Using vertex shader in our project

In the testApp.h file, in the testApp class declaration, add the shader object declaration as follows:

ofShader shader;  //Shader

At the end of the setup() function declaration, add the following line for loading shaders:

shader.load( "shaderVert.c", "shaderFrag.c" );

Change the empty update() function with the following code:

float time0 = 0;
float phase = 0;
float distortAmount = 0;

void testApp::update(){
  //Compute dt
  float time = ofGetElapsedTimef();
  float dt = ofClamp( time - time0, 0, 0.1 );
  time0 = time;

  float speed = ofMap( mouseY, 0, ofGetHeight(), 0, 5 );
  phase += speed * dt;
  distortAmount = ofMap( mouseX, 0, ofGetWidth(), 0, 1.0 );
}

This function computes time step dt as a time difference between the current time and time of previous calling of the update() function (see details in the Implementing a particle in the project section in Chapter 3, Building a Simple Particle System). Next it computes the phase and distortAmount parameters...