Efficient Graphics and Portability with OpenGL ES - Pro Android Games - page 123

void main(void)
{
lowp vec3 Color = vec3(1.0, 0.0, 0.0);
mediump vec3 Norm = normalize(NormVec);
mediump vec3 Light = normalize(LighVec);
mediump float Diffuse = dot(Norm, Light);
gl_FragColor = vec4(Color * (max(Diffuse, 0.0) * 0.6 + 0.4), 1.0);
}

Scene Initialization
The scene initialization in Listing 4-11 performs the following steps:

1. It creates two shader programs, vertex, and fragment.

Shader[0] = glCreateShader(GL_VERTEX_SHADER);
Shader[1] = glCreateShader(GL_FRAGMENT_SHADER);

2. It loads the vertex shader.

LoadShader((char *)VertexShader, Shader[0]);

3. It loads the fragment shader. Note that VertexShader and

FragmentShaderRed are two strings describing the shaders in
Listing 3-28 from Chapter 3.

LoadShader((char *)FragmentShaderRed, Shader[1]);

4. It creates the program and attaches the shaders and attributes.

Program = glCreateProgram();
glAttachShader(Program, Shader[0]);
glAttachShader(Program, Shader[1]);

5. It attaches the attributes or variables ( Position and Normal ) used by

the master and shader programs to manipulate the vertex and face
information of the icosahedron.

glBindAttribLocation(Program, 0, "Position");
glBindAttribLocation(Program, 1, "Normal");

6. It links the program using its program ID, glLinkProgram(Program) .

7. It validates the program status by querying the status using the

GL_VALIDATE_STATUS constant.

glValidateProgram(Program);
glGetProgramiv(Program, GL_VALIDATE_STATUS, &ShaderStatus);
if (ShaderStatus != GL_TRUE) {
// handle error
}