DuartePeixinho.com http://www.duartepeixinho.com DuartePeixinho.com Merry Christmas to you all http://www.duartepeixinho.com/post/7/ And a Happy New Year!!!

MerryChristmas

(and here it is, a model loaded into my engine, it had to be a geeky Christmas wish, right? ;) )
 Environment Reflection Help http://www.duartepeixinho.com/post/6/ While I was developing some materials for my little C++/OpenGL engine, I tried to create an environment reflection map (also known as cubemap reflection). It's one of my favorite effects and since I couldn't find any solution online, I'm going to share my own solution.

I'm just going to focus to the vertex and fragment shaders, I suppose that you know how to send uniforms and attributes to the shaders.

The secret about this shader is to calculate the camera direction to the vertex position, and that calculation have to be done on World Space. In the Vertex Shader you have to send the Camera Position in World Coordinates, and the Model Matrix (sometimes called Model To World Matrix) to be able to calculate the vertex position in World Coordinates.
All the other uniforms are common to almost all shaders.



// Vertex Shader



attribute vec3 aPosition, aNormal;

uniform vec3 CameraPos;

uniform mat4 ModelViewProjectionMatrix, NormalMatrix, ModelMatrix;

varying vec3 vReflection;

void main() {

      // normal and position calculation

      vec3 normal = normalize(NormalMatrix * vec4(aNormal,1)).xyz;

      gl_Position = ModelViewProjectionMatrix * vec4(aPosition,1);



      // Here is the environment map calculation

      //

      // First you have to calculate the Vertex Position in WorldPosition

      // So you just need to multiply the Position by the ModelMatrix

      vec3 vertex = (ModelMatrix * vec4(aPosition,1)).xyz;

      // Now you have to do the same to the Normal, so you multiply

      // the normal by the ModelMatrix (don't use the Normal calculated 

      // before)

      vec3 N = normalize((ModelMatrix * vec4(aNormal,0)).xyz);

      // The Incident value is the different of vertex and camera position

      // (both on world coordinates)

      vec3 I = vertex - CameraPos;

      // Finaly you just simply calculate the reflection using reflect

      // and as it is a varying variable, it is sent to the Fragment Shader

      vReflection = reflect(I,N);

}
For the Fragment Shader you just need to send the samplerCube (it is just a combination of 6 images, one for each side of the cube).


// Fragment Shader



uniform samplerCube CubeMap;

varying vec3 vReflection;

void main() {

      // Get the pixel color from the samplerCube using the Reflection that

      // was calculated on the Vertex Shader

      vec4 cubeColor = textureCube( CubeMap, vReflection );

      // Just send the Color to the gl_FragColor

      gl_FragColor = cubeColor;

}


Here is an example:
CubeMap

Now, you can add other stuff, like reflection factor, lighting and much more. Some old flash experiments http://www.duartepeixinho.com/post/5/ I think it should be nice to post some of my old flash experiments that I left on Wonderfl.net.

As3 Tree: