Yay

.gitmodules

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+[submodule "submodules/SDL_ttf"]
+	path = submodules/SDL_ttf
+	url = https://github.com/libsdl-org/SDL_ttf.git
+[submodule "submodules/SDL"]
+	path = submodules/SDL
+	url = https://github.com/libsdl-org/SDL.git
+

CMakeLists.txt

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+cmake_minimum_required(VERSION 3.30)
+
+project(SDL_FPSCounter C)
+
+add_subdirectory(src/)

src/CMakeLists.txt

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+add_library(SDL_FPSCounter STATIC SDL_FPSCounter.c)
+
+add_executable(fps-counter WIN32 main.c)
+target_link_libraries(fps-counter SDL_FPSCounter SDL3 SDL3_ttf)

src/SDL_FPSCounter.c

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+#include "SDL_FPSCounter.h"
+
+#include <stdlib.h>
+
+#include <SDL3/SDL.h>
+
+int SDL_CreateFPSCounter(SDL_FPSCounter* counter, uint32_t window_length)
+{
+	counter->window = malloc(sizeof(uint64_t) * window_length);
+	if (counter->window == NULL) {
+		SDL_OutOfMemory();
+		return -1;
+	}
+	memset(counter->window, 0, window_length * sizeof(uint64_t));
+	counter->frequency = SDL_GetPerformanceFrequency();
+	counter->window_index = 0;
+	counter->window_length = window_length;
+
+	return EXIT_SUCCESS;
+}
+
+void SDL_DestroyFPSCounter(SDL_FPSCounter* counter)
+{
+	free(counter->window);
+	memset(counter, 0, sizeof *counter);
+}
+
+int SDL_FPSCounterTick(SDL_FPSCounter* counter)
+{
+	counter->window[counter->window_index] = SDL_GetPerformanceCounter();
+	counter->window_index++;
+	counter->window_index = counter->window_index % counter->window_length;
+
+	return EXIT_SUCCESS;
+}
+
+uint64_t SDL_FPSCounterFPS(SDL_FPSCounter* counter)
+{
+	uint64_t last = counter->window[counter->window_index];
+	uint64_t current;
+	uint64_t acc_difference = 0;
+
+	for (uint32_t i = (counter->window_index + 1) % counter->window_length; i != counter->window_index; i = (i + 1) % counter->window_length) {
+		current = counter->window[i];
+		acc_difference += current - last;
+
+		last = current;
+	}
+
+	uint64_t average_difference = acc_difference / (counter->window_length - 1);
+	return counter->frequency / average_difference;
+}

src/SDL_FPSCounter.h

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+#ifndef SDL_FPSCOUNTER_H
+#define SDL_FPSCOUNTER_H
+
+#include <stdint.h>
+
+typedef struct SDL_FPSCounter_s {
+	uint64_t  frequency;
+	uint32_t  window_index;
+	uint32_t  window_length;
+	uint64_t* window;
+} SDL_FPSCounter;
+
+int  SDL_CreateFPSCounter(SDL_FPSCounter* counter, uint32_t window_length);
+void SDL_DestroyFPSCounter(SDL_FPSCounter* counter);
+
+int SDL_FPSCounterTick(SDL_FPSCounter* counter);
+uint64_t SDL_FPSCounterFPS(SDL_FPSCounter* counter);
+
+#endif

src/main.c

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+#include <SDL3/SDL.h>
+#include <SDL3/SDL_events.h>
+#include <SDL3/SDL_properties.h>
+#include <SDL3/SDL_render.h>
+#include <SDL3/SDL_surface.h>
+#include <SDL3_ttf/SDL_ttf.h>
+#include <stdbool.h>
+#include <stdlib.h>
+#include <stdio.h>
+
+#include "SDL_FPSCounter.h"
+
+#define INITIAL_WINDOW_HEIGHT 600
+#define INITIAL_WINDOW_WIDTH  600
+
+void DrawNumber(SDL_Window* window, SDL_Renderer* renderer, SDL_Texture* digits[10], int number)
+{
+	char number_string[snprintf(NULL, 0, "%i", number) + 1];
+	snprintf(number_string, sizeof(number_string), "%i", number);
+
+	int window_height, window_width;
+	SDL_GetWindowSize(window, &window_width, &window_height);
+
+	int current_x = 0;
+	char* digit_p = number_string;
+	for (; *digit_p; digit_p++) {
+		int index = (*digit_p) - '0';
+		SDL_Texture* digit_texture = digits[index];
+		SDL_FRect target_rect;
+		target_rect.x = current_x;
+		target_rect.y = 0;
+
+		SDL_GetTextureSize(digit_texture, &target_rect.w, &target_rect.h);
+
+		SDL_RenderTexture(renderer, digit_texture, NULL, &target_rect);
+
+		current_x += target_rect.w;
+	}
+}
+
+int main(int argc, char* argv[])
+{
+	(void) argc;
+	(void) argv;
+
+	SDL_Init( SDL_INIT_VIDEO | SDL_INIT_EVENTS);
+	if (TTF_Init()) {
+		fprintf(stderr, "Initializing SDL2_ttf failed: %s\n", SDL_GetError());
+	}
+
+	SDL_Window* window = SDL_CreateWindow(
+		"FPS-Counter",
+		INITIAL_WINDOW_WIDTH, INITIAL_WINDOW_HEIGHT,
+		0
+	);
+	if (window == NULL) {
+		fprintf(stderr, "Creating the window failed: %s\n", SDL_GetError());
+	}
+
+	SDL_Renderer* renderer = SDL_CreateRenderer(window, NULL);
+	if (renderer == NULL) {
+		fprintf(stderr, "Creating the window renderer failed: %s\n", SDL_GetError());
+	}
+
+
+	TTF_Font* number_font = TTF_OpenFont("/usr/share/fonts/urw-base35/NimbusMonoPS-Regular.otf", 300);
+	SDL_Texture* digits[10];
+	for (int i = 0; i < 10; i++) {
+		char string[3];
+		snprintf(string, 3, "%i", i);
+		SDL_Surface* digit_surface = TTF_RenderText_Solid(number_font, string, strlen(string),((SDL_Color) {0x2D, 0x2D, 0x2D, 0xFF}));
+		digits[i] = SDL_CreateTextureFromSurface(renderer, digit_surface);
+		SDL_DestroySurface(digit_surface);
+	}
+	TTF_CloseFont(number_font);
+
+
+	bool continue_ = true;
+	
+	SDL_FPSCounter fpscounter;
+	if (SDL_CreateFPSCounter(&fpscounter, 1000)) {
+		fprintf(stderr, "Failed to create fps counter: %s\n", SDL_GetError());
+		return 1;
+	}
+
+	while (continue_) {
+
+		SDL_Event event;
+		while(SDL_PollEvent(&event)) {
+			switch (event.type) {
+				case SDL_EVENT_QUIT:
+					continue_ = false;		
+					break;
+			}
+		}
+
+		SDL_SetRenderDrawColor(renderer, 0xFF, 0xC2, 0xDE, 0xFF);
+		SDL_RenderClear(renderer);
+
+		SDL_FPSCounterTick(&fpscounter);
+		DrawNumber(window, renderer, digits, SDL_FPSCounterFPS(&fpscounter));
+
+		SDL_RenderPresent(renderer);
+	}
+
+	SDL_DestroyFPSCounter(&fpscounter);
+	SDL_DestroyWindow(window);
+	SDL_Quit();
+
+	return EXIT_SUCCESS;
+}