CS 476: Computer Graphics - Phong Shading Class Exercise
Graphics content developed by Chris Tralie. Module autograding ecosystem designed by Chris Tralie and Bill Mongan.
Exercise Goals
The goals of this exercise are:- Explore how to convert Gouraud shading into Phong shading by moving the appropriate code over from the vertex shader to the fragment shader
Scene
{
"name":"localilluminationscene",
"materials":{
"green":{
"ka":[0.0, 0.4, 0.0],
"kd":[0.0, 1.0, 0.0],
"ks":[0.8, 0.0, 0.0],
"shininess":10
},
"grayblueshine":{
"kd":[0.5, 0.5, 0.5],
"ka":[0.1, 0.1, 0.1],
"ks":[0.0, 0.0, 1.0]
},
"yellow":{
"kd":[0.5, 0.5, 0.2],
"ka":[0.3, 0.3, 0.0],
"ks":[1.0, 1.0, 0.0],
"shininess":5
}
},
"lights":[
{
"pos":[0, 2, 0],
"color":[1, 1, 1]
}
],
"cameras":[
{
"pos": [-0.02,4.02,4.65],
"rot": [0.20,0.02,0.00,0.98]
}
],
"children":[
{
"transform":[20, 0, 0, 0,
0, 20, 0, 0,
0, 0, 20, 0,
0, 0, 0, 1],
"shapes":[
{
"type":"mesh",
"filename":"../assets/js/ggslac/meshes/square.off",
"material":"green"
}
]
},
{
"transform":[2, 0, 0, -2.5,
0, 2, 0, 1,
0, 0, 2, 0,
0, 0, 0, 1],
"shapes":[
{
"type":"mesh",
"filename":"../assets/js/ggslac/meshes/homer.off",
"material":"yellow"
}
]
},
{
"transform":[1, 0, 0, 3,
0, 0, 1, 2,
0, -1, 0, -1,
0, 0, 0, 1],
"shapes":[
{
"type":"mesh",
"filename":"../assets/js/ggslac/meshes/dinopet.off",
"material":"grayblueshine"
}
]
},
{
"transform":[2, 0, 0, 0,
0, 1, 0, 0,
0, 0, 1, 0,
0, 0, 0, 1],
"shapes":[
{
"type":"sphere",
"radius":0.5,
"center":[0, 0, -10],
"material":"green"
}
]
}
]
}
Vertex Shader
precision mediump float;
#define MAX_LIGHTS 10
struct Light {
vec3 pos;
vec3 color;
vec3 atten;
};
// Material properties
uniform vec3 uKa; // Ambient color for material
uniform vec3 uKd; // Diffuse color for material
uniform vec3 uKs; // Specular color for material
uniform float uShininess; // Specular exponent for material
// Transformation/projection matrices
uniform mat4 uMVMatrix;
uniform mat4 uPMatrix;
uniform mat4 tMatrix;
uniform mat3 uNMatrix;
// Light properties
uniform int numLights;
uniform Light lights[MAX_LIGHTS];
// Camera properties
uniform vec3 uEye;
// Per-vertex attributes
attribute vec3 vPos;
attribute vec3 vNormal;
attribute vec3 vColor;
// Stuff to send to fragment shader
varying vec3 color;
void main(void) {
// Transformed position of vertex in homogenous coordinates
vec4 tpos = tMatrix*vec4(vPos, 1.0);
// Transformed normal of vertex
vec3 NT = normalize(uNMatrix*vNormal);
// Viewing window position, taking into consideration the camera
gl_Position = uPMatrix*uMVMatrix*tpos;
vec3 LPos = lights[0].pos; // Position of light
vec3 VPos = tpos.xyz; // Position of the vertex in world coordinates
// Diffuse coefficient
vec3 LVec = normalize(LPos-VPos); // Unit vector from vertex to light
float kdCoeff = dot(NT, LVec);
if (kdCoeff < 0.0) {
kdCoeff = 0.0;
}
// Specular coefficient
vec3 dh = -reflect(LVec, NT);
vec3 h = normalize(uEye-VPos);
float ksCoeff = dot(h, dh);
if (ksCoeff < 0.0) {
ksCoeff = 0.0;
}
ksCoeff = pow(ksCoeff, uShininess);
color = uKa + lights[0].color*(kdCoeff*uKd*vColor + ksCoeff*uKs);
}
Fragment Shader
precision mediump float;
// Camera properties
uniform vec3 uEye;
// Lights
struct Light {
vec3 pos;
vec3 color;
vec3 atten;
};
#define MAX_LIGHTS 10
uniform Light lights[MAX_LIGHTS];
// Material properties
uniform vec3 uKa; // Ambient color for material
uniform vec3 uKd; // Diffuse color for material
uniform vec3 uKs; // Specular color for material
uniform float uShininess; // Specular exponent for material
// TODO: Define other varying properties
varying vec3 color;
void main(void) {
gl_FragColor = vec4(color, 1.0);
}
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