Force resolution: Variable 800x450 (16:9) 1600x900 (16:9 for big screens) 1920x1080 (for fullscreen testing?)

Other global variables:

uniform vec2 iResolution; // screen size in pixels. note: in Shader Toy this is vec3
uniform float iTime; // time since beginning, in seconds
uniform float iTimeDelta; // time since last frame, in seconds
uniform sampler2D iChannel0; // 2D, 3D or cubemap depending on selected input
// likewise iChannel1, 2, 3

Tabs which don't compile are highlighted red, and the viewport keeps running the last version which compiled.
Sorry for no syntax highlighting!

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Title:
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Your shader as JSON for copy-pasting:
{"inputs":{"fba": ["fba","null","null","null"],"fbb":["null","null","null","null"],"fbc": ["null","null","null","null"],"fbd": ["null","null","null","null"],"image": ["fba","fbb","null","null"]},"settings":{"fba":{"coords":"pixel"},"fbb": {"coords":"pixel"},"fbc":{"coords":"pixel"},"fbd": {"coords":"pixel"},"image":{"coords":"pixel"}},"code":{"fba":"const float REPEAT=3.;\nfloat rotShape(vec2 p, float t, float shape){\nif(shape<.5) return 1.-step(.25,length(p-vec2(cos(t),sin(t))*.25));\nelse{\nvec2 q=abs(p*rot(shape*6.28+iTime)-vec2(cos(t),sin(t))*.25);\nreturn 1.-step(.25,max(q.x,q.y));}\n}\nvoid mainImage(out vec4 color, in vec2 position) { \nvec2 n_uv=position/iResolution.xy;\nvec2 uv=n_uv*vec2(iResolution.x/iResolution.y,1.)-vec2(iResolution.x/ iResolution.y,1.)*.5;\nuv*=rot(-iTime*.3);\nuv=vec2(atan(uv.y,uv.x)*2./ TAU,log(length(uv)));\nfloat t=iTime*2.3;\n\nfloat i_t=floor(t);\nfloat f_t=fract(t);\n\nvec2 i_uv=floor(uv*REPEAT);\nvec2 f_uv=fract(uv*REPEAT+vec2(0.,1.)*mod(i_uv.x+i_t,2.)*f_t);\nfloat ra=hash12(floor(uv*REPEAT+vec2(0.,1.)*mod(i_uv.x+i_t,2.)*f_t));\n\nvec3 col=vec3(\nrotShape(f_uv-vec2(.5),t*1.2,ra),\nrotShape(f_uv- vec2(.5),t*1.5,ra),\nrotShape(f_uv-vec2(.5),t*1.8,ra)\n); \ncol*=mat3(\nvec3(.1,.7,-.2),\nvec3(.1,.8,.1),\nvec3(.9,.1,.5)\n); \ncolor.rgb=mix(texture(iChannel0, n_uv).rgb,col,.2);\ncolor.a=0.0; // added by immibis after you left the camp early, to fix undefined behavior / screen corruption\n}\n","fbb":"float box(vec3 p){\nvec3 q=abs(p);\nreturn max(q.x,max(q.y,q.z));\n}\nfloat map(vec3 p){\nreturn box(p)-.1;\n}\nvoid mainImage(out vec4 color, in vec2 position) {\nvec2 uv=(position/iResolution.xy)*vec2(iResolution.x/iResolution.y,1.)- vec2(iResolution.x/iResolution.y,1.)*.5;\nvec3 ro=vec3(0,0,-4);\nvec3 rd=normalize(vec3(uv,-1)-ro);\n\nfloat t=iTime*2.3;\n\nfloat i_t=floor(t);\nfloat f_t=fract(t);\n\nfloat hit;\nfloat total_di;\nvec3 po;\nfor(int i=0; i<64; i++){\npo=ro+rd+total_di;\npo.xz*=rot(t*.4);\npo.zy*=rot(t*.7);\nfloat di=map(po);\ntotal_di+=di;\nif(di<EP){\nhit=1.;\nbreak; \n}\nif(total_di>999.){\nbreak;\n}\n}\n\nvec3 no=vec3(\nmap(po-vec3(EP,0,0))-map(po+vec3(EP,0,0)),\nmap(po- vec3(0,EP,0))-map(po+vec3(0,EP,0)),\nmap(po-vec3(0,0,EP))- map(po+vec3(0,0,EP)));no=normalize(no);\ncolor.rgb=vec3(hit); \n}","fbc":"","fbd":"","image":"const vec2 unit=vec2(.0015,.0);\nvoid mainImage(out vec4 color, in vec2 position) {\nvec2 n_uv=position/iResolution.xy;\nvec2 uv=n_uv*vec2(iResolution.x/iResolution.y,1.)-vec2(iResolution.x/ iResolution.y,1.)*.5;\n\n//n_uv.x += sin(n_uv.y*8.-iTime*3.)*.001;\n\nvec4 neighbor=\ntexture(iChannel0, n_uv+unit.xy)+\ntexture(iChannel0, n_uv+unit.yx)+\ntexture(iChannel0, n_uv-unit.xy)+\ntexture(iChannel0, n_uv-unit.yx)\n;\nvec4 here=texture(iChannel0, n_uv);\ncolor=mix(here,vec4(1)-here,pow(length(neighbor-here*4.),.5)); \ncolor.rgb=pow(color.rgb,vec3(.454545));\n\n//color=texture(iChannel1, n_uv);\n}\n","common":"const float PI=3.1415926;\nconst float TAU=2.*PI;\nconst float EP=.0015;\nfloat hash12(vec2 p)\n{\n\tvec3 p3 = fract(vec3(p.xyx) * .1031);\n p3 += dot(p3, p3.yzx + 33.33);\n return fract((p3.x + p3.y) * p3.z);\n}\nmat2 rot(float a){return mat2(cos(a),-sin(a),sin(a),cos(a));}"}}

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