Simple Line Drawing Algorithm using SDL

main.cpp

#include <SDL.h>
#include <stdio.h>
#include <string>

//Screen dimension constants
const int SCREEN_WIDTH = 640;
const int SCREEN_HEIGHT = 480;

//Starts up SDL and creates window
bool init();

//Frees media and shuts down SDL
void close();

// Draws the current frame
void draw();

//The window we'll be rendering to
SDL_Window* gWindow = NULL;

//The window renderer
SDL_Renderer* gRenderer = NULL;

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_SetRenderDrawColor(gRenderer, 0xFF, 0xFF, 0xFF, 0xFF);
            SDL_RenderClear(gRenderer);

            // draw the frame
            draw();

            //Update screen and wait for 100 ms
            SDL_RenderPresent(gRenderer);
            SDL_Delay(100);
        }
    }

    //Free resources and close SDL
    close();
    return 0;
}

bool init()
{
    //Initialize SDL
    if (SDL_Init(SDL_INIT_VIDEO) < 0)
    {
        printf("SDL could not initialize! SDL Error: %s\n", SDL_GetError());
        return false;
    }

    //Set texture filtering to linear
    if (!SDL_SetHint(SDL_HINT_RENDER_SCALE_QUALITY, "1"))
    {
        printf("Warning: Linear texture filtering not enabled!");
    }

    //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());
        return false;
    }

    //Create renderer for window
    gRenderer = SDL_CreateRenderer(gWindow, -1, SDL_RENDERER_ACCELERATED);
    if (gRenderer == NULL)
    {
        printf("Renderer could not be created! SDL Error: %s\n", SDL_GetError());
        return false;
    }

    //Initialize renderer color
    SDL_SetRenderDrawColor(gRenderer, 0xFF, 0xFF, 0xFF, 0xFF);

    return true;
}

void close()
{
    //Destroy window	
    SDL_DestroyRenderer(gRenderer);
    SDL_DestroyWindow(gWindow);
    gWindow = NULL;
    gRenderer = NULL;

    SDL_Quit();
}

int sign(float args)
{
    if (args < 0)
        return -1;
    else if (args > 0)
        return 1;
    else return 0;
}

void draw()
{
    int x = 0, y = 0, x1 = SCREEN_WIDTH / 2, y1 = SCREEN_HEIGHT;
    float l = abs(x1 - x) > abs(y1 - y) ? abs(x1 - x) : abs(y1 - y);

    float dx = (x1 - x) / l;
    float dy = (y1 - y) / l;

    float xinc = x + 0.5 * sign(dx);
    float yinc = y + 0.5 * sign(dy);

    // Set Draw color to Red
    SDL_SetRenderDrawColor(gRenderer, 0xFF, 0x00, 0x00, 0xFF);

    for (int i = 0; i <= l; i++)
    {
        SDL_RenderDrawPoint(gRenderer, abs(xinc), abs(yinc));
        xinc = abs(xinc + dx);
        yinc = abs(yinc + dy);
    }
}