Empty SDL2 window taking lots (40%+) GPU to render? - c++

Question

I've been trying to learn how to use SDL2, and am trying to follow the tutorials here for that. From example 7 (texture loading / hardware rendering), I've put together this stripped down example. As far as I can tell, the code is only calling SDL_RenderClear() and SDL_RenderPresent() in the render loop, VSYNC'd to my monitor (100 Hz in this case). However, I'm seeing Windows report 40% GPU utilization when doing this, which seems high for doing nothing. My GPU sits at 1-2% utilization when the SDL2 program is not running.
Removing just the SDL_RenderPresent() call brings the usage all the way down to 1-2% again, but then nothing gets drawn, which makes me think that the issue is either in SDL2's rendering, or (much more likely), how I've configured it.
Is this high GPU utilization (when doing nothing) expected? Is there anything I can do to minimize the GPU utilization (while still using hardware rendering)?
===================================
Machine details:
Windows 10
Threadripper 3970x CPU (3.7 GHz 32 core)
256 GB RAM DDR4 3200 MHz
1x RTX 3090 GPU
3x 1440p 100Hz monitors
GPU utilization (shown via Task Manager and Xbox Game Bar):
Code:
#define SDL_MAIN_HANDLED
/*This source code copyrighted by Lazy Foo' Productions (2004-2020)
and may not be redistributed without written permission.*/
// Using SDL, SDL_image, standard IO, and strings
#include <SDL.h>
#include <stdio.h>
#include <string>
// Screen dimension constants
const int SCREEN_WIDTH = 1920;
const int SCREEN_HEIGHT = 1080;
// Starts up SDL and creates window
bool init();
// Frees media and shuts down SDL
void close();
// The window we'll be rendering to
SDL_Window* gWindow = NULL;
// The window renderer
SDL_Renderer* gRenderer = NULL;
bool init() {
// Initialization flag
bool success = true;
// Initialize SDL
if (SDL_Init(SDL_INIT_VIDEO) < 0) {
printf("SDL could not initialize! SDL Error: %s\n", SDL_GetError());
success = false;
} else {
// Create window
gWindow = SDL_CreateWindow(
"SDL Tutorial",
SDL_WINDOWPOS_UNDEFINED,
SDL_WINDOWPOS_UNDEFINED,
SCREEN_WIDTH,
SCREEN_HEIGHT,
SDL_WINDOW_SHOWN);
if (gWindow == NULL) {
printf("Window could not be created! SDL Error: %s\n", SDL_GetError());
success = false;
} else {
// Create renderer for window
gRenderer =
SDL_CreateRenderer(gWindow, -1, SDL_RENDERER_ACCELERATED | SDL_RENDERER_PRESENTVSYNC);
if (gRenderer == NULL) {
printf("Renderer could not be created! SDL Error: %s\n", SDL_GetError());
success = false;
} else {
// Initialize renderer color
SDL_SetRenderDrawColor(gRenderer, 0xFF, 0x00, 0x00, 0x00);
}
}
}
return success;
}
void close() {
// Destroy window
SDL_DestroyRenderer(gRenderer);
SDL_DestroyWindow(gWindow);
gWindow = NULL;
gRenderer = NULL;
// Quit SDL subsystems
SDL_Quit();
}
int main(int argc, char* args[]) {
// Start up SDL and create window
if (!init()) {
printf("Failed to initialize!\n");
} else {
// Main loop flag
bool quit = false;
// Event handler
SDL_Event e;
// While application is running
while (!quit) {
// Handle events on queue
while (SDL_PollEvent(&e) != 0) {
// User requests quit
if (e.type == SDL_QUIT) {
quit = true;
}
}
// Clear screen
SDL_RenderClear(gRenderer);
//Update screen
SDL_RenderPresent( gRenderer );
}
}
// Free resources and close SDL
close();
return 0;
}