用c语言写一个x轴刻度为时间，y轴刻度为数据的实时曲线波形demo

这个任务需要用到图形库，比如OpenGL或者SDL2，因为C语言本身并没有提供绘图功能。我以SDL2为例，给出一个基本的实时曲线波形demo：

#include <stdio.h>
#include <stdlib.h>
#include <SDL2/SDL.h>

#define WIDTH 640
#define HEIGHT 480
#define MAX_POINTS 100

typedef struct {
    float x, y;
} Point;

int main(int argc, char *argv[]) {
    SDL_Window *window;
    SDL_Renderer *renderer;
    SDL_Event event;
    Point points[MAX_POINTS];
    int i, num_points = 0;
    float y_scale, x_scale;
    Uint32 last_time = SDL_GetTicks();
    Uint32 current_time, delta_time;
    float t = 0, dt = 0.01;

    if (SDL_Init(SDL_INIT_VIDEO) != 0) {
        fprintf(stderr, "SDL_Init Error: %s\n", SDL_GetError());
        return EXIT_FAILURE;
    }

    window = SDL_CreateWindow("Real-time Plot", SDL_WINDOWPOS_UNDEFINED, SDL_WINDOWPOS_UNDEFINED, WIDTH, HEIGHT, SDL_WINDOW_SHOWN);
    if (window == NULL) {
        fprintf(stderr, "SDL_CreateWindow Error: %s\n", SDL_GetError());
        SDL_Quit();
        return EXIT_FAILURE;
    }

    renderer = SDL_CreateRenderer(window, -1, SDL_RENDERER_ACCELERATED | SDL_RENDERER_PRESENTVSYNC);
    if (renderer == NULL) {
        SDL_DestroyWindow(window);
        fprintf(stderr, "SDL_CreateRenderer Error: %s\n", SDL_GetError());
        SDL_Quit();
        return EXIT_FAILURE;
    }

    y_scale = HEIGHT / 2.0;
    x_scale = WIDTH / (float)MAX_POINTS;

    while (1) {
        current_time = SDL_GetTicks();
        delta_time = current_time - last_time;
        last_time = current_time;

        while (SDL_PollEvent(&event)) {
            if (event.type == SDL_QUIT) {
                SDL_DestroyRenderer(renderer);
                SDL_DestroyWindow(window);
                SDL_Quit();
                return EXIT_SUCCESS;
            }
        }

        points[num_points].x = num_points * x_scale;
        points[num_points].y = y_scale * (1 + sin(t));
        num_points = (num_points + 1) % MAX_POINTS;

        SDL_SetRenderDrawColor(renderer, 0, 0, 0, 255);
        SDL_RenderClear(renderer);

        SDL_SetRenderDrawColor(renderer, 255, 255, 255, 255);
        for (i = 0; i < num_points; i++) {
            SDL_RenderDrawPoint(renderer, points[i].x, HEIGHT - points[i].y);
        }

        SDL_RenderPresent(renderer);

        t += dt;
        SDL_Delay(10);
    }
}

这个demo使用了SDL2库来创建窗口和渲染器，并且每10毫秒更新一次绘图。

我们将y轴的刻度范围设置为[-1, 1]，然后将[-1, 1]映射到[0, HEIGHT/2]。x轴的刻度范围为[MAX_POINTS]，然后将[0, MAX_POINTS]映射到[0, WIDTH]。

每次更新时，我们添加一个新的点到数组中，同时删除最早的点。然后我们使用SDL_RenderDrawPoint()函数将所有点绘制到屏幕上。

最后，我们使用SDL_Delay()函数来控制更新速率，以保证每10毫秒更新一次。