Pro OpenGL ES for iOS

320 CHAPTER 10: OpenGL ES 2, Shaders, and...^

glEnable(GL_DEPTH_TEST);

m_EyePosition=GLKVector3Make(0.0,0.0,65.0);

m_WorldModelViewMatrix=GLKMatrix4MakeTranslation(-m_EyePosition.x,-m_EyePosition.y,-

m_EyePosition.z);

m_Sphere=[[Planet alloc] init:planetSize slices:planetSize radius:10.0f squash:1.0f

textureFile:NULL];

[m_Sphere setPositionX:0.0 Y:0.0 Z:0.0];

m_EarthDayTexture=[self loadTexture:@"earth_light.png"];

m_EarthNightTexture=[self loadTexture:@"earth_night.png"];

m_LightPosition=GLKVector3Make(100.0, 10,100.0); //behind the earth

}

In loadShaders() I merely added one more attribute, namely, texCoord, or the texture

coordinates. These are recovered in the fragment shader:

glBindAttribLocation(*program, ATTRIB_VERTEX, "position");

glBindAttribLocation(*program, ATTRIB_NORMAL, "normal");

glBindAttribLocation(*program, GLKVertexAttribTexCoord0, "texCoord");

I also pass the light’s position as a uniform, instead of hard-coding it in the vertex

shader. This is set up in a couple of steps:

„ First, add it to the shader: uniform vec3 lightPosition;.

„ Then in loadShaders(), you fetch its ‘‘location’’ using

glGetUniformLocation(). That merely returns a unique ID for this

session that is then used when setting or getting data from the shader.

„ The light’s position can then be set by using this:

glUniform3fv(uniforms[UNIFORM_LIGHT_POSITION],1,m_LightPosition.v);

Then change the call to add two parameters so that it can be called with different shader

names, and add a pointer to a progam handle. And remember to change the code to

support the parameters instead of the temp variables:

• (BOOL)loadShaders:(GLuint )program shaderName:(NSString )shaderName
  Now in Listing 10-9, both sides of the earth are drawn, with the night side going first,
  while the daylight side goes second. The programs are swapped as needed.
  Listing 10-9. The drawInRect() Method to Handle This Situation


• (void)glkView:(GLKView *)view drawInRect:(CGRect)rect
  {
  GLfloat gray=0.0;
  static int frame=0;