vectozavr-shooter/engine/Camera.cpp

//
// Created by Иван Ильин on 14.01.2021.
//

#include "Camera.h"
#include "utils/Log.h"
#include <cmath>

std::vector<Triangle> &Camera::project(std::shared_ptr<Mesh> mesh) {

    if(!_ready) {
        Log::log("Camera::project(): cannot project _tris without camera initialization ( Camera::init() ) ");
        return this->_triangles;
    }

    if(!mesh->isVisible())
        return this->_triangles;

    // Model transform matrix: translate _tris in the origin of body.
    Matrix4x4 M = Matrix4x4::Translation(mesh->position());
    Matrix4x4 VM = _V * M;

    // We don't want to waste time re-allocating memory every time
    std::vector<Triangle> clippedTriangles, tempBuffer;
    for(auto& t : mesh->triangles()) {

        double dot = t.norm().dot((mesh->position() + t[0] - _position).normalized());

        if(dot > 0)
            continue;

        Triangle clipped[2];
        // It needs to be cleared because it's reused through iterations. Usually it doesn't free memory.
        clippedTriangles.clear();

        // In the beginning we need to to translate drawTriangle from world coordinate to our camera system:
        // After that we apply clipping for all planes from _clipPlanes
        clippedTriangles.emplace_back(t * VM);
        for(auto& plane : _clipPlanes)
        {
            while(!clippedTriangles.empty())
            {
                clipped[0] = clippedTriangles.back();
                clipped[1] = clipped[0];
                clippedTriangles.pop_back();
                int additional = plane.clip(clipped[0], clipped[1]);

                for(int i = 0; i < additional; i++)
                    tempBuffer.emplace_back(clipped[i]);
            }
            clippedTriangles.swap(tempBuffer);
        }

        for(auto& clippedTriangle : clippedTriangles) {
            sf::Color color = clippedTriangle.color();
            sf::Color ambientColor = sf::Color(color.r * (0.3 * std::abs(dot) + 0.7),
                                               color.g * (0.3 * std::abs(dot) + 0.7),
                                               color.b * (0.3 * std::abs(dot) + 0.7),
                                               color.a);

            // Finally its time to project our clipped colored drawTriangle from 3D -> 2D
            // and transform it's coordinate to screen space (in pixels):
            clippedTriangle = clippedTriangle * _SP;

            clippedTriangle = Triangle(clippedTriangle[0] / clippedTriangle[0].w(),
                                       clippedTriangle[1] / clippedTriangle[1].w(),
                                       clippedTriangle[2] / clippedTriangle[2].w(),
                                       ambientColor);

            _triangles.emplace_back(clippedTriangle);
        }
    }

    return this->_triangles;
}

void Camera::init(int width, int height, double fov, double ZNear, double ZFar) {
    // We need to init camera only after creation or changing width, height, fov, ZNear or ZFar.
    // Because here we calculate matrix that does not change during the motion of _objects or camera
    _aspect = (double)width / (double)height;
    _P = Matrix4x4::Projection(fov, _aspect, ZNear, ZFar);
    _S = Matrix4x4::ScreenSpace(width, height);

    _SP = _S * _P; // screen-space-projections matrix

    // This is planes for clipping _tris.
    // Motivation: we are not interest in _tris that we cannot see.
    _clipPlanes.emplace_back(Plane(Point4D{0, 0, 1}, Point4D{0, 0, ZNear})); // near plane
    _clipPlanes.emplace_back(Plane(Point4D{0, 0, -1}, Point4D{0, 0, ZFar})); // far plane

    double thetta1 = M_PI*fov*0.5/180.0;
    double thetta2 = atan(_aspect * tan(thetta1));
    _clipPlanes.emplace_back(Plane(Point4D{-cos(thetta2), 0, sin(thetta2)}, Point4D{0, 0, 0})); // left plane
    _clipPlanes.emplace_back(Plane(Point4D{cos(thetta2), 0, sin(thetta2)}, Point4D{0, 0, 0})); // right plane
    _clipPlanes.emplace_back(Plane(Point4D{0, cos(thetta1), sin(thetta1)}, Point4D{0, 0, 0})); // down plane
    _clipPlanes.emplace_back(Plane(Point4D{0, -cos(thetta1), sin(thetta1)}, Point4D{0, 0, 0})); // up plane

    _ready = true;
    Log::log("Camera::init(): camera successfully initialized.");
}

std::vector<Triangle> &Camera::sorted() {

    // Sort _tris from back to front
    // This is some replacement for Z-buffer
    std::sort(_triangles.begin(), _triangles.end(), [](Triangle &t1, Triangle &t2)
    {
        std::vector<double> v_z1({t1[0].z(), t1[1].z(), t1[2].z()});
        std::vector<double> v_z2({t2[0].z(), t2[1].z(), t2[2].z()});

        std::sort(v_z1.begin(), v_z1.end());
        std::sort(v_z2.begin(), v_z2.end());

        double z1 = v_z1[0] + v_z1[1] + v_z1[2];
        double z2 = v_z2[0] + v_z2[1] + v_z2[2];

        return z1 > z2;
    });

    return _triangles;
}

void Camera::clear() {
    // Cleaning all _tris and recalculation of View matrix
    // That is like preparation for new camera shot: we need to set
    // the position of camera and insert new cartridge for photo.
    _triangles.clear();
    _V = Matrix4x4::View(_left, _up, _lookAt, _position);
}