High CPU usage with VSYNC turned ON in Opengl and SDL2 application - c++

Question

In this simple triangle drawing application made with opengl3.3 and sdl2, the cpu's usage shoots up to 50+% with vsync enabled. The vsync is enabled using SDL_GL_SetSwapInterval( 1 ). When i remove the vsync by setting the previous function to 0 and capped the fps to 60 manually in the main loop the cpu usage sits at around 5% average.
What is the problem here? Am i misunderstanding something fundamental here? below is my code. (The vsync function is in the initialize() loop provided below).
Main file:
unsigned int triangle_Gen()
{
float vertices[] = {
-0.5f, -0.5f, 0.0f, 1.0f, 0.0f, 0.0f,
0.0f, 0.5f, 0.0f, 0.0f, 1.0f, 0.0f,
0.5f, -0.5f, 0.0f, 0.0f, 0.0f, 1.0f,
};
unsigned int VBO, VAO;
glGenVertexArrays(1, &VAO);
glBindVertexArray(VAO);
glGenBuffers(1, &VBO);
glBindBuffer(GL_ARRAY_BUFFER, VBO);
glBufferData(GL_ARRAY_BUFFER, sizeof(vertices), vertices, GL_STATIC_DRAW);
glVertexAttribPointer(0, 3, GL_FLOAT, GL_FALSE, 6*sizeof(float), (void*)0);
glEnableVertexAttribArray(0);
glVertexAttribPointer(1, 3, GL_FLOAT, GL_FALSE, 6*sizeof(float), (void*)(3*sizeof(float)));
glEnableVertexAttribArray(1);
return VAO;
}
int main(int argc, char* args[])
{
float StartTicks = 0;
float EndTicks = 0;
float timeStep = 0;
int fps = 0;
float frameStartTime = 0;
float frameEndTime = 0;
float onesectime = 0;
bool enableEditor = false;
int editor_keyCount = 0;
if(!initialize())
{
std::cout<<"Failed to initiate instance!!!"<<std::endl;
}
else
{
std::cout << glGetString(GL_VERSION) <<std::endl;
int color_shaderProgram = Shaders("ShaderFiles/color_shader.vs","ShaderFiles/color_shader.fs");
unsigned int triangle = triangle_Gen();
glUseProgram(color_shaderProgram);
glBindVertexArray(triangle);
while(isRunning)
{
SDL_GetWindowSize(window, &SCREEN_WIDTH, &SCREEN_HEIGHT);
glViewport(0, 0, SCREEN_WIDTH, SCREEN_HEIGHT);
if(!enableEditor)
{ SDL_SetRelativeMouseMode(SDL_TRUE); } //disable cursor
else
{ SDL_SetRelativeMouseMode(SDL_FALSE); } //enable cursor
Uint32 time = 0;
time = SDL_GetTicks() - StartTicks;
timeStep = time/1000.f;
StartTicks = SDL_GetTicks();
fps++; //fps counter
onesectime += timeStep; //1 sec counter
frameStartTime = SDL_GetTicks();
//=========================================input handle sector =========================================//
while (SDL_PollEvent(&e) != 0)
{
if (e.type == SDL_QUIT)
isRunning = false;
if( e.type == SDL_KEYDOWN && e.key.repeat == 0 )
{
switch(e.key.keysym.sym)
{
case SDLK_e: editor_keyCount++; break;
}
if(editor_keyCount == 1)
{ enableEditor = !enableEditor; }
}
if( e.type == SDL_KEYUP && e.key.repeat == 0 )
{
switch(e.key.keysym.sym)
{
case SDLK_e: editor_keyCount--; break;
}
}
}
//=========================================render sector=========================================//
glClearColor(0.0f, 0.0f, 0.0f, 0.0f);
glClear(GL_COLOR_BUFFER_BIT);
glDrawArrays(GL_TRIANGLES, 0, 3);
//--------------------------------------fps stuff --------------------------------------------------------------//
frameEndTime = SDL_GetTicks();
/*if((frameEndTime - frameStartTime) < 16.67) //60fps manual cap
{
SDL_Delay(16.67-(frameEndTime-frameStartTime));
}*/
if(onesectime >= 1) //print fps
{
std::cout<<fps<<std::endl;
onesectime = 0;
fps = 0;
}
SDL_GL_SwapWindow( window );
}
}
close();
return 0;
}
initialize() function:
bool initialize()
{
Uint32 flags = SDL_INIT_TIMER | SDL_INIT_AUDIO | SDL_INIT_VIDEO | SDL_INIT_EVENTS;
//initializing
if(SDL_Init(flags) < 0)
{
std::cout<<"SDL could not initialize! SDL Error: " << SDL_GetError() << std::endl;
isRunning = false;
}
else
{
SDL_GL_SetAttribute( SDL_GL_CONTEXT_MAJOR_VERSION, 3 );
SDL_GL_SetAttribute( SDL_GL_CONTEXT_MINOR_VERSION, 3 );
flags = SDL_WINDOW_RESIZABLE | SDL_WINDOW_OPENGL | SDL_WINDOW_SHOWN;//SDL_WINDOW_INPUT_GRABBED;
window = SDL_CreateWindow("Test Application", SDL_WINDOWPOS_CENTERED, SDL_WINDOWPOS_CENTERED, SCREEN_WIDTH, SCREEN_HEIGHT, flags);
if( window == NULL )
{
std::cout<<"Window could not be created! SDL Error:" << SDL_GetError() << std::endl;
isRunning = false;
}
else
{
openGL_Context = SDL_GL_CreateContext( window );
if(openGL_Context == NULL)
{
std::cout<<"OpenGL context could not be created! SDL Error: %s\n" << SDL_GetError() <<std::endl;
isRunning = false;
}
else
{
//enable(1)or disable(0) vsync
if(SDL_GL_SetSwapInterval( 1 ) < 0)
{
std::cout<<"Warning, vsync disabled!"<<std::endl;
}
glewExperimental = GL_TRUE;
if( glewInit() != GLEW_OK)
{
std::cout<<"Unable to initialize glew!"<<std::endl;
isRunning = false;
}
else
{
SDL_WarpMouseInWindow(window, (SCREEN_WIDTH/2), (SCREEN_HEIGHT/2));
}
}
}
}
return isRunning;
}