如何正确检测 sdl2 中的按键按下和释放

Posted 2023-02-22

【中文标题】如何正确检测 sdl2 中的按键按下和释放

【英文标题】：How to correctly detect key press and release in sdl2

【发布时间】：2017-01-31 02:05:22

【问题描述】：

我的完整代码-

#include <SDL.h>
#include <SDL_opengl.h>
#include <GL\GLU.h>
#include <fstream>

using namespace std;


int index = 0;
int speed = 0;
int frames = 0;
int lasttime = 0;
int mousex = 0;
int mousey = 0;
bool postRedraw = true;

int screenWidth = 640;
int screenHeight = 480;
float screenAspect = screenWidth/screenHeight;

bool init();
bool initGL();
void handleKeys( unsigned char key, int x, int y );
void update();
void render();
void close();
void Initialize();
void handleEvents();


ofstream logFile;

SDL_Window* gWindow = NULL;
bool isRunning = true;
SDL_GLContext gContext;
float xpos = 0.0;
float ypos = 0.0;
float zpos = 0.0;


void Initialize()

    gluPerspective(60.0f, screenAspect, 1.0, 400.0);
    glEnable(GL_COLOR_MATERIAL);
    glEnable(GL_NORMALIZE);
    glTranslatef(0.0f, 0.0f, -5.0f);
    glFrontFace(GL_CCW);
    glEnable(GL_LIGHT0);



void render()

    glTranslatef(xpos, ypos, zpos);
    glClear(GL_COLOR_BUFFER_BIT | GL_DEPTH_BUFFER_BIT);
    glColor3f(1.0, 0.0, 0.0);
    glBegin(GL_TRIANGLES);
        glVertex3f(-1.0f,0.0f,-1.0f);
        glVertex3f(0.0f, 1.0f, -1.0f);
        glVertex3f(0.0f, 2.0f, -2.0f);
    glEnd();
    postRedraw = true;



void handleEvents()

    const Uint8* keystates = SDL_GetKeyboardState(NULL);
    if(keystates[SDL_GetScancodeFromKey(SDLK_w)])
    
        zpos += 0.01;
    
    if(keystates[SDL_GetScancodeFromKey(SDLK_s)])
    
        zpos -= 0.01;
     else 
    


bool init()

    bool success = true;
    if( SDL_Init( SDL_INIT_VIDEO ) < 0 )
    
        logFile<<"SDL could not initialize! SDL Error: "<<SDL_GetError()<<endl;
        success = false;
    
    else
    
        SDL_GL_SetAttribute( SDL_GL_CONTEXT_MAJOR_VERSION, 2 );
        SDL_GL_SetAttribute( SDL_GL_CONTEXT_MINOR_VERSION, 1 );
        gWindow = SDL_CreateWindow( "SDL Tutorial", SDL_WINDOWPOS_UNDEFINED, SDL_WINDOWPOS_UNDEFINED, screenWidth, screenHeight, SDL_WINDOW_OPENGL | SDL_WINDOW_RESIZABLE );
        if( gWindow == NULL )
        
            logFile<<"Window could not be created! SDL Error: "<<SDL_GetError()<<endl;
            success = false;
        
        else
        
            gContext = SDL_GL_CreateContext( gWindow );
            if( gContext == NULL )
            
                logFile<<"OpenGL context could not be created! SDL Error: "<<SDL_GetError()<<endl;
                success = false;
            
            else
            
                if( SDL_GL_SetSwapInterval( 1 ) < 0 )
                
                    logFile<<"Warning: Unable to set VSync! SDL Error: "<<SDL_GetError()<<endl;
                
                if( !initGL() )
                
                    logFile<<"Unable to initialize OpenGL!"<<endl;
                    success = false;
                
            
        
    
    logFile.open("log.txt");
    if(logFile.is_open())
    
        success = true;
     else 
        success = false;
    
    return success;


bool initGL()

    bool success = true;
    GLenum error = GL_NO_ERROR;
    glMatrixMode( GL_PROJECTION );
    glLoadIdentity();
    error = glGetError();
    if( error != GL_NO_ERROR )
    
        logFile<<"Error initializing OpenGL! "<<gluErrorString( error )<<endl;
        success = false;
    
    glMatrixMode( GL_MODELVIEW );
    glLoadIdentity();
    glEnable(GL_CULL_FACE);
    glEnable(GL_DEPTH_TEST);
    error = glGetError();
    if( error != GL_NO_ERROR )
    
        logFile<<"Error initializing OpenGL! "<<gluErrorString( error )<<endl;
        success = false;
    
    glClearColor( 0.f, 0.f, 0.f, 1.f );
    error = glGetError();
    if( error != GL_NO_ERROR )
    
        logFile<<"Error initializing OpenGL! "<<gluErrorString( error );
        success = false;
    

    return success;



void close()

    logFile.close();
    SDL_DestroyWindow( gWindow );
    gWindow = NULL;
    SDL_Quit();


int main( int argc, char* args[] )

    if( !init() )
    
        logFile<<"Failed to initialize!"<<endl;
    
    else
    

        SDL_Event event;
        Initialize();
        lasttime = SDL_GetTicks();
        while(isRunning)
        
            while( SDL_PollEvent( &event ) != 0 )
            
                if(event.type == SDL_QUIT)
                
                    isRunning = false;
                 else if(event.type == SDL_MOUSEMOTION) 
                    SDL_GetMouseState(&mousex, &mousey);
                 else if(event.type == SDL_MOUSEBUTTONDOWN) 
                    SDL_GetMouseState(&mousex, &mousey);
                 else if(event.type == SDL_MOUSEBUTTONUP) 
                    SDL_GetMouseState(&mousex, &mousey);
                
            
            handleEvents();
            if(postRedraw)
            
                postRedraw = false;
                render();
                SDL_GL_SwapWindow( gWindow );
            
            if((SDL_GetTicks()-lasttime)>=1000)
            
                lasttime = SDL_GetTicks();
                speed = frames;
                logFile<<speed<<endl;
                frames = 0;
             else 
                frames++;
            
        
    

    close();

    return 0;

以上代码仅用于测试，我有问题的简约代码是-

void handleEvents()

    const Uint8* keystates = SDL_GetKeyboardState(NULL);
    if(keystates[SDL_GetSancodeFromKey(SDLK_w)]) 
        zpos += 0.01;
    
    if(keystates[SDL_GetScancodeFromKey(SDLK_s)])
    
        zpos -= 0.01;
     else 
    

预期： 按下 w/s 键时，绘制的三角形将向前/向后移动。

输出： 即使松开按键，三角形也会继续向所需方向移动。

【问题讨论】：

建议放弃最后两个问题，因为它们不相关，并且使这个问题过于宽泛，更有可能被关闭。如果您真的对它们的答案感兴趣，请再问两个问题。

这是错字吗？ const Uint8* keystates = SDL_GetKeyboardState(NULL); 这里没有if，但是在更大的代码块中有一个if。

那是错误的，我更新了我的问题

【参考方案1】：

随着时间的推移，你会累积你的矩阵变化。 glTranslatef 通过平移修改 current 矩阵。下一帧它再次修改它。再一次，....

您应该使用glLoadIdentity() 调用重置矩阵。请注意，它会修改当前选定的矩阵，并将撤消您在Initialize 中所做的矩阵更改（至少在这里您的glTranslatef - 透视图应该转到GL_PROJECTION 矩阵，您还没有这样做）。