VertexShader.vert

//-------------------------------------------------------
// Filename: VertexShader.vert
//
// Description: A vertex shader that implements coloring based upon attenuation and diffusion.
//
// Creator:  Professor Corey McBride for MEEN 570 - Brigham Young University
//
// Based On: http://www.learnopengles.com/android-lesson-two-ambient-and-diffuse-lighting/
//
// Creation Date: 10/10/16
//
// Owner: Corey McBride
//-------------------------------------------------------

#version 120
uniform mat4 u_MVPMatrix;     // A constant representing the combined model/view/projection matrix.
uniform mat4 u_MVMatrix;      // A constant representing the combined model/view matrix.
uniform vec3 u_LightPos;      // The position of the light in eye space.
//uniform vec3 u_Color;

attribute vec3 a_Color;
attribute vec3 a_Position;    // Per-vertex position information we will pass in.
attribute vec3 a_Normal;      // Per-vertex normal information we will pass in.

varying vec3 v_Color;         // This will be passed into the fragment shader.

// The entry point for our vertex shader.
void main()
{
    // Transform the vertex into eye space.
    vec3 modelViewVertex = vec3(u_MVMatrix * vec4(a_Position,1.0));

    // Transform the normal's orientation into eye space.
    vec3 modelViewNormal = vec3(u_MVMatrix * vec4(a_Normal, 0.0));

    // Will be used for attenuation.
    float distance = length(u_LightPos - modelViewVertex);

    // Get a lighting direction vector from the light to the vertex.
    vec3 lightVector = normalize(u_LightPos - modelViewVertex);

    // Calculate the dot product of the light vector and vertex normal. If the normal and light vector are
    // pointing in the same direction then it will get max illumination.
    float diffuse = max(dot(modelViewNormal, lightVector), .1);

    // Attenuate the light based on distance.
    diffuse = diffuse * (1.0 / (1.0 + (0.01 * distance * distance)));
    diffuse = clamp(dot(modelViewNormal,lightVector),0.0,1.0);

    // Multiply the color by the illumination level. It will be interpolated across the triangle.
    v_Color = a_Color * diffuse;

    // gl_Position is a special variable used to store the final position.
    // Multiply the vertex by the matrix to get the final point in normalized screen coordinates.
    gl_Position = u_MVPMatrix * vec4(a_Position,1.0);
}