SDL_GetKeyboardState(NULL) isn't working as expected - c++

Question

I am making a pong clone in C++/SDL2. To take keyboard input from multiple keys, I would like to use SDL_GetKeyboardState(NULL) with a Uint8. However, it isn't working as expected.
Expected behavior: pong paddles move up and down with each keypress.
Actual behavior: keys are not registered.
Here is my code (note that variables written in uppercase letters are from variables.h):
// g++ main.cpp `pkg-config sdl2 SDL2_ttf --cflags --libs`
#include <SDL2/SDL.h>
#include <SDL2/SDL_ttf.h>
#include <iostream> // For io
#include <time.h> // Rand seeder
const bool debug = true;
// Basic stuff needed for SDL2
const int WINDOW_WIDTH = 800;
const int WINDOW_HEIGHT = 600;
const int WINDOW_CENTER_X = WINDOW_WIDTH / 2;
const int WINDOW_CENTER_Y = WINDOW_HEIGHT / 2;
const char* WINDOW_TITLE = "Pong";
// Define the location of the paddles in the bitmap
const int PADDLE_BITMAP_X = 0;
const int PADDLE_BITMAP_Y = 0;
const int BALL_BITMAP_X = 100;
const int BALL_BITMAP_Y = 0;
// Positions of player 1 and player 2
const int PADDLE1_X = 50;
const int PADDLE2_X = WINDOW_WIDTH - 75;
// Paddle width and height
const int PADDLE_WIDTH = 20;
const int PADDLE_HEIGHT = 100;
// Speed of both players
const int PLAYER_SPEED = 0;
// Ball Speed -- this will not be constant
// The Ball Modifier will modify the speed based on the place it lands on the paddle
// Ball speed will never go under 10, and will accelerate over time
// Ball diameter
const int BALL_SPEED = 100;
const int BALL_MODIFIER = 5;
const int BALL_DIAMETER = 10;
const int BALL_CENTER_X = WINDOW_CENTER_X - BALL_DIAMETER;
const int BALL_CENTER_Y = WINDOW_CENTER_Y - BALL_DIAMETER;
const int LANG = 3;
const int LANG_ENGLISH = 3;
const int LANG_GERMAN = 4;
// Game Entity data structure
struct GameObject
{
SDL_Rect ScreenLocation;
SDL_Rect BitmapLocation;
int SpeedX;
int SpeedY;
};
// SDL stuff
SDL_Window* gWindow = NULL;
SDL_Renderer* gWindowRenderer;
SDL_Rect gScreen;
SDL_Event e;
// Game objects
GameObject gPlayer1; // Paddle 1
GameObject gPlayer2; // Paddle 2
GameObject gBall; // Ball
// Scores. I feel like it's better to leave them uninitialized.
int gPlayer1Score;
int gPlayer2Score;
void Render();
bool init();
bool GameQuit;
void Quit();
int main( int argc, char* argv[] )
{
// const Uint8* keyStates = SDL_GetKeyboardState(NULL);
if( init() == false )
{
std::cout << "Init failed. Bye bye!\n";
return 1;
}
while( !GameQuit )
{
const Uint8* keyStates = SDL_GetKeyboardState( NULL );
while( SDL_PollEvent( &e ) )
{
if( e.type == SDL_QUIT )
GameQuit = true;
if( e.type == SDL_KEYDOWN )
{
switch( e.key.keysym.scancode )
{
case SDL_SCANCODE_ESCAPE:
GameQuit = true;
break;
}
}
}
if( keyStates[ SDL_SCANCODE_UP ] )
{
gPlayer1.ScreenLocation.y -= PLAYER_SPEED;
}
if( keyStates[ SDL_SCANCODE_DOWN ] )
{
gPlayer1.ScreenLocation.y += PLAYER_SPEED;
}
if( keyStates[ SDL_SCANCODE_W ] )
{
gPlayer2.ScreenLocation.y -= PLAYER_SPEED;
}
if( keyStates[ SDL_SCANCODE_S ] )
{
gPlayer2.ScreenLocation.y += PLAYER_SPEED;
}
Render();
}
Quit();
return 0;
}
bool init()
{
bool success = true;
if( SDL_Init( SDL_INIT_VIDEO < 0 ) )
{
success = false;
return success;
}
if( TTF_Init() < 0 )
{
success = false;
return success;
}
srand( time( NULL ) ); // Seed rng
// From SDL_Rect.h
// 64 typedef struct SDL_Rect
// 65 {
// 66 int x, y;
// 67 int w, h;
// 68 } SDL_Rect;
GameQuit = false;
gPlayer1.ScreenLocation.y = ( ( WINDOW_HEIGHT / 2 ) - ( PADDLE_HEIGHT / 2 ) );
gPlayer1.ScreenLocation.x = PADDLE1_X;
gPlayer1.ScreenLocation.w = PADDLE_WIDTH;
gPlayer1.ScreenLocation.h = PADDLE_HEIGHT;
gPlayer2.ScreenLocation.y = ( ( WINDOW_HEIGHT / 2 ) - ( PADDLE_HEIGHT / 2 ) );
gPlayer2.ScreenLocation.x = PADDLE2_X;
gPlayer2.ScreenLocation.w = PADDLE_WIDTH;
gPlayer2.ScreenLocation.h = PADDLE_HEIGHT;
gBall.ScreenLocation.x = BALL_CENTER_X;
gBall.ScreenLocation.y = BALL_CENTER_Y;
gBall.ScreenLocation.w = BALL_DIAMETER;
gBall.ScreenLocation.h = BALL_DIAMETER;
gPlayer1.BitmapLocation.x = PADDLE_BITMAP_X;
gPlayer1.BitmapLocation.y = PADDLE_BITMAP_Y;
gPlayer1.BitmapLocation.w = PADDLE_WIDTH;
gPlayer1.BitmapLocation.h = PADDLE_HEIGHT;
gPlayer2.BitmapLocation.x = PADDLE_BITMAP_X;
gPlayer2.BitmapLocation.y = PADDLE_BITMAP_Y;
gPlayer2.BitmapLocation.w = PADDLE_WIDTH;
gPlayer2.BitmapLocation.h = PADDLE_HEIGHT;
gBall.BitmapLocation.x = BALL_BITMAP_X;
gBall.BitmapLocation.y = BALL_BITMAP_Y;
gBall.BitmapLocation.w = BALL_DIAMETER;
gBall.BitmapLocation.h = BALL_DIAMETER;
gPlayer1.SpeedY = PLAYER_SPEED;
gPlayer1.SpeedX = 0;
gPlayer2.SpeedY = PLAYER_SPEED;
gPlayer2.SpeedX = 0;
gPlayer1Score = 0;
gPlayer2Score = 0;
gScreen.x = 0;
gScreen.y = 0;
gScreen.w = WINDOW_WIDTH;
gScreen.h = WINDOW_HEIGHT;
// Note to self: Leave this out since color keying NULL will segfault.
// SDL_SetColorKey(gBitmap, SDL_TRUE, SDL_MapRGB(gBitmap->format, 255, 0, 255));
gWindow = SDL_CreateWindow(
WINDOW_TITLE,
SDL_WINDOWPOS_UNDEFINED,
SDL_WINDOWPOS_UNDEFINED,
WINDOW_WIDTH,
WINDOW_HEIGHT,
SDL_WINDOW_MAXIMIZED );
// Render SDL Window
gWindowRenderer = SDL_CreateRenderer( gWindow, -1, 0 );
if( gWindowRenderer == nullptr )
{
success = false;
return success;
}
SDL_RenderSetLogicalSize( gWindowRenderer, WINDOW_WIDTH, WINDOW_HEIGHT );
SDL_SetRenderDrawColor( gWindowRenderer, 0x00, 0x00, 0x00, 0xFF );
return success;
}
// Display Menu Text
bool Menu()
{
bool success = false;
if( LANG == LANG_ENGLISH )
{
// DisplayText("Start (G)ame", 350, 250, 12, 255, 255, 255);
// DisplayText("(Q)uit Game", 350, 270, 12, 255, 255, 255);
success = true;
return success;
}
else if( LANG == LANG_GERMAN )
{
// DisplayText("(G) Spielen", 350, 270, 12, 255, 255, 255);
// DisplayText("(Q) Spiel verlassen", 350, 270, 12, 255, 255, 255);
success = true;
return success;
}
else
{
return success;
}
}
void Render()
{
SDL_RenderClear( gWindowRenderer );
SDL_SetRenderDrawColor( gWindowRenderer, 0x00, 0x00, 0x00, 0xFF );
SDL_RenderFillRect( gWindowRenderer, &gScreen );
SDL_SetRenderDrawColor( gWindowRenderer, 0xFF, 0xFF, 0xFF, 0xFF );
SDL_RenderFillRect( gWindowRenderer, &gPlayer1.ScreenLocation );
SDL_RenderFillRect( gWindowRenderer, &gPlayer2.ScreenLocation );
SDL_RenderFillRect( gWindowRenderer, &gBall.ScreenLocation );
SDL_RenderPresent( gWindowRenderer );
}
void Quit()
{
SDL_DestroyWindow( gWindow );
SDL_Quit();
}
I'm not sure what I'm doing wrong and would appreciate a concise answer.
Thank you for your time.

Answer 1

Builds & runs fine on my Debian 10 system, though PLAYER_SPEED is zero so nothing useful happens to gPlayer1.ScreenLocation.y/gPlayer2.ScreenLocation.y in the keyStates if-blocks.
Setting PLAYER_SPEED to something other than zero fixes that on my end.