(tex0, Reflect)); vec3 color = mix(refractColor, reflectColor, Ratio); gl_FragColor = vec4(color, 1.0); } How to use it You must create a material in wich the shader is defined as the fresnel shader. Then, you must add the Texture unit 0 with a cube map type texture. Example Result http://www.horde3d.org/forums/download/file.php?id=52 Pictures To-Do List for this Article - Better explanation

Technique - Fresnel [[Image:]] Using reflection and refraction Version: 1.0 Compatible with Horde3D: 1.0 beta Release date: 2008-08-10 Author(s): Mikmacer