我正在尝试使用xcode作为编译器和SFML作为库在C ++中制作一个简单的游戏。到目前为止，我已经创建了一个GUI，一个背景和一个精灵（用于宇宙飞船）。我还添加了箭头键检测以便能够移动对象，但问题是当我移动对象时它不能平滑移动，你可以看到它有点“跳跃”。
#include <SFML/Audio.hpp>
#include <SFML/Graphics.hpp>
#include "Spaceship.hpp"
#include <vector>
// Here is a small helper for you! Have a look.
#include "ResourcePath.hpp"
int main(int, char const**)
{
// Create the main window
sf::RenderWindow window(sf::VideoMode(800, 600), "SpaceShuttle");
window.setFramerateLimit(30);
// Call to non-static member function without an object argument
// Set the Icon
sf::Image icon;
if (!icon.loadFromFile(resourcePath() + "space-shuttle.png")) {
return EXIT_FAILURE;
}
window.setIcon(icon.getSize().x, icon.getSize().y, icon.getPixelsPtr());
// Load a sprite to display
sf::Texture texture;
if (!texture.loadFromFile(resourcePath() + "bg.png")) {
return EXIT_FAILURE;
}
sf::Sprite sprite(texture);
// Create a graphical text to display
sf::Font font;
if (!font.loadFromFile(resourcePath() + "sansation.ttf")) {
return EXIT_FAILURE;
}
sf::Text text("SpaceShuttle K1LLM33K", font, 50);
text.setFillColor(sf::Color::White);
text.setPosition(100.0, 130.0);
// Load a music to play
/* sf::Music music; if (!music.openFromFile(resourcePath() + "nice_music.ogg")) { return EXIT_FAILURE; }
// Play the music
music.play();
*/
Spaceship spaceship(window);
sf::Clock sf_clock;
// Start the game loop
while (window.isOpen()) {
// Process events
sf::Event event;
while (window.pollEvent(event)) {
// Close window: exit
if (event.type == sf::Event::Closed) {
window.close();
}
// Escape pressed: exit
if (event.type == sf::Event::KeyPressed && event.key.code == sf::Keyboard::Escape) {
window.close();
}
// Move Spaceship
if(sf::Keyboard::isKeyPressed(sf::Keyboard::Left)) { spaceship.moveship('l'); }
else if(sf::Keyboard::isKeyPressed(sf::Keyboard::Right)) { spaceship.moveship('r'); }
else if(sf::Keyboard::isKeyPressed(sf::Keyboard::Up)) { spaceship.moveship('u'); }
else if(sf::Keyboard::isKeyPressed(sf::Keyboard::Down)) { spaceship.moveship('d'); }
}
// Clear screen
window.clear();
// Draw the sprite(s)
window.draw(sprite);
spaceship.drawsprite(window);
// Draw the string(s)
window.draw(text);
// Update the window
window.display();
}
return EXIT_SUCCESS;
}
#include <SFML/Audio.hpp>
#include <SFML/Graphics.hpp>
#include "ResourcePath.hpp"
#include "Spaceship.hpp"
Spaceship::Spaceship(sf::RenderWindow& game_window){
auto surface = game_window.getSize();
ss_x = surface.x/2;
ss_y = surface.y/2;
ss_speed = 5;
ss_width = 128;
ss_height = 128;
ss_radius = ss_width/2;
}
void Spaceship::drawsprite(sf::RenderWindow& game_window){
sf::Texture ship;
if (!ship.loadFromFile(resourcePath() + "space-shuttle-64.png")) {
return EXIT_FAILURE;
}
sf::Sprite ss_sprite(ship);
ss_sprite.setPosition(ss_x - ss_sprite.getGlobalBounds().width/2, ss_y - ss_sprite.getGlobalBounds().height/2);
game_window.draw(ss_sprite);
}
void Spaceship::moveship(char move){
if(move == 'l'){ ss_x -= ss_speed; }
else if(move == 'r'){ ss_x += ss_speed; }
else if(move == 'u'){ ss_y -= ss_speed; }
else if(move == 'd'){ ss_y += ss_speed; }
}
Spaceship::~Spaceship(){}
#ifndef Spaceship_hpp
#define Spaceship_hpp
#include <iostream>
#include <SFML/Audio.hpp>
#include <SFML/Graphics.hpp>
#include <stdio.h>
using namespace std;
class Spaceship {
public:
Spaceship();
Spaceship(sf::RenderWindow&);
~Spaceship();
void moveship(char);
void drawsprite(sf::RenderWindow&);
private:
signed int ss_x, ss_y;
unsigned int ss_speed;
int ss_width, ss_height, ss_radius;
};
#endif /* Spaceship_hpp */
答案 0 :(得分：1)
正如评论中所建议的那样，问题在于您没有考虑计算中两帧之间的经过时间。因此，所发生的是你在任何一帧都增加了固定的速度，忽略了两个连续帧可能需要一个非常不同的时间才能完成的事实。
还有另一个问题（似乎是您问题的主要来源）：您正在检查按键是否在事件循环中。这是不正确的，只有按下您的键并且在循环期间还有其他事件时才会出现这种情况。你需要在每一帧检查这一点。
解决上一个问题的另一种方法是，当您为所需的键检测到true / false时，将布尔标记设置为press / release去测试。如果您查看isKeyPressed方法，您还会发现第二种方法比第一种方法更有效。
更改主循环以获取每帧的经过时间的最简单方法according to the docs是这样的：
sf::Clock sf_clock;
// Start the game loop
while (window.isOpen()) {
// Get time elapsed since last frame
float dt = clock.restart().asSeconds();
// Process events
sf::Event event;
while (window.pollEvent(event)) {
// Close window: exit
}
// Move Spaceship, this must be done outside of the pollEvent loop !
if(sf::Keyboard::isKeyPressed(sf::Keyboard::Left)) spaceship.moveship(dt, 'l');
else if(sf::Keyboard::isKeyPressed(sf::Keyboard::Right)) spaceship.moveship(dt, 'r');
if(sf::Keyboard::isKeyPressed(sf::Keyboard::Up)) spaceship.moveship(dt, 'u');
else if(sf::Keyboard::isKeyPressed(sf::Keyboard::Down)) spaceship.moveship(dt, 'd');
}
// Draw, etc..
}
然后你必须在dt方法中考虑moveship（我在if / else if中更改了switch case，在这种情况下我觉得更干净，应该更有效率）：
void Spaceship::moveship(float dt, char move) {
switch (move) {
case 'l': ss_x -= dt * ss_speed_x; break;
case 'r': ss_x += dt * ss_speed_x; break;
case 'u': ss_y -= dt * ss_speed_y; break;
case 'd': ss_y += dt * ss_speed_y; break;
}
}
根据Jesper Juhl的建议，我在这里做了一些integration（你应该看看the article）。
顺便说一下，我建议您对代码进行一些修改：// First of all, you should use floating-point values that you convert
// in screen space at render time for your coordinates
// You could also think about using vectors instead, I won't here
class Spaceship {
private:
float ss_x, ss_y;
float ss_speed_x, ss_speed_y;
// You should also store your sprite instead of creating it over
// and over again
sf::Sprite ss_sprite;
};
Spaceship::Spaceship(sf::RenderWindow& game_window) {
// You can then take those modifications into account
// in your constructor:
auto surface = game_window.getSize();
ss_x = ss_y = 0.5f;
ss_speed_x = 5.f / surface.x;
ss_speed_y = 5.f / surface.y;
ss_width = 128;
ss_height = 128;
ss_radius = ss_width/2;
sf::Texture ship;
if (!ship.loadFromFile(resourcePath() + "space-shuttle-64.png")) {
// This is really an awful way to handle an error, but I won't
// go into details here. A better way would be to have an Init()
// method that returns an error code on failure for example.
exit(EXIT_FAILURE);
}
ss_sprite = sf::Sprite(ship);
// http://www.sfml-dev.org/documentation/2.4.1/classsf_1_1Transformable.php#a56c67bd80aae8418d13fb96c034d25ec
ss_sprite.setOrigin(ss_width / 2, ss_height / 2);
}
// Finally, you reflect those modifications in your draw code
void Spaceship::drawsprite(sf::RenderWindow& game_window){
auto size = game_window.getSize();
ss_sprite.setPosition(ss_x * size.x, ss_y * size.y);
game_window.draw(ss_sprite);
}