gplib/include/gp/math/rendering/renderer.hpp

#pragma once

#include "gp_config.hpp"

#include "gp/algorithms/min_of.hpp"
#include "gp/utils/allocators/buddy.hpp"
#include "gp/functional/function.hpp"
#include "gp/containers/indexed_array.hpp"
#include "gp/math.hpp"
#include "gp/math/rendering_math.hpp"

// TODO: Namespace this correctly
// BUG: The rendering behaves improperly, I don't know why

namespace gp {
	namespace math {
		namespace rendering {

			using vec2 = gp::math::vec2_g<>;
			using vec3 = gp::math::vec3_g<>;
			using vec4 = gp::math::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, -5}, {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::math::pi<g_t>,gp::math::pi<g_t>};

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

					vec3 render_target{_camera.position};
					for(int i = 0; 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);
				}
			};
		}
	}
}