c – 如何使用此代码设置重力？
作者：互联网
我正在尝试制作一个游戏并且在重力上停留…..在下面的代码中,一个矩形代表一个玩家,当我按下键时它会在y轴上移动但是当我激活重力时(即重置它)它没有动画(即它没有跳跃)而是只停留在它的位置.我正在使用C的SFML库,这是一个游戏开发工具.请帮忙！
#include <SFML/Graphics.hpp>
int main(){
sf::RenderWindow window(sf::VideoMode(800, 600, 32), "Gravity");
sf::RectangleShape rectangle;
rectangle.setSize(sf::Vector2f(100, 100));
rectangle.setFillColor(sf::Color::Black);
rectangle.setPosition(sf::Vector2f(10, 350));
while(window.isOpen())
{
sf::Event Event;
while(window.pollEvent(Event))
{
if(Event.type == sf::Event::Closed)
{
window.close();
}
}
if(sf::Keyboard::isKeyPressed(sf::Keyboard::Up))
{
rectangle.move(0, -1);
}
if(rectangle.getPosition().y >= 350-1)
{
rectangle.setPosition(0, 350);
}
window.display();
window.clear(sf::Color::Cyan);
window.draw(rectangle);
}
}
解决方法:
从理论上讲,你的代码可以工作,但是有一个重要的问题：
>你的初始职位是350.
>现在你的“跳跃代码”(允许玩家无限期飞行！)触发器,你的位置变为349.
>但是,保持玩家不从屏幕上掉落的代码(y> = 350-1)基本上解析为支票y> = 349,这将是真的,因此您的位置将永久重置为350.
要解决此问题,只需删除-1或用>替换> =运算符即可.
虽然您的方法应该有效(一旦应用上述修复),您应该重新考虑您的策略并存储除位置之外的速度.我最近编写了以下示例代码.它远非完美,但它应该教你一些跳跃和跑步游戏的基础知识(不一定是做这些事情的唯一方法)：
>允许玩家跳跃.
>施加重力.
>允许玩家根据他按下一个键的时间来确定跳跃高度.
#include <SFML/Graphics.hpp>
int main(int argc, char **argv) {
sf::RenderWindow window;
sf::Event event;
sf::RectangleShape box(sf::Vector2f(32, 32));
box.setFillColor(sf::Color::White);
box.setOrigin(16, 32);
box.setPosition(320, 240);
window.create(sf::VideoMode(640, 480), "Jumping Box [cursor keys + space]");
window.setFramerateLimit(60);
window.setVerticalSyncEnabled(false);
// player position
sf::Vector2f pos(320, 240);
// player velocity (per frame)
sf::Vector2f vel(0, 0);
// gravity (per frame)
sf::Vector2f gravity(0, .5f);
// max fall velocity
const float maxfall = 5;
// run acceleration
const float runacc = .25f;
// max run velocity
const float maxrun = 2.5f;
// jump acceleration
const float jumpacc = -1;
// number of frames to accelerate in
const unsigned char jumpframes = 10;
// counts the number of frames where you can still accelerate
unsigned char jumpcounter = 0;
// inputs
bool left = false;
bool right = false;
bool jump = false;
while (window.isOpen()) {
while (window.pollEvent(event)) {
switch(event.type) {
case sf::Event::KeyPressed:
case sf::Event::KeyReleased:
switch (event.key.code) {
case sf::Keyboard::Escape:
window.close();
break;
case sf::Keyboard::Left:
left = event.type == sf::Event::KeyPressed;
break;
case sf::Keyboard::Right:
right = event.type == sf::Event::KeyPressed;
break;
case sf::Keyboard::Space:
jump = event.type == sf::Event::KeyPressed;
break;
}
break;
case sf::Event::Closed:
window.close();
break;
}
}
// logic update start
// first, apply velocities
pos += vel;
// determine whether the player is on the ground
const bool onground = pos.y >= 480;
// now update the velocity by...
// ...updating gravity
vel += gravity;
// ...capping gravity
if (vel.y > maxfall)
vel.y = maxfall;
if (left) { // running to the left
vel.x -= runacc;
}
else if (right) { // running to the right
vel.x += runacc;
}
else { // not running anymore; slowing down each frame
vel.x *= 0.9;
}
// jumping
if (jump) {
if (onground) { // on the ground
vel.y += jumpacc * 2;
jumpcounter = jumpframes;
}
else if (jumpcounter > 0) { // first few frames in the air
vel.y += jumpacc;
jumpcounter--;
}
}
else { // jump key released, stop acceleration
jumpcounter = 0;
}
// check for collision with the ground
if (pos.y > 480) {
vel.y = 0;
pos.y = 480;
}
// check for collision with the left border
if (pos.x < 16) {
vel.x = 0;
pos.x = 16;
}
else if (pos.x > 624) {
vel.x = 0;
pos.x = 624;
}
// logic update end
// update the position
box.setPosition(pos);
window.clear();
window.draw(box);
window.display();
}
return 0;
}