Ripple effect for GLSL

ripple.frag

// simple fragment shader

// 'time' contains seconds since the program was linked.
uniform float time;

uniform sampler2D tex;
uniform sampler2D tex2;

float radius = .5;

void main()
{
	float t = clamp(time / 6., 0., 1.);

	vec2 coords = gl_TexCoord[0].st;
	vec2 dir = coords - vec2(.5);
	
	float dist = distance(coords, vec2(.5));
	vec2 offset = dir * (sin(dist * 80. - time*15.) + .5) / 30.;

	vec2 texCoord = coords + offset;
	vec4 diffuse = texture2D(tex, texCoord);

	vec4 mixin = texture2D(tex2, texCoord);

 	gl_FragColor = mixin * t + diffuse * (1. - t);
}

ripple.vert

uniform float time;

// simple vertex shader

void main()
{
	gl_Position    = gl_ModelViewProjectionMatrix * gl_Vertex;
	gl_FrontColor  = gl_Color;
	gl_TexCoord[0] = gl_MultiTexCoord0;
}

Hi,

I want to implement Ripple Effect using GLSL shader for iOS. In which, I want to generate ripples from the touch coordinates on screen by user.

Could you help me to implement that?