Performance Issue
Not sure if this is a problem on my end, but here it goes.
I’m developing a 2D platformer using SDL. As I’m aiming low end hardware I chose SDL 1.2 and keep track of performance issues.
Before the update, the main window rendered on screen demanded between 0.1% and 0.5% of CPU usage. After the update, running the same built, it demands from 8% to 10% of CPU usage.
Without capping the framerate to 60FPS, before the update it demanded 12% of CPU usage. After the update it demands from 70% to 80% of CPU usage.
That’s a huge performance hit.
I tried to downgrade some packages like kernel, xorg-server, mesa and amd-ucode but problem persists.
CPU on this machine is an AMD FX-8370E.
Here is sample code to draw an SDL window on the screen. Those functions are split among many files in the real project, but for the sake of this example, I put everything in a single one. All it does is to draw an SDL window on the screen and handle a few inputs.
build command:
gcc -Wall -pedantic -O3 -lSDL -lm sdltest.c -o sdltest
The code is commented as didactic as possible because I’m considering opensource the game sometime after it’s release and want people to, not jus be able to port it to every platform under the sun, but also learn from it.
Try commenting the line CapFPS_(SDL_GetTicks()); at GameLoop_ function to see the CPU go nuts. 
/* --------------------------------------------------------------------------------------------- *
* My namespace:
* FunctionNames_ | _parameter_names | variable_names | s_structure_names | p_pointer_names
* g_globals
* --------------------------------------------------------------------------------------------- */
/* --------------------------------------------------------------------------------------------- *
* Libraries
* --------------------------------------------------------------------------------------------- */
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <stdbool.h>
#include <math.h>
#include <SDL/SDL.h>
#include <SDL/SDL_ttf.h>
#include <SDL/SDL_image.h>
#include <SDL/SDL_mixer.h>
/* --------------------------------------------------------------------------------------------- *
* Custom libraries
* --------------------------------------------------------------------------------------------- */
/* --------------------------------------------------------------------------------------------- *
* Globals * (Sorry, there are globals. I like them.) :-)
* --------------------------------------------------------------------------------------------- */
const int WINDOW_WIDTH = 640;
const int WINDOW_HEIGHT = 360;
const int SCREEN_BPP = 16;
bool g_quit_game = false;
SDL_Surface *g_main_window = NULL;
/* --------------------------------------------------------------------------------------------- *
* Macros
* --------------------------------------------------------------------------------------------- */
#define TICK_INTERVAL 16 // Used to cap FPS / Roughly 60 FPS
/* --------------------------------------------------------------------------------------------- *
* External entities
* --------------------------------------------------------------------------------------------- */
/* --------------------------------------------------------------------------------------------- *
* Variables and constants
* --------------------------------------------------------------------------------------------- */
/* --------------------------------------------------------------------------------------------- *
* Custom functions
* --------------------------------------------------------------------------------------------- */
bool BuildMainWindow_(void)
{
if (SDL_Init(SDL_INIT_EVERYTHING) != 0)
{
fprintf(stderr, "Error building main SDL window: %s\n", SDL_GetError());
return false;
}
SDL_WM_SetCaption ("Tito Deve Morrer!", NULL);
g_main_window = SDL_SetVideoMode
(
WINDOW_WIDTH,
WINDOW_HEIGHT,
SCREEN_BPP,
(SDL_HWSURFACE + SDL_DOUBLEBUF)
);
return true;
}
void ProcessInput_(void)
{
SDL_Event s_input_event;
SDL_PollEvent (&s_input_event);
if (s_input_event.type == SDL_QUIT) g_quit_game = true;
if (s_input_event.type == SDL_KEYDOWN)
{
switch (s_input_event.key.keysym.sym)
{
case SDLK_ESCAPE:
g_quit_game = true;
break;
case SDLK_RETURN:
SDL_WM_ToggleFullScreen(g_main_window);
break;
case SDLK_UP:
printf("UP was pressed!\n");
break;
case SDLK_DOWN:
printf("DOWN was pressed!\n");
break;
default:
break;
}
}
}
void CapFPS_(Uint32 _ticks)
{
// Outputs the frametime for debugging
// printf("Actual Ticks: %d, Ticks received from loop: %d, Delay time: %f\n",
// SDL_GetTicks(), _ticks, (float)(TICK_INTERVAL - (SDL_GetTicks() - _ticks)));
SDL_Delay(TICK_INTERVAL - (SDL_GetTicks() - _ticks));
}
/* --------------------------------------------------------------------------------------------- *
* Game loop
* --------------------------------------------------------------------------------------------- */
void GameLoop_(void)
{
while(!g_quit_game)
{
ProcessInput_();
// Updates the screen
SDL_Flip(g_main_window);
// Yields roughly 60fps to avoid screen tearing and save CPU load
CapFPS_(SDL_GetTicks());
}
}
/* --------------------------------------------------------------------------------------------- *
* Shut down
* --------------------------------------------------------------------------------------------- */
void ShutDown_(void)
{
printf("\nShutting the game down\n");
SDL_Quit();
}
/* --------------------------------------------------------------------------------------------- *
* Main
* --------------------------------------------------------------------------------------------- */
int main (void)
{
atexit(ShutDown_);
if (BuildMainWindow_())
{
GameLoop_();
}
return 0;
}
That’s it. I have no idea what could possibly be causing the issue. After the update it took a performance hit of 80% to 100%.
Thank you in advance.