所以基本上这是我正在制作的一个小程序，它模拟一个具有给定质量的物体从选定的高度坠落。它应该以与下降时间相匹配的速度落下窗户。
我一直在绞尽脑汁，我无法让它与任何其他 drop_ht {100} 和 obj_mass {1.0} 一起正常工作。
我认为我通过将屏幕除以下降高度来获得“每米像素”是在正确的轨道上，但是每当我增加 drop_ht 下降速度增加。
例如：drop_ht = 100 和 obj_mass = 1 fall_time 为 16.1 秒。目前该物体确实需要 16.1 秒才能落下窗户。但是，如果我将 drop_ht 加倍到 200，那么下降也只需要大约 8 秒。
附言。我知道其中一些计算没有与其他东西一起完全优化，但这仍在进行中！ :)
这是主文件：
#include <SFML/Graphics.hpp>
#include <SFML/Window/Event.hpp>
#include <iostream>
#include <string>
#include <vector>
#include "inputs.h"
#include "ball_drop.h"
#include "calculations.h"
int main()
{
double x_res{ 1000.f };
double y_res{ 800.f };
sf::RenderWindow window(sf::VideoMode(x_res, y_res), "Freefall Calculator");
window.setFramerateLimit(60);
double x_middle{ x_res / 2.0 };
double y_midlle{ y_res / 2.0 };
/*------------------------------------*/
/* Create text to display on screen */
/*------------------------------------*/
sf::Font arial;
if (!arial.loadFromFile("fonts\\arial.ttf"))
{
std::cout << "Cannot load font file.";
}
sf::Text menu_text;
menu_text.setFont(arial);
//menu_text.setFillColor(sf::Color::Black);
menu_text.setOutlineThickness(0.5);
std::vector <std::string> welcome_text;
welcome_text.push_back("Welcome to Freefall Calculator!");
welcome_text.push_back("Please choose the object you would like to drop....");
std::vector <std::string> obj_selection_txt;
obj_selection_txt.push_back("Cube selected!");
obj_selection_txt.push_back("Ball selected!");
int welcome_vec_size = welcome_text.size()-1;
/* Used to iterate through different pages of the application */
int next_display{ 0 };
/* Text for object selection */
sf::Vector2f cube_text_pos(230.0, 500.0);
sf::Vector2f ball_text_pos(640.0, 500.0);
sf::Text object_text;
object_text.setFont(arial);
//object_text.setFillColor(sf::Color::Black);
object_text.setString("Cube");
object_text.setPosition(cube_text_pos);
/* Text for pressing space bar */
sf::Text press_space;
press_space.setFont(arial);
//press_space.setFillColor(sf::Color::Black);
press_space.setString("Push space to continue...");
press_space.setPosition(320, 700);
/* User input text */
sf::Text user_text;
user_text.setFont(arial);
sf::String user_input;
/* User input page */
int next_text_input{ 0 }; // changes input selection
sf::Text get_drop_ht;
get_drop_ht.setFont(arial);
//get_drop_ht.setFillColor(sf::Color::Black);
get_drop_ht.setPosition(0, 0);
get_drop_ht.setString("Enter drop height (Meters):");
sf::Text input_drop_ht;
input_drop_ht.setFont(arial);
input_drop_ht.setPosition(400, 0);
input_drop_ht.setString("I");
std::string drop_ht_string;
sf::Text get_obj_mass;
get_obj_mass.setFont(arial);
//get_obj_mass.setFillColor(sf::Color::Black);
get_obj_mass.setPosition(0, 300);
get_obj_mass.setString("Enter object mass (KG):");
sf::Text input_obj_mass;
input_obj_mass.setFont(arial);
input_obj_mass.setPosition(400, 300);
std::string obj_mass_string;
/*----------------------------------*/
/* Load in textures for objects */
/*----------------------------------*/
sf::ContextSettings settings;
settings.antialiasingLevel = 8;
sf::Texture concrete;
if (!concrete.loadFromFile("textures\\concrete_texture.jpg"))
{
std::cout << "Cannot load concrete texture\n";
}
sf::Texture crate;
if (!crate.loadFromFile("textures\\crate_texture.jpg"))
{
std::cout << "Cannot load crate texture\n";
}
sf::Texture backgorund_texture;
if (!backgorund_texture.loadFromFile("textures\\sky_bg.png"))
{
std::cout << "Cannot load background texture\n";
}
sf::Texture cloud_texture;
if (!cloud_texture.loadFromFile("textures\\cloud.png"))
{
std::cout << "Cannot load clout texture\n";
}
/*----------------------*/
/* Create menu objects */
/*----------------------*/
sf::CircleShape menu_ball;
menu_ball.setRadius(75);
sf::Vector2f menu_ball_pos(600, 300);
menu_ball.setPosition(menu_ball_pos);
menu_ball.setOutlineColor(sf::Color::White);
menu_ball.setOutlineThickness(0.0);
menu_ball.setTexture(&concrete);
sf::Vector2f ff_ball_pos(x_middle, 0);
sf::RectangleShape menu_cube;
menu_cube.setSize(sf::Vector2f(150.f, 150.f));
sf::Vector2f menu_cube_pos(200, 300);
menu_cube.setPosition(menu_cube_pos);
menu_cube.setOutlineColor(sf::Color::White);
menu_cube.setOutlineThickness(10.0);
menu_cube.setTexture(&crate);
sf::Vector2f ff_cube_pos(x_middle, 0);
std::vector <float> cube_size(60.f, 60.f);
float ball_rad{ 30.f };
/*-------------------------*/
/* Creates menu background */
/*-------------------------*/
sf::Sprite background_image;
background_image.setScale(1,1);
background_image.setTexture(backgorund_texture);
//background_image.setColor(sf::Color::Blue);
sf::Sprite cloud;
cloud.setTexture(cloud_texture);
cloud.setScale(0.1, 0.1);
/*---------------------*/
/* Main Objects */
/*---------------------*/
int object_chosen {0};
double drop_ht {}; // drop ht for maths
double obj_mass{}; // object mass for maths
double fall_velocity{};
double rel_screen_drop_ht{};
double fall_time{};
const float time_delta{ 0.1 };
/*--------------------*/
/* Time Objects */
/*---------------------*/
sf::Clock mass_input_clock;
bool obj_mass_input_clock_start{ false };
sf::Clock text_cursor_clock;
bool text_cursor_clock_start{ false };
int switch_text_cursor_colour{ 0 };
sf::Clock freefall_clock;
bool freefall_clock_start{ false };
/*---------------------*/
/* main event loop */
/*---------------------*/
while (window.isOpen())
{
sf::Event event;
while (window.pollEvent(event))
{
if (event.type == sf::Event::Closed)
{
window.close();
}
if (sf::Keyboard::isKeyPressed(sf::Keyboard::Escape))
{
window.close();
}
if (event.type == sf::Event::KeyPressed)
{
if (event.key.code == sf::Keyboard::Space)
{
/* This changes to the object selection menu */
if (next_display < 1)
{
next_display = 1;
}
/* Cube chosen */
else if (object_chosen == 0 && next_display == 1)
{
menu_text.setString(obj_selection_txt[0]);
menu_text.setCharacterSize(75);
menu_cube.setOutlineThickness(0);
next_display = 2;
}
/* Ball Chosen */
else if (object_chosen == 1 && next_display == 1)
{
menu_text.setString(obj_selection_txt[1]);
menu_text.setCharacterSize(75);
menu_ball.setOutlineThickness(0);
next_display = 2;
}
/* Goes to next text input when drop_ht string length is > 0 */
else if ((next_display == 3) && (drop_ht_string.length() > 0) && (next_text_input == 0))
{
next_text_input = 1;
input_drop_ht.setFillColor(sf::Color::Green);
input_obj_mass.setString("I");
text_cursor_clock_start = true;
}
else if ((next_text_input == 1) && (obj_mass_string.length() > 0))
{
mass_input_clock.restart();
input_obj_mass.setFillColor(sf::Color::Green);
obj_mass_input_clock_start = true;
menu_ball.setPosition(ff_ball_pos);
menu_cube.setPosition(ff_cube_pos);
menu_ball.setRadius(ball_rad);
menu_cube.setSize(sf::Vector2f::Vector2(cube_size[0], cube_size[1]));
//debug use of calculation functions
fall_time = calculate_free_fall_time(obj_mass, drop_ht);
//calculate_distance_fallen(drop_ht, fall_time);
fall_velocity = obj_fall_velocity(fall_time, drop_ht, y_res);
std::cout << "fall velocity = " << fall_velocity << std::endl;
std::cout << "drop height = " << drop_ht << std::endl;
std::cout << "fall time = " << fall_time << std::endl;
}
}
/* Alows user to backaspace to delete text inputs */
if (event.key.code == sf::Keyboard::BackSpace)
{
if (next_text_input == 0)
{
input_drop_ht.setString(erase_text(drop_ht_string));
}
else if (next_text_input == 1)
{
input_obj_mass.setString(erase_text(obj_mass_string));
}
}
if (event.key.code == sf::Keyboard::Right)
{
if (next_display == 1)
{
menu_ball.setOutlineThickness(10.0);
menu_cube.setOutlineThickness(0.0);
object_text.setString("Ball");
object_text.setPosition(ball_text_pos);
object_chosen = 1;
std::cout << "ball chosen\n";
}
}
if (event.key.code == sf::Keyboard::Left)
{
if (next_display == 1)
{
menu_ball.setOutlineThickness(0.0);
menu_cube.setOutlineThickness(10.0);
object_text.setString("Cube");
object_text.setPosition(cube_text_pos);
object_chosen = 0;
std::cout << "cube chosen\n";
}
}
}
if ((event.type == sf::Event::TextEntered) && (next_display == 3))
{
if (next_text_input == 0)
{
if (event.text.unicode >= 48 && event.text.unicode <= 57)
{
//std::cout << "ASCII character typed: " << static_cast<char>(event.text.unicode) << std::endl;
text_cursor_clock_start = false;
input_drop_ht.setFillColor(sf::Color::White);
drop_ht_string += event.text.unicode;
input_drop_ht.setString(drop_ht_string);
drop_ht = std::stod(drop_ht_string);
}
}
else if (next_text_input == 1)
{
if (event.text.unicode >= 48 && event.text.unicode <= 57)
{
//std::cout << "ASCII character typed: " << static_cast<char>(event.text.unicode) << std::endl;
text_cursor_clock_start = false;
input_obj_mass.setFillColor(sf::Color::White);
obj_mass_string += event.text.unicode;
input_obj_mass.setString(obj_mass_string);
obj_mass = std::stod(obj_mass_string);
}
}
}
}
/*************************************/
/****** Display specific events ******/
/*************************************/
/* Changes the font size and text position for menu text */
if (next_display == 0)
{
menu_text.setPosition(165, 300);
menu_text.setCharacterSize(50);
menu_text.setString(welcome_text[0]);
}
else if (next_display == 1)
{
menu_text.setPosition(165, 0);
menu_text.setCharacterSize(30);
menu_text.setString(welcome_text[1]);
}
/* Changes the y pos of object when it has been selected to make
it drop from the screen */
else if (next_display == 2)
{
float menu_drop_velocity{ 10 };
menu_text.setPosition(250, 0);
menu_cube_pos.y += menu_drop_velocity;
menu_ball_pos.y += menu_drop_velocity;
menu_cube.setPosition(menu_cube_pos);
menu_ball.setPosition(menu_ball_pos);
//std::cout << menu_ball_pos.y << std::endl;
if ((menu_ball_pos.y > y_res) || (menu_cube_pos.y > y_res))
{
next_display = 3;
text_cursor_clock_start = true;
}
}
else if (next_display == 3)
{
/*************************/
/****** Time Events ******/
/*************************/
// This handles the delay when the object mass has been inputted to //
// allow the text enough time to go green before changing to the //
// object drop animation. //
if (obj_mass_input_clock_start)
{
sf::Time obj_seconds_passed = mass_input_clock.getElapsedTime();
sf::Time obj_seconds = sf::seconds(1.f);
if (obj_seconds_passed > obj_seconds)
{
/*menu_ball.setPosition(ff_ball_pos);
menu_cube.setPosition(ff_cube_pos);
menu_ball.setRadius(10.f);
menu_cube.setSize(sf::Vector2f::Vector2(10.f, 10.f));*/
//freefall_clock.restart();
next_display = 4;
freefall_clock_start = true;
freefall_clock.restart();
}
}
// This handles the text cursor pulsating from white to black. Pulse //
// frequency can be changed by editted "text_cursor_pulse_seconds" //
if (text_cursor_clock_start)
{
sf::Time cursor_time_passed = text_cursor_clock.getElapsedTime();
sf::Time text_cursor_pulse_seconds = sf::seconds(0.5f);
if ((cursor_time_passed > text_cursor_pulse_seconds) && (switch_text_cursor_colour == 0))
{
switch_text_cursor_colour = 1;
if (next_text_input == 0)
{
input_drop_ht.setFillColor(sf::Color::Black);
}
else if (next_text_input == 1)
{
input_obj_mass.setFillColor(sf::Color::Black);
}
text_cursor_clock.restart();
}
else if ((cursor_time_passed > text_cursor_pulse_seconds) && (switch_text_cursor_colour == 1))
{
switch_text_cursor_colour = 0;
if (next_text_input == 0)
{
input_drop_ht.setFillColor(sf::Color::White);
}
else if (next_text_input == 1)
{
input_obj_mass.setFillColor(sf::Color::White);
}
text_cursor_clock.restart();
}
//std::cout << cursor_time_passed.asSeconds() << std::endl;
//std::cout << "switch colour: " << switch_text_cursor_colour << std::endl;
}
}
else if (next_display == 4)
{
if (freefall_clock_start == true)
{
sf::Time ff_timer = freefall_clock.getElapsedTime();
std::cout << ff_timer.asSeconds() << std::endl; // debug
ff_cube_pos.y += fall_velocity;
ff_ball_pos.y += fall_velocity;
menu_cube.setPosition(ff_cube_pos);
menu_ball.setPosition(ff_ball_pos);
if ((ff_ball_pos.y == (y_res - (ball_rad *2))) || (ff_cube_pos.y > (y_res - cube_size[0])))
{
freefall_clock_start = false;
//freefall_clock.restart();
}
}
}
/*******************************/
/*---------------------*/
/* Main draw block */
/*---------------------*/
window.clear();
//window.draw(background_image);
/* Application welcoms page */
if (next_display == 0)
{
//window.draw(cloud);
window.draw(menu_text);
window.draw(press_space);
}
// Object selection page
else if (next_display == 1)
{
window.draw(menu_text);
window.draw(menu_ball);
window.draw(menu_cube);
window.draw(object_text);
window.draw(press_space);
}
/* Object selected page */
else if (next_display == 2)
{
window.draw(menu_text);
if (object_chosen == 0)
{
window.draw(menu_cube);
}
else
{
window.draw(menu_ball);
}
}
/* User input page */
else if (next_display == 3)
{
window.draw(press_space);
window.draw(get_drop_ht);
window.draw(get_obj_mass);
window.draw(input_drop_ht);
window.draw(input_obj_mass);
//window.draw(text_cursor);
}
else if (next_display == 4)
{
//window.draw(background_image);
//window.draw(cloud);
if (object_chosen == 0)
{
window.draw(menu_cube);
}
else if (object_chosen == 1)
{
window.draw(menu_ball);
}
}
window.display();
/* debug cout */
//std::cout << "next text: " << next_text << std::endl;
//std::cout << drop_ht << std::endl;
//std::cout << obj_mass << std::endl;
}
return 0;
}
这是完成计算的文件：
#include <iostream>
#include <SFML/Graphics.hpp>
#include <SFML/Window/Event.hpp>
#include <cmath>
#include <iomanip>
#include <vector>
#include "calculations.h"
const double g{ 9.80665 }; // Gravity (m/s2)
const double p{ 1.2041 }; // Density of air (kg/m3)
const double e{ 2.71828 }; // Euler's number (e)
const double k{ 0.24 }; // Air resistance (kg/m)
const double pi{ 3.142 }; // Pi
// Calculate free fall time
double calculate_free_fall_time(double mass, double height)
{
double freefall_time{ (sqrt(mass / (g * k))) * (acosh(pow(e,(height * k) / mass))) };
return freefall_time;
}
// Calculate object fall velocity on screen
double obj_fall_velocity(double fall_time, double drop_ht, double screen_ht)
{
double pix_per_meter = drop_ht / screen_ht;
return (drop_ht / fall_time) * pix_per_meter;
}
问题出在“obj_fall_velocity”函数上。我尝试了多种将屏幕高度除以下降高度以获得每米像素的方法。
// Calculate object fall velocity on screen
double obj_fall_velocity(double fall_time, double drop_ht, double screen_ht)
{
double pix_per_meter = drop_ht / screen_ht;
return (drop_ht / fall_time) * pix_per_meter;
}
目前，如果此函数的输入是 (16.1, 100, 800)，则对象会在 16 秒内落下屏幕，但如果输入是 (31.2, 200, 800)，则它会在大约 8 秒内落下屏幕。
我只是不明白......我可能已经盯着这个看太久了。