plot.c

#include <SDL3/SDL.h>
#include <stdio.h>
#include <stdbool.h>
#include <math.h>
#include "tinyexpr.h"

#define WIDTH 900
#define HEIGHT 600
#define X_MIN -10.0
#define X_MAX 10.0
#define Y_MIN -10.0
#define Y_MAX 10.0
#define STEP 0.01

void math_to_screen(double x, double y, int *screen_x, int *screen_y) {
    *screen_x = (int)((x - X_MIN) / (X_MAX - X_MIN) * WIDTH);
    *screen_y = (int)((Y_MAX - y) / (Y_MAX - Y_MIN) * HEIGHT);
}

void draw_line(SDL_Renderer *renderer, double x1, double y1, double x2, double y2, Uint8 r, Uint8 g, Uint8 b) {
    int sx1, sy1, sx2, sy2;
    math_to_screen(x1, y1, &sx1, &sy1);
    math_to_screen(x2, y2, &sx2, &sy2);
    
    SDL_SetRenderDrawColor(renderer, r, g, b, 255);
    SDL_RenderLine(renderer, sx1, sy1, sx2, sy2);
}

void draw_grid(SDL_Renderer *renderer) {
    SDL_SetRenderDrawColor(renderer, 64, 64, 64, 255);
    int y_axis_screen;
    int dummy;
    math_to_screen(0, 0, &dummy, &y_axis_screen);
    SDL_RenderLine(renderer, 0, y_axis_screen, WIDTH, y_axis_screen);
    
    int x_axis_screen;
    math_to_screen(0, 0, &x_axis_screen, &dummy);
    SDL_RenderLine(renderer, x_axis_screen, 0, x_axis_screen, HEIGHT);
    
    SDL_SetRenderDrawColor(renderer, 32, 32, 32, 255);
    
    for (int i = (int)X_MIN; i <= (int)X_MAX; i++) {
        if (i == 0) continue;
        int sx, sy1, sy2;
        math_to_screen(i, Y_MIN, &sx, &sy1);
        math_to_screen(i, Y_MAX, &sx, &sy2);
        SDL_RenderLine(renderer, sx, sy1, sx, sy2);
    }
    
    for (int i = (int)Y_MIN; i <= (int)Y_MAX; i++) {
        if (i == 0) continue;
        int sy, sx1, sx2;
        math_to_screen(X_MIN, i, &sx1, &sy);
        math_to_screen(X_MAX, i, &sx2, &sy);
        SDL_RenderLine(renderer, sx1, sy, sx2, sy);
    }
}

void draw_expression(SDL_Renderer *renderer, const char *expr) {
    double x;
    te_variable vars[] = {{"x", &x}};
    int err;
    te_expr *pexpr = te_compile(expr, vars, 1, &err);
    
    if (!pexpr) {
        fprintf(stderr, "Error parsing expression at position %d\n", err);
        return;
    }
    
    SDL_SetRenderDrawColor(renderer, 255, 255, 255, 255);
    
    double prev_x = X_MIN;
    double prev_y = te_eval(pexpr);
    bool prev_valid = isfinite(prev_y) && prev_y >= Y_MIN && prev_y <= Y_MAX;
    
    for (x = X_MIN + STEP; x <= X_MAX; x += STEP) {
        double y = te_eval(pexpr);
        bool curr_valid = isfinite(y) && y >= Y_MIN && y <= Y_MAX;
        
        if (prev_valid && curr_valid) {
            double dy = fabs(y - prev_y);
            if (dy < (Y_MAX - Y_MIN) * 0.1) {
                draw_line(renderer, prev_x, prev_y, x, y, 255, 255, 255);
            }
        }
        
        prev_x = x;
        prev_y = y;
        prev_valid = curr_valid;
    }
    
    te_free(pexpr);
}

int main(int argc, char *argv[]) {
    if (argc != 2) {
        printf("Usage: %s <expression>\n", argv[0]);
        printf("Examples:\n");
        printf("  %s \"sin(x)\"\n", argv[0]);
        printf("  %s \"x^2\"\n", argv[0]);
        printf("  %s \"cos(x)*exp(-x/5)\"\n", argv[0]);
        return 1;
    }
    
    if (!SDL_Init(SDL_INIT_VIDEO)) {
        fprintf(stderr, "SDL_Init failed: %s\n", SDL_GetError());
        return 1;
    }
    
    SDL_Window *window = SDL_CreateWindow(
        "Function Plotter",
        WIDTH, HEIGHT,
        SDL_WINDOW_HIGH_PIXEL_DENSITY
    );
    
    if (!window) {
        fprintf(stderr, "SDL_CreateWindow failed: %s\n", SDL_GetError());
        SDL_Quit();
        return 1;
    }
    
    SDL_SetWindowPosition(window, SDL_WINDOWPOS_CENTERED, SDL_WINDOWPOS_CENTERED);
    
    SDL_Renderer *renderer = SDL_CreateRenderer(window, NULL);
    if (!renderer) {
        fprintf(stderr, "SDL_CreateRenderer failed: %s\n", SDL_GetError());
        SDL_DestroyWindow(window);
        SDL_Quit();
        return 1;
    }
    
    bool running = true;
    SDL_Event event;
    
    while (running) {
        while (SDL_PollEvent(&event)) {
            if (event.type == SDL_EVENT_QUIT) {
                running = false;
            }
        }
        
        SDL_SetRenderDrawColor(renderer, 0, 0, 0, 255);
        SDL_RenderClear(renderer);
        
        draw_grid(renderer);
        draw_expression(renderer, argv[1]);
        
        SDL_RenderPresent(renderer);
        
        SDL_Delay(16); 
    }
    
    SDL_DestroyRenderer(renderer);
    SDL_DestroyWindow(window);
    SDL_Quit();
    
    return 0;
}