Lesson 1: Bresenham’s Line Drawing Algorithm

  1.

void line(int x0, int y0, int x1, int y1, TGAImage &image, TGAColor color) { 
    for (float t=0.; t<1.; t+=.01) { 
        int x = x0*(1.-t) + x1*t; 
        int y = y0*(1.-t) + y1*t; 
        image.set(x, y, color); 
    } 

}

2.

void line(int x0, int y0, int x1, int y1, TGAImage &image, TGAColor color) { 
    for (int x=x0; x<=x1; x++) { 
        float t = (x-x0)/(float)(x1-x0); 
        int y = y0*(1.-t) + y1*t; 
        image.set(x, y, color); 
    } 
}

3.

void line(int x0, int y0, int x1, int y1, TGAImage &image, TGAColor color) { 
    bool steep = false; 
    if (std::abs(x0-x1)<std::abs(y0-y1)) { // if the line is steep, we transpose the image 
        std::swap(x0, y0); 
        std::swap(x1, y1); 
        steep = true; 
    } 
    if (x0>x1) { // make it left−to−right 
        std::swap(x0, x1); 
        std::swap(y0, y1); 
    } 
    for (int x=x0; x<=x1; x++) { 
        float t = (x-x0)/(float)(x1-x0); 
        int y = y0*(1.-t) + y1*t; 
        if (steep) { 
            image.set(y, x, color); // if transposed, de−transpose 
        } else { 
            image.set(x, y, color); 
        } 
    } 
}

4.

void line(int x0, int y0, int x1, int y1, TGAImage &image, TGAColor color) { 
    bool steep = false; 
    if (std::abs(x0-x1)<std::abs(y0-y1)) { 
        std::swap(x0, y0); 
        std::swap(x1, y1); 
        steep = true; 
    } 
    if (x0>x1) { 
        std::swap(x0, x1); 
        std::swap(y0, y1); 
    } 
    int dx = x1-x0; 
    int dy = y1-y0; 
    float derror = std::abs(dy/float(dx)); 
    float error = 0; 
    int y = y0; 
    for (int x=x0; x<=x1; x++) { 
        if (steep) { 
            image.set(y, x, color); 
        } else { 
            image.set(x, y, color); 
        } 
        error += derror; 
        if (error>.5) { 
            y += (y1>y0?1:-1); 
            error -= 1.; 
        } 
    } 
} 

5.

void line(int x0, int y0, int x1, int y1, TGAImage &image, TGAColor color) { 
    bool steep = false; 
    if (std::abs(x0-x1)<std::abs(y0-y1)) { 
        std::swap(x0, y0); 
        std::swap(x1, y1); 
        steep = true; 
    } 
    if (x0>x1) { 
        std::swap(x0, x1); 
        std::swap(y0, y1); 
    } 
    int dx = x1-x0; 
    int dy = y1-y0; 
    int derror2 = std::abs(dy)*2; 
    int error2 = 0; 
    int y = y0; 
    for (int x=x0; x<=x1; x++) { 
        if (steep) { 
            image.set(y, x, color); 
        } else { 
            image.set(x, y, color); 
        } 
        error2 += derror2; 
        if (error2 > dx) { 
            y += (y1>y0?1:-1); 
            error2 -= dx*2; 
        } 
    } 
}