droste capture

Author: monkstone

processing_app/library/glvideo/data/droste.glsl

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+// This implementation is based on GLSL code by ArKano22:
+// http://www.gamedev.net/topic/590070-glsl-droste/
+uniform float globalTime;
+uniform sampler2D texture; // iChannel0 in Shadertoy
+uniform vec2 sketchSize; // iResolution in Shadertoy
+uniform int mode;
+
+const float TWO_PI = 3.141592*2.0;
+//ADJUSTABLE PARAMETERS:
+const float Branches = 1.0;
+const float scale = 0.4;
+const float off = 0.6;
+//Complex Math:
+vec2 complexExp(in vec2 z){
+	return vec2(exp(z.x)*cos(z.y),exp(z.x)*sin(z.y));
+}
+vec2 complexLog(in vec2 z){
+	return vec2(log(length(z)), atan(z.y, z.x));
+}
+vec2 complexMult(in vec2 a,in vec2 b){
+	return vec2(a.x*b.x - a.y*b.y, a.x*b.y + a.y*b.x);
+}
+float complexMag(in vec2 z){
+	return float(pow(length(z), 2.0));
+}
+vec2 complexReciprocal(in vec2 z){
+	return vec2(z.x / complexMag(z), -z.y / complexMag(z));
+}
+vec2 complexDiv(in vec2 a,in vec2 b){
+	return complexMult(a, complexReciprocal(b));
+}
+vec2 complexPower(in vec2 a, in vec2 b){
+	return complexExp( complexMult(b,complexLog(a))  );
+}
+//Misc Functions:
+float nearestPower(in float a, in float base){
+	return pow(base,  ceil(  log(abs(a))/log(base)  )-1.0 );
+}
+float map(float value, float istart, float istop, float ostart, float ostop) {
+	   return ostart + (ostop - ostart) * ((value - istart) / (istop - istart));
+}
+
+void main( void ){
+
+	//SHIFT AND SCALE COORDINATES
+	vec2 uv=gl_FragCoord.xy/sketchSize.xy - off;
+
+	//ESCHER GRID TRANSFORM:
+	float factor = pow(1.0/scale,Branches);
+	uv= complexPower(uv, complexDiv(vec2( log(factor) ,TWO_PI), vec2(0.0,TWO_PI) ) );
+
+	//RECTANGULAR DROSTE EFFECT:
+	float FT = fract(globalTime);
+	FT = log(FT+1.)/log(2.);
+	uv *= 1.0+FT*(scale-1.0);
+
+  float npower = max(nearestPower(uv.x,scale),nearestPower(uv.y,scale));
+	uv.x = map(uv.x,-npower,npower,-1.0,1.0);
+	uv.y = map(uv.y,-npower,npower,-1.0,1.0);
+
+	//UNDO SHIFT AND SCALE:
+	gl_FragColor =  texture(texture,uv*off+vec2(off));
+}

processing_app/library/glvideo/droste.rb

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+load_library :glvideo
+include_package 'gohai.glvideo'
+attr_reader :cam, :my_filter, :origin
+
+def settings
+  size(1280, 960, P2D)
+end
+
+def setup
+  sketch_title 'Droste'
+  @origin = Time.now
+  @my_filter = load_shader(data_path('droste.glsl'))
+  my_filter.set('sketchSize', width.to_f, height.to_f)
+  start_capture
+end
+
+def time
+  (Time.now - origin) * 0.5
+end
+
+def start_capture
+  @cam = GLCapture.new(self)
+  cam.start
+end
+
+def draw
+  background 0
+  cam.read if cam.available
+  image(cam, 0, 0, width, height)
+  my_filter.set('globalTime', time)
+  return if mouse_pressed?
+  filter(my_filter)
+end