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225 lines
11 KiB
Plaintext
225 lines
11 KiB
Plaintext
#version 450
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/*
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Simplified, Traced Minkowski Tube.
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----------------------------------
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This was inspired by Shadertoy user Akaitora's "Worley Tunnel" which you can find here:
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https://www.shadertoy.com/view/XtjSzR
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Akaitora had a question, but I didn't have room to answer, so this is for anyone who's interested
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in understanding the reasoning behind the oldschool tunnel effect. I see a "lot" of them around.
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I'll assume most know that the endless tunnel effect is a simplification of a raytraced,
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cylindrically-mapped inner cylinder. Without going into detail, by restricting the "XY" coordinates
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of the ray origin (camera position) "ro" to zero, the ray intersection equation becomes almost
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trivial. For a 3D unit ray-direction vector, "rd," the solution is something along the lines of:
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float distance = 1./length(rd.xy);
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The 3D surface point is then: sp = vec3(0., 0., ro.z) + rd/length(rd.xy); // Where "ro.z" is time.
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The surface point coordinates enable you to color the surface using a 3D method, or in the case of
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the endless tunnel effect, cylindrically map a texture, or texture-function, (preferably seamless)
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onto the surface:
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vec3 color = TexFunction(vec3 sp) { return texUV(scaleU*atan(sp.y, sp.x)/6.2832, scaleV*sp.z); }
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You can see that "sp.z" is equal to: ro.z(time)*scaleV + rd.z*scaleV(constant)/length(rd.xy);
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The light attenuation is usually a scaled inverse of the distance, or "k*length(rd.xy)" and the
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normal vector is about as straight forward as it gets: normalize(vec3(-sp.xy, 0.));
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Anyway, to save cycles, 1990s demo coders threw out the 3D surface information, bypassed the
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normalization of the ray-direction vector, and a bunch of other stuff, until there was virtually
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nothing left to calculate other than the texture coordinates and distance attenuation.
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The point is, for the price of just a few extra lines and almost no extra effort on the part of the
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GPU, you could have a 3D "lit" tunnel, which is more visually enticing. Like the oldschool tunnel
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demos, you could also have square, rounded square tunnels, etc.
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Hence, this simple demonstration. It's a point lit, rounded square tunnel, produced without the use
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of raymarching. As a point of interest that's probably not interesting, there's not a single "for
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loop" or "if statement" used in the code. Do I get points for that? :)
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If you ignore the 3D Voronesque function (which I'll explain another time), bump mapping, amateur
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camera movement and extra lighting, there's barely any code here. In fact, I believe you could fit
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a 3D lit, 3D-function mapped, possibly bumped, tunnel into a tweet or two... but I'll leave that to
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Fabrice Neyret, Greg Rostami, etc. ;-)
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Update: Here's a private link to a cylindrically mapped tube I put together. It's for those who'd
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like to see how to apply repeated 2D functions and textures:
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https://www.shadertoy.com/view/ltSSR1
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*/
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layout(std140, set = 0, binding = 0) uniform UBO
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{
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mat4 MVP;
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vec4 OutputSize;
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vec4 OriginalSize;
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vec4 SourceSize;
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uint FrameCount;
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} global;
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#pragma stage vertex
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layout(location = 0) in vec4 Position;
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layout(location = 1) in vec2 TexCoord;
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layout(location = 0) out vec2 vTexCoord;
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const vec2 madd = vec2(0.5, 0.5);
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void main()
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{
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gl_Position = global.MVP * Position;
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vTexCoord = gl_Position.xy;
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}
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#pragma stage fragment
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layout(location = 0) in vec2 vTexCoord;
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layout(location = 0) out vec4 FragColor;
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float iGlobalTime = float(global.FrameCount)*0.025;
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vec2 iResolution = global.OutputSize.xy;
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// 2D rotation. Always handy.
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mat2 rot(float th){ float cs = cos(th), si = sin(th); return mat2(cs, -si, si, cs); }
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// 3D Voronoi-like function. Cheap, low quality, 1st and 2nd order 3D Voronoi imitation.
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//
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// I wrote this a while back because I wanted a stand-alone algorithm fast enough to produce regular, or 2nd order,
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// Voronoi-looking patterns in a raymarching setting. Anyway, this is what I came up with. Obviously, it wouldn't
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// pass as genuine 3D Voronoi, but there's only so much you can do with a few lines. Even so, it has a Voronoi feel
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// to it. Hence, Voronesque.
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//
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// Here's a rough explanation of how it works: Instead of partitioning space into cubes, partition it into its
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// simplex form, namely tetrahedrons. Use the four tetrahedral vertices to create some random falloff values, then
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// pick off the two highest, or lowest, depending on perspective. That's it. If you'd like to know more, the
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// function is roughly commented, plus there's a simplex noise related link below that should make it more clear.
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//
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// Credits: Ken Perlin, the creator of simplex noise, of course. Stefan Gustavson's paper - "Simplex Noise Demystified."
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// IQ, other "ShaderToy.com" people, Brian Sharpe (does interesting work), etc.
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//
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// My favorite simplex-related write up: "Simplex Noise, keeping it simple." - Jasper Flick?
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// http://catlikecoding.com/unity/tutorials/simplex-noise/
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//
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float Voronesque( in vec3 p ){
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// Skewing the cubic grid, then determining the first vertice.
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vec3 i = floor(p + dot(p, vec3(0.333333)) ); p -= i - dot(i, vec3(0.166666)) ;
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// Breaking the skewed cube into tetrahedra with partitioning planes, then determining which side of the
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// intersecting planes the skewed point is on. Ie: Determining which tetrahedron the point is in.
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vec3 i1 = step(0., p-p.yzx), i2 = max(i1, 1.0-i1.zxy); i1 = min(i1, 1.0-i1.zxy);
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// Using the above to calculate the other three vertices. Now we have all four tetrahedral vertices.
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vec3 p1 = p - i1 + 0.166666, p2 = p - i2 + 0.333333, p3 = p - 0.5;
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vec3 rnd = vec3(7, 157, 113); // I use this combination to pay homage to Shadertoy.com. :)
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// Falloff values from the skewed point to each of the tetrahedral points.
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vec4 v = max(0.5 - vec4(dot(p, p), dot(p1, p1), dot(p2, p2), dot(p3, p3)), 0.);
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// Assigning four random values to each of the points above.
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vec4 d = vec4( dot(i, rnd), dot(i + i1, rnd), dot(i + i2, rnd), dot(i + 1., rnd) );
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// Further randomizing "d," then combining it with "v" to produce the final random falloff values. Range [0, 1]
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d = fract(sin(d)*262144.)*v*2.;
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// Reusing "v" to determine the largest, and second largest falloff values. Analogous to distance.
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v.x = max(d.x, d.y), v.y = max(d.z, d.w), v.z = max(min(d.x, d.y), min(d.z, d.w)), v.w = min(v.x, v.y);
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return max(v.x, v.y)- max(v.z, v.w); // Maximum minus second order, for that beveled Voronoi look. Range [0, 1].
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//return max(v.x, v.y); // Maximum, or regular value for the regular Voronoi aesthetic. Range [0, 1].
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}
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void mainImage( out vec4 fragColor, in vec2 fragCoord ){
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// Screen coordinates, plus some movement about the center.
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vec2 uv = (fragCoord.xy - iResolution.xy*0.5)/iResolution.y + vec2(0.5*cos(iGlobalTime*0.5), 0.25*sin(iGlobalTime*0.5));
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// Unit direction ray.
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vec3 rd = normalize(vec3(uv, 1.));
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rd.xy *= rot(sin(iGlobalTime*0.25)*0.5); // Very subtle look around, just to show it's a 3D effect.
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rd.xz *= rot(sin(iGlobalTime*0.25)*0.5);
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// Screen color. Initialized to black.
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vec3 col = vec3(0);
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// Ray intersection of a cylinder (radius one) - centered at the origin - from a ray-origin that has XY coordinates
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// also centered at the origin.
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//float sDist = max(dot(rd.xy, rd.xy), 1e-16); // Analogous to the surface function.
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//sDist = 1./sqrt(sDist); // Ray origin to surface distance.
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// Same as above, but using a Minkowski distance and scaling factor. I tried it on a whim, and it seemed to work.
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// I know, not scientific at all, but it kind of makes sense. They'll let anyone get behind a computer these days. :)
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vec2 scale = vec2(0.75, 1.);
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float power = 6.;
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float sDist = max(dot( pow(abs(rd.xy)*scale, vec2(power)), vec2(1.) ), 1e-16); // Analogous to the surface function.
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sDist = 1./pow( sDist, 1./power ); // Ray origin to surface distance.
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//if(sDist>1e-8){
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// Using the the distance "sDist" above to calculate the surface position. Ie: sp = ro + rd*t;
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// I've hardcoded "ro" to reduce line count. Note that "ro.xy" is centered on zero. The cheap
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// ray-intersection formula above relies on that.
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vec3 sp = vec3(0.0, 0.0, iGlobalTime*2.) + rd*sDist;
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// The surface normal. Based on the derivative of the surface description function. See above.
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//vec3 sn = normalize(vec3(-sp.xy, 0.)); // Cylinder normal.
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vec3 sn = normalize(-sign(sp)*vec3(pow(abs(sp.xy)*scale, vec2(power-1.)), 0.)); // Minkowski normal.
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// Bump mapping.
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//
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// I wanted to make this example as simple as possible, but it's only a few extra lines. Note the larger
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// "eps" number. Increasing the value spreads the samples out, which effectively blurs the result, thus
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// reducing the jaggies. The downside is loss of bump precision, which isn't noticeable in this particular
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// example. Decrease the value to "0.001" to see what I'm talking about.
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const vec2 eps = vec2(0.025, 0.);
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float c = Voronesque(sp*2.5); // Base value. Used below to color the surface.
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// 3D gradient vector... of sorts. Based on the bump function. In this case, Voronoi.
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vec3 gr = (vec3(Voronesque((sp-eps.xyy)*2.5), Voronesque((sp-eps.yxy)*2.5), Voronesque((sp-eps.yyx)*2.5))-c)/eps.x;
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gr -= sn*dot(sn, gr); // There's a reason for this... but I need more room. :)
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sn = normalize(sn + gr*0.1); // Combining the bump gradient vector with the object surface normal.
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// Lighting.
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//
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// The light is hovering just in front of the viewer.
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vec3 lp = vec3(0.0, 0.0, iGlobalTime*2. + 3.);
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vec3 ld = lp - sp; // Light direction.
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float dist = max(length(ld), 0.001); // Distance from light to the surface.
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ld /= dist; // Use the distance to normalize "ld."
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// Light attenuation, based on the distance above.
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float atten = min(1.0/max(0.75 + dist*0.25 + dist*dist*0.05, 0.001), 1.0);
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float diff = max(dot(sn, ld), 0.); // Diffuse light value.
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float spec = pow(max(dot(reflect(-ld, sn), -rd), 0.), 16.); // Specular highlighting.
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// Adding some fake, reflective environment information.
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float ref = Voronesque((sp + reflect(rd, sn)*0.5)*2.5);
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// Coloring the surface with the Voronesque function that is used to bump the surface. See "bump mapping" above.
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vec3 objCol = vec3(min(c*1.5, 1.), pow(c, 2.5), pow(c, 12.)); // Cheap, but effective, red palette.
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//vec3 objCol = vec3(c*c*0.9, c, c*c*0.4); // Cheap green palette.
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//vec3 objCol = vec3(pow(c, 1.6), pow(c, 1.7), c); // Purpley blue.
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//vec3 objCol = vec3(c); // Grey scale.
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// Using the values above to produce the final color.
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//col = (objCol*(diff + ref*0.25 + 0.25) + vec3(1., 0.8, 0.9)*ref*0.25 + spec*vec3(0.75, 0.9, 1.))*atten;
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col = (objCol*(vec3(1.0, 0.97, 0.92)*diff + ref*0.5 + 0.25) + vec3(1., 0.8, 0.9)*ref*0.3 + vec3(1., 0.9, 0.7)*spec)*atten;
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//col = ((vec3(1.0, 0.97, 0.92)*diff + ref*0.5 + 0.25)*c + vec3(1., 0.8, 0.9)*ref*0.3 + vec3(0.75, 0.9, 1.)*spec)*atten;
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//}
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fragColor = vec4(min(col, 1.), 1.);
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}
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void main(void)
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{
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//just some shit to wrap shadertoy's stuff
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vec2 FragCoord = vTexCoord.xy*global.OutputSize.xy;
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FragCoord.y = -FragCoord.y;
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mainImage(FragColor,FragCoord);
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} |