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//
// Created by Keuin on 2022/4/12.
//
#ifndef RT_VIEWPORT_H
#define RT_VIEWPORT_H
#include "timer.h"
#include "bitmap.h"
#include "ray.h"
#include "vec.h"
#include "hitlist.h"
#include <cstdlib>
#include <memory>
#include <limits>
#include <vector>
#include <iostream>
#include <cstdint>
#include <random>
// bias context, used for placing sub-pixels
class bias_ctx {
bool enabled; // put all together, eliminating a virtual function call
std::mt19937_64 mt;
std::uniform_real_distribution<double> uni{0.0, 1.0};
public:
bias_ctx() : enabled(false) {}
bias_ctx(uint64_t seed) : enabled(true), mt(std::mt19937_64{seed}) {}
void operator()(double &bx, double &by) {
if (enabled) {
bx = uni(mt);
by = uni(mt);
} else {
bx = 0.0;
by = 0.0;
}
}
};
template<typename T>
class viewport {
public:
virtual bitmap<T> render(const hitlist<T> &world, vec3d viewpoint, uint16_t image_width, uint16_t image_height) = 0;
virtual ~viewport() = default;
};
// Single sampled viewport which supports bias sampling
template<typename T>
class basic_viewport : public viewport<T> {
const double half_width, half_height; // viewport size
const vec3d center; // coordinate of the viewport center point
public:
basic_viewport() = delete;
basic_viewport(double width, double height, vec3d viewport_center) :
half_width(width / 2.0), half_height(height / 2.0), center(viewport_center) {}
virtual bitmap<T>
render(const hitlist<T> &world, vec3d viewpoint, uint16_t image_width, uint16_t image_height) override {
bias_ctx bc{};
static constexpr uint64_t default_diffuse_seed = 123456789012345678ULL;
return render(world, viewpoint, image_width, image_height, bc, default_diffuse_seed);
}
/**
* Generate the image seen on given viewpoint.
* @param bx bias on x axis (0.0 <= bx < 1.0)
* @param by bias on y axis (0.0 <= by < 1.0)
* @return
*/
virtual bitmap<T> render(const hitlist<T> &world, vec3d viewpoint,
uint16_t image_width, uint16_t image_height,
bias_ctx &bias, uint64_t diffuse_seed) const {
bitmap<T> image{image_width, image_height};
random_uv_gen_3d ruvg{diffuse_seed};
double bx, by;
const auto r = center - viewpoint;
const int img_hw = image_width / 2, img_hh = image_height / 2;
// iterate over every pixel on the image
for (int j = -img_hh + 1; j <= img_hh; ++j) { // axis y, transformation is needed
for (int i = -img_hw; i < img_hw; ++i) { // axis x
bias(bx, by); // get a random bias (bx, by) for sub-pixel sampling
assert(0 <= bx);
assert(0 <= by);
assert(bx < 1.0);
assert(by < 1.0);
const vec3d off{
.x=(1.0 * i + bx) / img_hw * half_width,
.y=(1.0 * j + by) / img_hh * half_height,
.z=0.0
}; // offset on screen plane
const auto dir = r + off; // direction vector from camera to current pixel on screen
ray3d ray{viewpoint, dir}; // from camera to pixel (on the viewport)
const auto pixel = world.color(ray, ruvg);
image.set(i + img_hw, -j + img_hh, pixel);
}
}
return image;
}
};
#endif //RT_VIEWPORT_H
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