SDL Geometry Example

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

#define SCREEN_WIDTH 640
#define SCREEN_HEIGHT 480

#define true (1)
#define false (0)
typedef unsigned char bool;

// Colour information
typedef struct {
    uint8_t r;
    uint8_t g;
    uint8_t b;
    uint8_t a;
} col_t;

// Like SDL_Rect, but for a line
typedef struct {
    int x1;
    int y1;
    int x2;
    int y2;
} line_t;

SDL_Window* window = NULL;
SDL_Renderer* renderer = NULL;

/* Function init
 * Initialises SDL, the window and the renderer and returns the success */

bool
init() {
    if (SDL_Init(SDL_INIT_VIDEO) < 0) {
        fprintf(stderr, "Error: SDL could not be initialised! SDL says: %s\n", SDL_GetError());
        return false;
    }

    // Try to set texture filtering to linear
    if (!SDL_SetHint(SDL_HINT_RENDER_SCALE_QUALITY, "1")) {
        printf("Warning: the texture filtering could not be set to linear.");
    }

    // Create the window
    window = SDL_CreateWindow(
        "Asteroids",
        SDL_WINDOWPOS_UNDEFINED,
        SDL_WINDOWPOS_UNDEFINED,
        SCREEN_WIDTH,
        SCREEN_HEIGHT,
        SDL_WINDOW_SHOWN
    );

    if (window == NULL) {
        fprintf(stderr, "Error: the window could not be created! SDL says: %s\n", SDL_GetError());
        return false;
    }

    // Create the renderer
    renderer = SDL_CreateRenderer(
        window,
        -1,
        SDL_RENDERER_ACCELERATED
    );

    if (renderer == NULL) {
        fprintf(stderr, "Error: the renderer could not be created! SDL says: %s\n", SDL_GetError());
        return false;
    }

    // Renderer colour
    if (
        SDL_SetRenderDrawColor(
            renderer,
            0xFF, 0xFF, 0xFF, 0xFF
        ) < 0
    ) {
        fprintf(stderr, "Error: the renderer colour could not be set! SDL says: %s\n", SDL_GetError());
        return false;
    }

    return true;
}

/* Function draw_rect
 * Draws a rectangle with the points contained in rect and returns the success. */

bool
draw_rect(
    SDL_Rect* rect, // contains the points of the rectangle
    bool fill
) {
    if (fill) {
        if (SDL_RenderFillRect(renderer, rect) < 0) {
            return false;
        }
    } else {
        if (SDL_RenderDrawRect(renderer, rect) < 0) {
            return false;
        }
    }

    return true;
}

/* Function draw_line
 * Draws a line on the screen with the points contained in line */

bool
draw_line(line_t* line) {
    if (
        SDL_RenderDrawLine(
            renderer,
            line->x1,
            line->y1,
            line->x2,
            line->y2
        ) < 0
    ) {
        return false;
    }

    return true;
}

/* Function free_sdl
 * Free memory and quit SDL subsystems. */

void
free_sdl() {
    SDL_DestroyRenderer(renderer);
    renderer = NULL;
    SDL_DestroyWindow(window);
    window = NULL;

    SDL_Quit();
}

/* Function set_colour
 * Sets the render colour based off of the col_t struct passed in. */

bool
set_colour(col_t* col) {
    if (
        SDL_SetRenderDrawColor(
            renderer,
            col->r,
            col->g,
            col->b,
            col->a
        ) < 0
    ) {
        return false;
    }

    return true;
}

int
main(void) {
    if (!init()) {
        return EXIT_FAILURE;
    }

    // Begin drawing

    if (SDL_RenderClear(renderer) < 0) {
        fprintf(stderr, "Error: could not clear the renderer! SDL says: %s\n", SDL_GetError());
        free_sdl();
        return EXIT_FAILURE;
    }

    // Red filled quad

    col_t col;

    col.r = 0xFF;
    col.g = 0x00;
    col.b = 0x00;
    col.a = 0xFF;

    if (!set_colour(&col)) {
        fprintf(stderr, "Error: could not set the renderer colour. SDL says: %s\n", SDL_GetError());
        free_sdl();
        return EXIT_FAILURE;
    }

    SDL_Rect rect;

    rect.x = SCREEN_WIDTH / 4;
    rect.y = SCREEN_HEIGHT / 4;
    rect.w = SCREEN_WIDTH / 2;
    rect.h = SCREEN_HEIGHT / 2;

    if (
        !draw_rect(
            &rect,
            true
        )
    ) {
        fprintf(stderr, "Error: could not draw the red filled quad. SDL says: %s\n", SDL_GetError());
        free_sdl();
        return EXIT_FAILURE;
    }

    // Outlined green quad

    col.r = 0x00;
    col.g = 0xFF;
    col.b = 0x00;
    col.a = 0xFF;

    if (!set_colour(&col)) {
        fprintf(stderr, "Error: could not set the renderer colour. SDL says: %s\n", SDL_GetError());
        free_sdl();
        return EXIT_FAILURE;
    }

    rect.x = SCREEN_WIDTH / 6;
    rect.y = SCREEN_HEIGHT / 6;
    rect.w = SCREEN_WIDTH * 2 / 3;
    rect.h = SCREEN_HEIGHT * 2 / 3;

    if (
        !draw_rect(
            &rect,
            false
        )
    ) {
        fprintf(stderr, "Error: could not draw the outline green quad. SDL says: %s\n", SDL_GetError());
        free_sdl();
        return EXIT_FAILURE;
    }

    // Blue horizontal line

    col.r = 0x00;
    col.g = 0x00;
    col.b = 0xFF;
    col.a = 0xFF;

    if (!set_colour(&col)) {
        fprintf(stderr, "Error: could not set the renderer colour. SDL says: %s\n", SDL_GetError());
        free_sdl();
        return EXIT_FAILURE;
    }

    line_t line;
    line.x1 = 0;
    line.y1 = SCREEN_HEIGHT / 2;
    line.x2 = SCREEN_WIDTH;
    line.y2 = SCREEN_HEIGHT / 2;

    if (!draw_line(&line)) {
        fprintf(stderr, "Error: could not draw the blue horizontal line. SDL says: %s\n", SDL_GetError());
        free_sdl();
        return EXIT_FAILURE;
    }

    // Vertical line of black dots

    col.r = 0x00;
    col.g = 0x00;
    col.b = 0x00;
    col.a = 0xFF;

    if (!set_colour(&col)) {
        fprintf(stderr, "Error: could not set the renderer colour. SDL says: %s\n", SDL_GetError());
        free_sdl();
        return EXIT_FAILURE;
    }

    for (int i = 0; i < SCREEN_HEIGHT; i += 4) {
        if (SDL_RenderDrawPoint(renderer, SCREEN_WIDTH / 2, i) < 0) {
            fprintf(stderr, "Error: could not one of the yellow points. SDL says: %s\n", SDL_GetError());
            free_sdl();
            return EXIT_FAILURE;
        }
    }

    SDL_RenderPresent(renderer); // Update the screen

    bool running = true;
    SDL_Event e;

    while (running) {
        // Handle events on queue
        while (SDL_PollEvent(&e) != 0) {
            if (e.type == SDL_QUIT) {
                running = false;
            }
        }
    }

    free_sdl();
    return EXIT_SUCCESS;
}