optozorax/miniquad_shader_1.rs

## miniquad_shader_1.rs
/*

    Shader: https://www.shadertoy.com/view/4ljGRd
    Post: https://t.me/optozorax_dev/62
    Sorry for shitcode, this is just test
    Based on `quad` example in miniquad

*/

use miniquad::*;

#[repr(C)]
struct Vec2 {
    x: f32,
    y: f32,
}
#[repr(C)]
struct Vertex {
    pos: Vec2,
    uv: Vec2,
}

struct Stage {
    pipeline: Pipeline,
    bindings: Bindings,
    time: f64,
}

impl Stage {
    pub fn new(ctx: &mut Context) -> Stage {
        #[rustfmt::skip]
        let vertices: [Vertex; 4] = [
            Vertex { pos : Vec2 { x: -1.0, y:  1.0 }, uv: Vec2 { x: 0., y: 0. } },
            Vertex { pos : Vec2 { x:  1.0, y:  1.0 }, uv: Vec2 { x: 1., y: 0. } },
            Vertex { pos : Vec2 { x:  1.0, y: -1.0 }, uv: Vec2 { x: 1., y: 1. } },
            Vertex { pos : Vec2 { x: -1.0, y: -1.0 }, uv: Vec2 { x: 0., y: 1. } },
        ];
        let vertex_buffer = Buffer::immutable(ctx, BufferType::VertexBuffer, &vertices);

        let indices: [u16; 6] = [0, 1, 2, 0, 2, 3];
        let index_buffer = Buffer::immutable(ctx, BufferType::IndexBuffer, &indices);

        let pixels: [u8; 4 * 4 * 4] = [
            0xFF, 0xFF, 0xFF, 0xFF, 0xFF, 0x00, 0x00, 0xFF, 0xFF, 0xFF, 0xFF, 0xFF, 0xFF, 0x00,
            0x00, 0xFF, 0xFF, 0x00, 0x00, 0xFF, 0xFF, 0xFF, 0xFF, 0xFF, 0xFF, 0x00, 0x00, 0xFF,
            0xFF, 0xFF, 0xFF, 0xFF, 0xFF, 0xFF, 0xFF, 0xFF, 0xFF, 0x00, 0x00, 0x00, 0xFF, 0xFF,
            0xFF, 0xFF, 0xFF, 0x00, 0x00, 0xFF, 0xFF, 0x00, 0x00, 0xFF, 0xFF, 0xFF, 0xFF, 0xFF,
            0xFF, 0x00, 0x00, 0xFF, 0xFF, 0xFF, 0xFF, 0xFF,
        ];
        let texture = Texture::from_rgba8(ctx, 4, 4, &pixels);

        let bindings = Bindings {
            vertex_buffers: vec![vertex_buffer],
            index_buffer,
            images: vec![texture],
        };

        let shader = Shader::new(ctx, shader::VERTEX, shader::FRAGMENT, shader::META);

        let pipeline = Pipeline::new(
            ctx,
            &[BufferLayout::default()],
            &[
                VertexAttribute::new("pos", VertexFormat::Float2),
                VertexAttribute::new("uv", VertexFormat::Float2),
            ],
            shader,
        );

        Stage { pipeline, bindings, time: -1.0 }
    }
}

impl EventHandler for Stage {
    fn update(&mut self, _ctx: &mut Context) { }

    #[allow(clippy::float_cmp)]
    fn draw(&mut self, ctx: &mut Context) {
        if self.time == -1.0 {
            self.time = date::now();
        }
        let t = (date::now() - self.time) * 10.0;

        ctx.begin_default_pass(Default::default());

        ctx.apply_pipeline(&self.pipeline);
        ctx.apply_bindings(&self.bindings);

        let size = ctx.screen_size();
        let scale = 0.6;
        ctx.apply_uniforms(&shader::Uniforms {
            iResolution: (scale * size.0 / (size.1.max(size.0)), -scale * size.1 / (size.1.max(size.0)), 0.0),
            iTime: t as f32,
        });
        ctx.draw(0, 6, 1);
        ctx.end_render_pass();

        ctx.commit_frame();
    }
}

fn main() {
    miniquad::start(conf::Conf::default(), |mut ctx| {
        UserData::owning(Stage::new(&mut ctx), ctx)
    });
}

mod shader {
    use miniquad::*;

    pub const VERTEX: &str = r#"#version 100
    attribute vec2 pos;
    attribute vec2 uv;

    varying lowp vec2 texcoord;

    void main() {
        gl_Position = vec4(pos, 0, 1);
        texcoord = uv;
    }"#;

    pub const FRAGMENT: &str = r#"#version 100

    precision highp float;

    varying lowp vec2 texcoord;
    //uniform sampler2D tex;

    uniform vec3 iResolution;
    uniform float iTime;
    //uniform vec4 iMouse;

    // Ray tracing is a topic I have always wanted to explore, but never really had
    // the opportunity to do so until now. What exactly is ray tracing? Consider a
    // lamp hanging from the ceiling. Light is constantly being emitted from the
    // lamp in the form of light rays, which bounce around the room until they hit
    // your eye. Ray tracing follows a similar concept by simulating the path of
    // light through a scene, except in reverse. There is no point in doing the math
    // for light rays you cannot see!

    // Algorithmically, ray tracing is very elegant. For each pixel, shoot a light
    // ray from the camera through each pixel on screen. If the ray collides with
    // geometry in the scene, create new rays that perform the same process for both
    // reflection, as in a mirror, and refraction, as in through water. Repeat
    // to your satisfaction.

    // Having worked extensively with OpenCL in the past, this seemed like a good
    // candidate to port to a parallel runtime on a GPU. Inspired by the [smallpt](http://www.kevinbeason.com/smallpt/#moreinfo)
    // line-by-line explanation, I decided to write a parallel ray tracer with
    // extensive annotations. The results are below ...

    // ![screenshot](/uploads/raytracer.png)

    // I start with a simple ray definition, consisting of an origin point and a
    // direction vector. I also define a directional light to illuminate my scene.
    struct Ray {
        vec3 origin;
        vec3 direction;
    };

    struct Light {
        vec3 color;
        vec3 direction;
    };

    // In real life, objects have many different material properties. Some objects
    // respond very differently to light than others. For instance, a sheet of paper
    // and a polished mirror. The former exhibits a strong *diffuse* response;
    // incoming light is reflected at many angles. The latter is an example of a
    // *specular* response, where incoming light is reflected in a single direction.
    // To model this, I create a basic material definition. Objects in my scene
    // share a single (RGB) color with diffuse and specular weights.
    struct Material {
        vec3 color;
        float diffuse;
        float specular;
    };

    // To render the scene, I need to know where a ray intersects with an object.
    // Since rays have infinite length from an origin, I can model the point of
    // intersection by storing the distance along the ray. I also need to store the
    // surface normal so I know which way to bounce! Once I create a ray, it loses
    // the concept of scene geometry, so one more thing I do is forward the surface
    // material properties.
    struct Intersect {
        float len;
        vec3 normal;
        Material material;
    };

    // The last data structures I create are for objects used to fill my scene. The
    // most basic object I can model is a sphere, which is defined as a radius at
    // some center position, with some material properties. To draw the floor, I
    // also define a simple horizontal plane centered at the origin, with a normal
    // vector pointing upwards.
    struct Sphere {
        float radius;
        vec3 position;
        Material material;
    };

    struct Plane {
        vec3 normal;
        Material material;
    };

    // At this point, I define some global variables. A more advanced program might
    // pass these values in as uniforms, but for now, this is easier to tinker with.
    // Due to floating point precision errors, when a ray intersects geometry at a
    // surface, the point of intersection could possibly be just below the surface.
    // The subsequent reflection ray would then bounce off the *inside* wall of the
    // surface. This is known as self-intersection. When creating new rays, I
    // initialize them at a slightly offset origin to help mitigate this problem.
    const float epsilon = 1e-3;

    // The classical ray tracing algorithm is recursive. However, GLSL does not
    // support recursion, so I instead use an iterative approach to control the
    // number of light bounces.
    const int iterations = 16;

    // Next, I define an exposure time and gamma value. At this point, I also create
    // a basic directional light and define the ambient light color; the color here
    // is mostly a matter of taste. Basically ... lighting controls.
    const float exposure = 1e-2;
    const float gamma = 2.2;
    const float intensity = 100.0;
    const vec3 ambient = vec3(0.6, 0.8, 1.0) * intensity / gamma;

    // For a Static Light
    Light light = Light(vec3(1.0) * intensity, normalize(vec3(-1.0, 0.75, 1.0)));

    // For a Rotating Light
    // Light light = Light(vec3(1.0) * intensity, normalize(
    //                vec3(-1.0 + 4.0 * cos(iTime), 4.75,
    //                      1.0 + 4.0 * sin(iTime))));

    // I strongly dislike this line. I needed to know when a ray hits or misses a
    // surface. If it hits geometry, I returned the point at the surface. Otherwise,
    // the ray misses all geometry and instead hits the sky box. In a language that
    // supports dynamic return values, I could `return false`, but that is not an
    // option in GLSL. In the interests of making progress, I created an intersect
    // of distance zero to represent a miss and moved on.
    const Intersect miss = Intersect(0.0, vec3(0.0), Material(vec3(0.0), 0.0, 0.0));

    // As indicated earlier, I implement ray tracing for spheres. I need to compute
    // the point at which a ray intersects with a sphere. [Line-Sphere](http://en.wikipedia.org/wiki/Line-sphere_intersection)
    // intersection is relatively straightforward. For reflection purposes, a ray
    // either hits or misses, so I need to check for no solutions, or two solutions.
    // In the latter case, I need to determine which solution is "in front" so I can
    // return an intersection of appropriate distance from the ray origin.
    Intersect intersect(Ray ray, Sphere sphere) {
        // Check for a Negative Square Root
        vec3 oc = sphere.position - ray.origin;
        float l = dot(ray.direction, oc);
        float det = pow(l, 2.0) - dot(oc, oc) + pow(sphere.radius, 2.0);
        if (det < 0.0) return miss;

        // Find the Closer of Two Solutions
                 float len = l - sqrt(det);
        if (len < 0.0) len = l + sqrt(det);
        if (len < 0.0) return miss;
        return Intersect(len, (ray.origin + len*ray.direction - sphere.position) / sphere.radius, sphere.material);
    }

    // Since I created a floor plane, I likewise have to handle reflections for
    // planes by implementing [Line-Plane](http://en.wikipedia.org/wiki/Line-plane_intersection)
    // intersection. I only care about the intersect for the purposes of reflection,
    // so I only check if the quotient is non-zero.
    Intersect intersect(Ray ray, Plane plane) {
        float len = -dot(ray.origin, plane.normal) / dot(ray.direction, plane.normal);
        if (len < 0.0) return miss;
        return Intersect(len, plane.normal, plane.material);
    }

    // In a *real* ray tracing renderer, geometry would be passed in from the host
    // as a mesh containing vertices, normals, and texture coordinates, but for the
    // sake of simplicity, I hand-coded the scene-graph. In this function, I take an
    // input ray and iterate through all geometry to determine intersections.
    Intersect trace(Ray ray) {
        const int num_spheres = 3;
        Sphere spheres[num_spheres];

        // I initially started with the [smallpt](www.kevinbeason.com/smallpt/)
        // scene definition, but soon found performance was abysmal on very large
        // spheres. I kept the general format, modified to fit my data structures.

        spheres[0] = Sphere(2.0, vec3(-4.0, 3.0 + sin(iTime), 0), Material(vec3(1.0, 0.0, 0.2), 1.0, 0.001));
        spheres[1] = Sphere(3.0, vec3( 4.0 + cos(iTime), 3.0, 0), Material(vec3(0.0, 0.2, 1.0), 1.0, 0.0));
        spheres[2] = Sphere(1.0, vec3( 0.5, 1.0, 6.0),                  Material(vec3(1.0, 1.0, 1.0), 0.5, 0.25));

        // Since my ray tracing approach involves drawing to a 2D quad, I can no
        // longer use the OpenGL Depth and Stencil buffers to control the draw
        // order. Drawing is therefore sensitive to z-indexing, so I first intersect
        // with the plane, then loop through all spheres back-to-front.

        Intersect intersection = miss;
        Intersect plane = intersect(ray, Plane(vec3(0, 1, 0), Material(vec3(1.0, 1.0, 1.0), 1.0, 0.0)));
        if (plane.material.diffuse > 0.0 || plane.material.specular > 0.0) { intersection = plane; }
        for (int i = 0; i < num_spheres; i++) {
            Intersect sphere = intersect(ray, spheres[i]);
            if (sphere.material.diffuse > 0.0 || sphere.material.specular > 0.0)
                intersection = sphere;
        }
        return intersection;
    }

    // This is the critical part of writing a ray tracer. I start with some empty
    // scratch vectors for color data and the Fresnel factor. I trace the scene with
    // using an input ray, and continue to fire new rays until the iteration depth
    // is reached, at which point I return the total sum of the color values from
    // computed at each bounce.
    vec3 radiance(Ray ray) {
        vec3 color = vec3(0.0), fresnel = vec3(0.0);
        vec3 mask = vec3(1.0);
        for (int i = 0; i <= iterations; ++i) {
            Intersect hit = trace(ray);

            // This goes back to the dummy "miss" intersect. Basically, if the scene
            // trace returns an intersection with either a diffuse or specular
            // coefficient, then it has encountered a surface of a sphere or plane.
            // Otherwise, the current ray has reached the ambient-colored sky box.

            if (hit.material.diffuse > 0.0 || hit.material.specular > 0.0) {

                // Here I use the [Schlick Approximation](http://en.wikipedia.org/wiki/Schlick's_approximation)
                // to determine the Fresnel specular contribution factor, a measure
                // of how much incoming light is reflected or refracted. I compute
                // the Fresnel term and use a mask to track the fraction of
                // reflected light in the current ray with respect to the original.

                vec3 r0 = hit.material.color.rgb * hit.material.specular;
                float hv = clamp(dot(hit.normal, -ray.direction), 0.0, 1.0);
                fresnel = r0 + (1.0 - r0) * pow(1.0 - hv, 5.0);
                mask *= fresnel;

                // I handle shadows and diffuse colors next. I condensed this part
                // into one conditional evaluation for brevity. Remember `epsilon`?
                // I use it to trace a ray slightly offset from the point of
                // intersection to the light source. If the shadow ray does not hit
                // an object, it will be a "miss" as it hits the skybox. This means
                // there are no objects between the point and the light, at which
                // point I can add the diffuse color to the fragment color since the
                // object is not in shadow.

                if (trace(Ray(ray.origin + hit.len * ray.direction + epsilon * light.direction, light.direction)) == miss) {
                    color += clamp(dot(hit.normal, light.direction), 0.0, 1.0) * light.color
                           * hit.material.color.rgb * hit.material.diffuse
                           * (1.0 - fresnel) * mask / fresnel;
                }

                // After computing diffuse colors, I then generate a new reflection
                // ray and overwrite the original ray that was passed in as an
                // argument to the radiance(...) function. Then I repeat until I
                // reach the iteration depth.

                vec3 reflection = reflect(ray.direction, hit.normal);
                ray = Ray(ray.origin + hit.len * ray.direction + epsilon * reflection, reflection);

            } else {

                // This is the other half of the tracing branch. If the trace failed
                // to return an intersection with an attached material, then it is
                // safe to assume that the ray points at the sky, or out of bounds
                // of the scene. At this point I realized that real objects have a
                // small sheen to them, so I hard-coded a small spotlight pointing
                // in the same direction as the main light for pseudo-realism.

                vec3 spotlight = vec3(1e6) * pow(abs(dot(ray.direction, light.direction)), 250.0);
                color += mask * (ambient + spotlight); break;
            }
        }
        return color;
    }

    // The main function primarily deals with organizing data from OpenGL into a
    // format that the ray tracer can use. For ray tracing, I need to fire a ray for
    // each pixel, or more precisely, a ray for every fragment. However, pixels to
    // fragment coordinates do not map one a one-to-one basis, so I need to divide
    // the fragment coordinates by the viewport resolution. I then offset that by a
    // fixed value to re-center the coordinate system.

    void main() {
        vec2 fragCoord = texcoord;
        vec2 uv    = fragCoord.xy / iResolution.xy + vec2(-0.8, 1);
        uv.x *= -iResolution.x / iResolution.y;
        uv.y *= -iResolution.y / iResolution.x;

        // For each fragment, create a ray at a fixed point of origin directed at
        // the coordinates of each fragment. The last thing before writing the color
        // to the fragment is to post-process the pixel values using tone-mapping.
        // In this case, I adjust for exposure and perform linear gamma correction.

        Ray ray = Ray(vec3(0.0, 2.5, 12.0), normalize(vec3(uv.x, uv.y, -1.0)));
        gl_FragColor = vec4(pow(radiance(ray) * exposure, vec3(1.0 / gamma)), 1.0);
    }
    "#;

    pub const META: ShaderMeta = ShaderMeta {
        images: &[],
        uniforms: UniformBlockLayout {
            uniforms: &[
                ("iResolution", UniformType::Float3),
                ("iTime", UniformType::Float1),
            ],
        },
    };

    #[allow(non_snake_case)]
    #[repr(C)]
    pub struct Uniforms {
        pub iResolution: (f32, f32, f32),
        pub iTime: f32,
    }
}
	/*

	Shader: https://www.shadertoy.com/view/4ljGRd
	Post: https://t.me/optozorax_dev/62
	Sorry for shitcode, this is just test
	Based on `quad` example in miniquad

	*/

	use miniquad::*;

	#[repr(C)]
	struct Vec2 {
	x: f32,
	y: f32,
	}
	#[repr(C)]
	struct Vertex {
	pos: Vec2,
	uv: Vec2,
	}

	struct Stage {
	pipeline: Pipeline,
	bindings: Bindings,
	time: f64,
	}

	impl Stage {
	pub fn new(ctx: &mut Context) -> Stage {
	#[rustfmt::skip]
	let vertices: [Vertex; 4] = [
	Vertex { pos : Vec2 { x: -1.0, y: 1.0 }, uv: Vec2 { x: 0., y: 0. } },
	Vertex { pos : Vec2 { x: 1.0, y: 1.0 }, uv: Vec2 { x: 1., y: 0. } },
	Vertex { pos : Vec2 { x: 1.0, y: -1.0 }, uv: Vec2 { x: 1., y: 1. } },
	Vertex { pos : Vec2 { x: -1.0, y: -1.0 }, uv: Vec2 { x: 0., y: 1. } },
	];
	let vertex_buffer = Buffer::immutable(ctx, BufferType::VertexBuffer, &vertices);

	let indices: [u16; 6] = [0, 1, 2, 0, 2, 3];
	let index_buffer = Buffer::immutable(ctx, BufferType::IndexBuffer, &indices);

	let pixels: [u8; 4 * 4 * 4] = [
	0xFF, 0xFF, 0xFF, 0xFF, 0xFF, 0x00, 0x00, 0xFF, 0xFF, 0xFF, 0xFF, 0xFF, 0xFF, 0x00,
	0x00, 0xFF, 0xFF, 0x00, 0x00, 0xFF, 0xFF, 0xFF, 0xFF, 0xFF, 0xFF, 0x00, 0x00, 0xFF,
	0xFF, 0xFF, 0xFF, 0xFF, 0xFF, 0xFF, 0xFF, 0xFF, 0xFF, 0x00, 0x00, 0x00, 0xFF, 0xFF,
	0xFF, 0xFF, 0xFF, 0x00, 0x00, 0xFF, 0xFF, 0x00, 0x00, 0xFF, 0xFF, 0xFF, 0xFF, 0xFF,
	0xFF, 0x00, 0x00, 0xFF, 0xFF, 0xFF, 0xFF, 0xFF,
	];
	let texture = Texture::from_rgba8(ctx, 4, 4, &pixels);

	let bindings = Bindings {
	vertex_buffers: vec![vertex_buffer],
	index_buffer,
	images: vec![texture],
	};

	let shader = Shader::new(ctx, shader::VERTEX, shader::FRAGMENT, shader::META);

	let pipeline = Pipeline::new(
	ctx,
	&[BufferLayout::default()],
	&[
	VertexAttribute::new("pos", VertexFormat::Float2),
	VertexAttribute::new("uv", VertexFormat::Float2),
	],
	shader,
	);

	Stage { pipeline, bindings, time: -1.0 }
	}
	}

	impl EventHandler for Stage {
	fn update(&mut self, _ctx: &mut Context) { }

	#[allow(clippy::float_cmp)]
	fn draw(&mut self, ctx: &mut Context) {
	if self.time == -1.0 {
	self.time = date::now();
	}
	let t = (date::now() - self.time) * 10.0;

	ctx.begin_default_pass(Default::default());

	ctx.apply_pipeline(&self.pipeline);
	ctx.apply_bindings(&self.bindings);

	let size = ctx.screen_size();
	let scale = 0.6;
	ctx.apply_uniforms(&shader::Uniforms {
	iResolution: (scale * size.0 / (size.1.max(size.0)), -scale * size.1 / (size.1.max(size.0)), 0.0),
	iTime: t as f32,
	});
	ctx.draw(0, 6, 1);
	ctx.end_render_pass();

	ctx.commit_frame();
	}
	}

	fn main() {
	miniquad::start(conf::Conf::default(), \|mut ctx\| {
	UserData::owning(Stage::new(&mut ctx), ctx)
	});
	}

	mod shader {
	use miniquad::*;

	pub const VERTEX: &str = r#"#version 100
	attribute vec2 pos;
	attribute vec2 uv;

	varying lowp vec2 texcoord;

	void main() {
	gl_Position = vec4(pos, 0, 1);
	texcoord = uv;
	}"#;

	pub const FRAGMENT: &str = r#"#version 100

	precision highp float;

	varying lowp vec2 texcoord;
	//uniform sampler2D tex;

	uniform vec3 iResolution;
	uniform float iTime;
	//uniform vec4 iMouse;

	// Ray tracing is a topic I have always wanted to explore, but never really had
	// the opportunity to do so until now. What exactly is ray tracing? Consider a
	// lamp hanging from the ceiling. Light is constantly being emitted from the
	// lamp in the form of light rays, which bounce around the room until they hit
	// your eye. Ray tracing follows a similar concept by simulating the path of
	// light through a scene, except in reverse. There is no point in doing the math
	// for light rays you cannot see!

	// Algorithmically, ray tracing is very elegant. For each pixel, shoot a light
	// ray from the camera through each pixel on screen. If the ray collides with
	// geometry in the scene, create new rays that perform the same process for both
	// reflection, as in a mirror, and refraction, as in through water. Repeat
	// to your satisfaction.

	// Having worked extensively with OpenCL in the past, this seemed like a good
	// candidate to port to a parallel runtime on a GPU. Inspired by the [smallpt](http://www.kevinbeason.com/smallpt/#moreinfo)
	// line-by-line explanation, I decided to write a parallel ray tracer with
	// extensive annotations. The results are below ...

	// ![screenshot](/uploads/raytracer.png)

	// I start with a simple ray definition, consisting of an origin point and a
	// direction vector. I also define a directional light to illuminate my scene.
	struct Ray {
	vec3 origin;
	vec3 direction;
	};

	struct Light {
	vec3 color;
	vec3 direction;
	};

	// In real life, objects have many different material properties. Some objects
	// respond very differently to light than others. For instance, a sheet of paper
	// and a polished mirror. The former exhibits a strong diffuse response;
	// incoming light is reflected at many angles. The latter is an example of a
	// specular response, where incoming light is reflected in a single direction.
	// To model this, I create a basic material definition. Objects in my scene
	// share a single (RGB) color with diffuse and specular weights.
	struct Material {
	vec3 color;
	float diffuse;
	float specular;
	};

	// To render the scene, I need to know where a ray intersects with an object.
	// Since rays have infinite length from an origin, I can model the point of
	// intersection by storing the distance along the ray. I also need to store the
	// surface normal so I know which way to bounce! Once I create a ray, it loses
	// the concept of scene geometry, so one more thing I do is forward the surface
	// material properties.
	struct Intersect {
	float len;
	vec3 normal;
	Material material;
	};

	// The last data structures I create are for objects used to fill my scene. The
	// most basic object I can model is a sphere, which is defined as a radius at
	// some center position, with some material properties. To draw the floor, I
	// also define a simple horizontal plane centered at the origin, with a normal
	// vector pointing upwards.
	struct Sphere {
	float radius;
	vec3 position;
	Material material;
	};

	struct Plane {
	vec3 normal;
	Material material;
	};

	// At this point, I define some global variables. A more advanced program might
	// pass these values in as uniforms, but for now, this is easier to tinker with.
	// Due to floating point precision errors, when a ray intersects geometry at a
	// surface, the point of intersection could possibly be just below the surface.
	// The subsequent reflection ray would then bounce off the inside wall of the
	// surface. This is known as self-intersection. When creating new rays, I
	// initialize them at a slightly offset origin to help mitigate this problem.
	const float epsilon = 1e-3;

	// The classical ray tracing algorithm is recursive. However, GLSL does not
	// support recursion, so I instead use an iterative approach to control the
	// number of light bounces.
	const int iterations = 16;

	// Next, I define an exposure time and gamma value. At this point, I also create
	// a basic directional light and define the ambient light color; the color here
	// is mostly a matter of taste. Basically ... lighting controls.
	const float exposure = 1e-2;
	const float gamma = 2.2;
	const float intensity = 100.0;
	const vec3 ambient = vec3(0.6, 0.8, 1.0) * intensity / gamma;

	// For a Static Light
	Light light = Light(vec3(1.0) * intensity, normalize(vec3(-1.0, 0.75, 1.0)));

	// For a Rotating Light
	// Light light = Light(vec3(1.0) * intensity, normalize(
	// vec3(-1.0 + 4.0 * cos(iTime), 4.75,
	// 1.0 + 4.0 * sin(iTime))));

	// I strongly dislike this line. I needed to know when a ray hits or misses a
	// surface. If it hits geometry, I returned the point at the surface. Otherwise,
	// the ray misses all geometry and instead hits the sky box. In a language that
	// supports dynamic return values, I could `return false`, but that is not an
	// option in GLSL. In the interests of making progress, I created an intersect
	// of distance zero to represent a miss and moved on.
	const Intersect miss = Intersect(0.0, vec3(0.0), Material(vec3(0.0), 0.0, 0.0));

	// As indicated earlier, I implement ray tracing for spheres. I need to compute
	// the point at which a ray intersects with a sphere. [Line-Sphere](http://en.wikipedia.org/wiki/Line-sphere_intersection)
	// intersection is relatively straightforward. For reflection purposes, a ray
	// either hits or misses, so I need to check for no solutions, or two solutions.
	// In the latter case, I need to determine which solution is "in front" so I can
	// return an intersection of appropriate distance from the ray origin.
	Intersect intersect(Ray ray, Sphere sphere) {
	// Check for a Negative Square Root
	vec3 oc = sphere.position - ray.origin;
	float l = dot(ray.direction, oc);
	float det = pow(l, 2.0) - dot(oc, oc) + pow(sphere.radius, 2.0);
	if (det < 0.0) return miss;

	// Find the Closer of Two Solutions
	float len = l - sqrt(det);
	if (len < 0.0) len = l + sqrt(det);
	if (len < 0.0) return miss;
	return Intersect(len, (ray.origin + len*ray.direction - sphere.position) / sphere.radius, sphere.material);
	}

	// Since I created a floor plane, I likewise have to handle reflections for
	// planes by implementing [Line-Plane](http://en.wikipedia.org/wiki/Line-plane_intersection)
	// intersection. I only care about the intersect for the purposes of reflection,
	// so I only check if the quotient is non-zero.
	Intersect intersect(Ray ray, Plane plane) {
	float len = -dot(ray.origin, plane.normal) / dot(ray.direction, plane.normal);
	if (len < 0.0) return miss;
	return Intersect(len, plane.normal, plane.material);
	}

	// In a real ray tracing renderer, geometry would be passed in from the host
	// as a mesh containing vertices, normals, and texture coordinates, but for the
	// sake of simplicity, I hand-coded the scene-graph. In this function, I take an
	// input ray and iterate through all geometry to determine intersections.
	Intersect trace(Ray ray) {
	const int num_spheres = 3;
	Sphere spheres[num_spheres];

	// I initially started with the [smallpt](www.kevinbeason.com/smallpt/)
	// scene definition, but soon found performance was abysmal on very large
	// spheres. I kept the general format, modified to fit my data structures.

	spheres[0] = Sphere(2.0, vec3(-4.0, 3.0 + sin(iTime), 0), Material(vec3(1.0, 0.0, 0.2), 1.0, 0.001));
	spheres[1] = Sphere(3.0, vec3( 4.0 + cos(iTime), 3.0, 0), Material(vec3(0.0, 0.2, 1.0), 1.0, 0.0));
	spheres[2] = Sphere(1.0, vec3( 0.5, 1.0, 6.0), Material(vec3(1.0, 1.0, 1.0), 0.5, 0.25));

	// Since my ray tracing approach involves drawing to a 2D quad, I can no
	// longer use the OpenGL Depth and Stencil buffers to control the draw
	// order. Drawing is therefore sensitive to z-indexing, so I first intersect
	// with the plane, then loop through all spheres back-to-front.

	Intersect intersection = miss;
	Intersect plane = intersect(ray, Plane(vec3(0, 1, 0), Material(vec3(1.0, 1.0, 1.0), 1.0, 0.0)));
	if (plane.material.diffuse > 0.0 \|\| plane.material.specular > 0.0) { intersection = plane; }
	for (int i = 0; i < num_spheres; i++) {
	Intersect sphere = intersect(ray, spheres[i]);
	if (sphere.material.diffuse > 0.0 \|\| sphere.material.specular > 0.0)
	intersection = sphere;
	}
	return intersection;
	}

	// This is the critical part of writing a ray tracer. I start with some empty
	// scratch vectors for color data and the Fresnel factor. I trace the scene with
	// using an input ray, and continue to fire new rays until the iteration depth
	// is reached, at which point I return the total sum of the color values from
	// computed at each bounce.
	vec3 radiance(Ray ray) {
	vec3 color = vec3(0.0), fresnel = vec3(0.0);
	vec3 mask = vec3(1.0);
	for (int i = 0; i <= iterations; ++i) {
	Intersect hit = trace(ray);

	// This goes back to the dummy "miss" intersect. Basically, if the scene
	// trace returns an intersection with either a diffuse or specular
	// coefficient, then it has encountered a surface of a sphere or plane.
	// Otherwise, the current ray has reached the ambient-colored sky box.

	if (hit.material.diffuse > 0.0 \|\| hit.material.specular > 0.0) {

	// Here I use the [Schlick Approximation](http://en.wikipedia.org/wiki/Schlick's_approximation)
	// to determine the Fresnel specular contribution factor, a measure
	// of how much incoming light is reflected or refracted. I compute
	// the Fresnel term and use a mask to track the fraction of
	// reflected light in the current ray with respect to the original.

	vec3 r0 = hit.material.color.rgb * hit.material.specular;
	float hv = clamp(dot(hit.normal, -ray.direction), 0.0, 1.0);
	fresnel = r0 + (1.0 - r0) * pow(1.0 - hv, 5.0);
	mask *= fresnel;

	// I handle shadows and diffuse colors next. I condensed this part
	// into one conditional evaluation for brevity. Remember `epsilon`?
	// I use it to trace a ray slightly offset from the point of
	// intersection to the light source. If the shadow ray does not hit
	// an object, it will be a "miss" as it hits the skybox. This means
	// there are no objects between the point and the light, at which
	// point I can add the diffuse color to the fragment color since the
	// object is not in shadow.

	if (trace(Ray(ray.origin + hit.len * ray.direction + epsilon * light.direction, light.direction)) == miss) {
	color += clamp(dot(hit.normal, light.direction), 0.0, 1.0) * light.color
	* hit.material.color.rgb * hit.material.diffuse
	* (1.0 - fresnel) * mask / fresnel;
	}

	// After computing diffuse colors, I then generate a new reflection
	// ray and overwrite the original ray that was passed in as an
	// argument to the radiance(...) function. Then I repeat until I
	// reach the iteration depth.

	vec3 reflection = reflect(ray.direction, hit.normal);
	ray = Ray(ray.origin + hit.len * ray.direction + epsilon * reflection, reflection);

	} else {

	// This is the other half of the tracing branch. If the trace failed
	// to return an intersection with an attached material, then it is
	// safe to assume that the ray points at the sky, or out of bounds
	// of the scene. At this point I realized that real objects have a
	// small sheen to them, so I hard-coded a small spotlight pointing
	// in the same direction as the main light for pseudo-realism.

	vec3 spotlight = vec3(1e6) * pow(abs(dot(ray.direction, light.direction)), 250.0);
	color += mask * (ambient + spotlight); break;
	}
	}
	return color;
	}

	// The main function primarily deals with organizing data from OpenGL into a
	// format that the ray tracer can use. For ray tracing, I need to fire a ray for
	// each pixel, or more precisely, a ray for every fragment. However, pixels to
	// fragment coordinates do not map one a one-to-one basis, so I need to divide
	// the fragment coordinates by the viewport resolution. I then offset that by a
	// fixed value to re-center the coordinate system.

	void main() {
	vec2 fragCoord = texcoord;
	vec2 uv = fragCoord.xy / iResolution.xy + vec2(-0.8, 1);
	uv.x *= -iResolution.x / iResolution.y;
	uv.y *= -iResolution.y / iResolution.x;

	// For each fragment, create a ray at a fixed point of origin directed at
	// the coordinates of each fragment. The last thing before writing the color
	// to the fragment is to post-process the pixel values using tone-mapping.
	// In this case, I adjust for exposure and perform linear gamma correction.

	Ray ray = Ray(vec3(0.0, 2.5, 12.0), normalize(vec3(uv.x, uv.y, -1.0)));
	gl_FragColor = vec4(pow(radiance(ray) * exposure, vec3(1.0 / gamma)), 1.0);
	}
	"#;

	pub const META: ShaderMeta = ShaderMeta {
	images: &[],
	uniforms: UniformBlockLayout {
	uniforms: &[
	("iResolution", UniformType::Float3),
	("iTime", UniformType::Float1),
	],
	},
	};

	#[allow(non_snake_case)]
	#[repr(C)]
	pub struct Uniforms {
	pub iResolution: (f32, f32, f32),
	pub iTime: f32,
	}
	}