3D Graphics Using OpenGL ES 2.0 - Beginning Android 3D Game Development - page 124

4. Finding the diffuse light amount by taking the dot product between the Vertex

Normal in eye coordinates and the Light Vector in eye coordinates or 0,
whichever is greater

vDiffuse = max(dot(EcLightDir, EcNormal), 0.0);
Listing 4-43 is the full shader code.

Listing 4-43. Diffuse Calculations in the Vertex Shader

// Calculate Diffuse Lighting for vertex
// maximum of ( N dot L, 0)
vec3 WcVertexPos = vec3(uModelMatrix * vec4(aPosition,1));
vec3 WcLightDir = uWorldLightPos - WcVertexPos;
vec3 EcLightDir = normalize(vec3(uViewMatrix * vec4(WcLightDir,1)));
vDiffuse = max(dot(EcLightDir, EcNormal), 0.0);

The vDiffuse shader variable is then passed into the fragment shader as a varying float variable:

varying float vDiffuse;

Specular
The specular value of light is meant to simulate the shine an object gives off when viewed from a
certain angle when being illuminated by a light source—for example, the shine on a chrome bumper
on a car when being hit by the sun's rays and viewed at a certain angle.

The specular light amount for a vertex is calculated by

1. Calculating the vector S, which is the sum of the Light Vector and the Eye

Vector (see Figure 4-24 ).

EyeVec

S = LightVector + EyeVector

PointLight

Eye

Normal

EyeVec

LightVec

Figure 4-24. Specular lighting