gplib/include/gp/rendering/renderer.hpp

#pragma once

#include "gp_config.hpp"

#include "gp/algorithm/min_of.hpp"
#include "gp/allocator/buddy.hpp"
#include "gp/function.hpp"
#include "gp/indexed_array.hpp"
#include "gp/math.hpp"

using vec2 = gp::vec2_g<>;
using vec3 = gp::vec3_g<>;
using vec4 = gp::vec4_g<>;

struct camera{
	vec3 position;
	vec3 normal;
};

using index_t = size_t;
using distance_t = gp_config::rendering::default_type;
using color_t = GP_CONFIG__RENDERING__COLOR_T;

struct render_point{
	distance_t distance;
	index_t material;

	bool operator<(const render_point& rhs) {
		return distance < rhs.distance;
	}
};

using sdf_t = gp::function<render_point(vec3&)>;
using material_t = gp::function<color_t(vec3&)>;


/**
 * @brief A pure ray-marching renderer. Prints pixels on order.
 */
class renderer {
	using g_t = gp_config::rendering::default_type;
	constexpr static auto epsilon = gp_config::rendering::epsilon;
public:
	gp::indexed_array<sdf_t, 4096> scene_elements;
	gp::indexed_array<material_t, 4096> materials;
	gp::buddy<> allocator;
	material_t sky_box;
	vec2 _resolution{128,64};
	camera _camera{{0, 0, -1}, {0, 0, 0}};
	vec2 _fov{90, 45};
	distance_t projection_start = 1;
	distance_t projection_end = 50;
	size_t passes = 12;

	renderer(gp::buffer<char> allocation_buffer) 
	: allocator(allocation_buffer.begin().data, allocation_buffer.size())
	, sky_box{gp::reference_wrapper<gp::buddy<>>{allocator}}
	{}

	render_point sdf(vec3& render_target) {
		return gp::min_of(
			scene_elements.begin(), 
			scene_elements.end(),
			[&](auto& p){
				return p(render_target);
			}
		);
	}

	auto& get_allocator() {
		return allocator;
	}

	color_t render(vec2 pixel) {
		g_t depth = projection_start;
		vec3 target = _camera.normal;
		auto half_res = _resolution/vec2{2.0, 2.0};
		pixel = pixel - half_res;
		pixel = pixel / half_res;
		pixel = pixel * _fov;
		pixel = pixel / vec2{180, 180} * vec2{gp::pi<g_t>,gp::pi<g_t>};

		// Y-rot (adjusts x)
		target = vec3{
			target.x*gp::cos(pixel.x) + target.z*gp::sin(pixel.x),
			target.y,
			-target.x*gp::sin(pixel.x)+target.z*gp::cos(pixel.x)
		};
		// X-rot (adjusts y)
		target = vec3{
			target.x,
			target.y*gp::cos(pixel.y) - target.z*gp::sin(pixel.y),
			target.y*gp::sin(pixel.y) + target.z*gp::cos(pixel.y)
		};

		vec3 render_target{_camera.position};
		for(int i = 1; i < passes; ++i) {
			render_point distance = sdf(render_target);

			if(distance.distance <  epsilon) {
				return materials[distance.material](render_target);
			}

			depth += distance.distance;

			if(depth >= projection_end) {
				break;
			}

			render_target = _camera.position+depth*target;
		}
		return sky_box(render_target);
	}
};