GLSL Shader and Processing - 2D example

lens.glsl

// shader example for Processing
// uniform - variables set in Processing sketch using shader.set()
// varying - variables set by Processing itself

// image to process
uniform sampler2D texture;
// mouse position normalized
uniform vec2 inp;

// vertex color
varying vec4 vertColor;
// vertex position
varying vec4 vertTexCoord;

#define TWO_PI (6.28318530718)

void main() {	
  vec4 col = texture2D(texture,vertTexCoord.xy); // take color from texture
  float lumaang =  TWO_PI*(0.2126 * col.r + 0.7152 * col.g + 0.0722 * col.b); // calculate luma 
  vec2 off = vec2(2.0*inp.x*sin(lumaang),2.0*inp.y*cos(lumaang)); // calculate offset vector from luma angle
  gl_FragColor = vec4(texture2D(texture, fract(vertTexCoord.st+off)).rgb,1.0); // set color from texture from current position + offest. Wrapped.
}

shader_test.pde

// generateme.tumblr.com
// using OpenGL shader example
// imagelens

// shader declaration
PShader sh;

String uid;

void setup() {
  uid = hex((int)random(0x10000),4);
  PImage img = loadImage("test.jpg");
  
  size(img.width,img.height,P2D);
  background(0);
  
  // load and compile shader
  sh = loadShader("lens.glsl");
  // upload texture to graphics card
  sh.set("texture",img);
}

void draw() {
  // normalize mouse position
  float inpx = mouseX/(float)width;
  float inpy = mouseY/(float)height;
  
  // set shader variable
  sh.set("inp",inpx,inpy);
  
  // run shader
  shader(sh);
  
  // fill whole window
  rect(0,0,width,height);
}

void keyPressed() {
  saveFrame("res"+uid+"######.jpg");
}