Simple sdl game very slow while cpu at 1.2% - c

Question

I wrote a simple 2d tile based game and ran it on 2 computers. On comp1 it's very slow, on comp2 it's lightening fast.
Comp1's cpu is a little slower, but it can play other sdl games (even inside emulaters) and simple 3d games, fast enough.
So I ran the game on both computers using only cpu rendering: both ran at the same speed.
Then I switched to gpu rendering and the 2nd computer went really fast (200+fps) but the first stayed at the same pace, around 20fps.
So I assumed either the hw acceleration is not working on comp1 or the cpu is clogged with my calculations.
I logged all the error handling and can confirm both computers support the hw acceleration and the texture sizes (i know this for a fact because the cpu bound version of the game has no flip and so the character always faces the same way ;)
So then it has to be a slow cpu on the first computer, right? But when I check the cpu stats the game only takes 1,2% cpu, and overall load is around 2% cpu
So the cpu is sitting mostly idle while my game crawls along :(
The game is a few 1000 lines of code now, so here are some of the statements that I think pertain to this problem:
Main game loop:
while (!quit)
{
GameEngine_Tick(gameType->fps, false, 0);
if (SDL_PollEvent(&event) != 0))
{
int windowID = event.window.windowID;
if (event.window.event == SDL_WINDOWEVENT_CLOSE &&
event.window.windowID == screens[0].windowID) quit = true;
switch (event.type)
{
case SDL_KEYDOWN:
if (event.key.keysym.sym == SDLK_LEFT) { Key_Left(); }
if (event.key.keysym.sym == SDLK_RIGHT) { Key_Right();}
if (event.key.keysym.sym == SDLK_UP) { Key_Up(); }
if (event.key.keysym.sym == SDLK_DOWN) { Key_Down(); }
break; // end key_down.
} // switch event type
}
GameEngine_Render();
}
Frame rate limiting in GameEngine_Tick:
void GameEngine_Tick(int fps, bool bIsRegTestStep, Uint8 TDir)
{
unsigned int frametime = 1000 / fps;
unsigned int currentTime;
const Uint8* keystates = SDL_GetKeyboardState(NULL); // do not free.
SDL_PumpEvents(); // upd keystates to get keyboard inputs.
// Get KB input - todo: later GetInputFromSelectedInputDevice (checks kb/xbox etc)
if (keystates[SDL_SCANCODE_LEFT]) GameLeft();
else if (keystates[SDL_SCANCODE_RIGHT]) GameRight();
Sprites_Tick();
// set framerate by waiting if needed.
currentTime = SDL_GetTicks();
if (currentTime - prevTime < (frametime))
{
//Sleep the remaining frame time
if (fps > 0) SDL_Delay((frametime)-(currentTime - prevTime)); /* fps-1 == MAX == no delay*/
}
prevTime = currentTime;
}
create renderer:
ren = nullptr;
if (bForceCPURender == false) ren = SDL_CreateRenderer(window, -1, SDL_RENDERER_ACCELERATED);// | SDL_RENDERER_PRESENTVSYNC);
if (nullptr == ren)
{
if (bForceCPURender == false)
{
Log("Info: SDL_CreateRenderer with SDL_RENDERER_ACCELERATED failed. Trying default.");
}
bForceCPURender = true;
ren = SDL_CreateRenderer(window, -1, 0);
if (nullptr == ren)
{
Log("Info: SDL_CreateRenderer with default also failed.");
SDLDestroy();
return -1;
}
else Logs("Info: success using default renderer.");
}
else Logs("Info: success, using SDL_CreateRenderer with SDL_RENDERER_ACCELERATED.");
Creating textures or surfaces:
spriteMapTexture = SDL_CreateTexture(ren, SDL_PIXELFORMAT_RGBA8888, SDL_TEXTUREACCESS_TARGET,
x_pixPerCharInStageMap * roomWidthInChars * gameRoomMatrix_w,
y_pixPerCharInStageMap * roomHeightInChars * gameRoomMatrix_h);
// If GPU cannot handle size of stage map: try to do CPU preRendering. (gpu is texture, cpu is surface).
if (NULL == spriteMapTexture || bForceCPUStageRenderAnyway == true)
{
spriteMapSurface = GameEngine_CreateRGBSurface(x_pixPerCharInStageMap * roomWidthInChars * gameRoomMatrix_w, y_pixPerCharInStageMap * roomHeightInChars * gameRoomMatrix_h);
}

Answer 1

while (!quit)
{
GameEngine_Tick(gameType->fps, false, 0);
if (SDL_PollEvent(&event) != 0))
^^ wat
{
// process event
}
GameEngine_Render();
}
Right now you're only processing a single event each frame. Used to be SDL could only buffer 128 events before dropping them, nowadays I think they're up to 64k. So if, for example, you have a high-report-rate gaming mouse (500-1000 Hz sampling) your event queue will get backed up far faster than a regular mouse (125 Hz). Same for any other event type SDL can generate; some systems will have different event generation rates than others.
You want to process every event in the queue before rendering a frame:
while (!quit)
{
GameEngine_Tick(gameType->fps, false, 0);
// NOTE: if -> while
while( SDL_PollEvent(&event) )
{
// process event
}
GameEngine_Render();
}