畫直線  水平夾角的   帶箭頭的

#include <graphics.h>
#include <math.h>


#define PI 3.14159265
static double degree_to_radian(double degree)
{
    double radian = degree * PI / 180.0;
    return radian;
}

static double   get_distance(double   start_x, double   start_y, double   end_x, double   end_y)
{
    double   result, sqrt_f;
    result = (start_x-end_x)*(start_x-end_x)+(start_y-end_y)*(start_y-end_y);
    sqrt_f = sqrt(result);
    return   sqrt_f;
}


static void draw_arraw_line_imp(double  s_x, double  s_y, double  e_x, double  e_y, double length, double angle)
{
    double   tmp_x;
    double   tmp_y;
    double   x1;
    double   y1;
    double   x2;
    double   y2;

    double distance = get_distance(s_x,s_y,e_x,e_y);

    tmp_x = e_x + (s_x-e_x)*length/distance;
    tmp_y = e_y + (s_y-e_y)*length/distance;
    x1 = (tmp_x-e_x)*cos(-angle/2) - (tmp_y-e_y)*sin(-angle/2) + e_x;
    y1 = (tmp_y-e_y)*cos(-angle/2) + (tmp_x-e_x)*sin(-angle/2) + e_y;
    x2 = (tmp_x-e_x)*cos(angle/2) - (tmp_y-e_y)*sin(angle/2) + e_x;
    y2 = (tmp_y-e_y)*cos(angle/2) + (tmp_x-e_x)*sin(angle/2) + e_y;

    line(x1, y1, e_x, e_y);
    line(x2, y2, e_x, e_y);
}

static draw_arraw_line(double  s_x, double  s_y, double  e_x, double  e_y)
{
    line(s_x, s_y, e_x, e_y);
    draw_arraw_line_imp(s_x, s_y, e_x, e_y, 15, degree_to_radian(20));
}


static void draw_arraw_line_with_angle(double start_x, double start_y, double length, double degree)
{
    double delt_x, delt_y, end_x, end_y, radian;

    radian = degree_to_radian(degree);
    delt_x = length * cos(radian);
    delt_y = length * sin(radian);

    end_x = start_x + delt_x;
    end_y = start_y - delt_y;

    draw_arraw_line(start_x, start_y, end_x, end_y);
}

int main()
{
    int   driver=DETECT;        
    int   mode;
    initgraph(&driver,&mode,"d://tc");      
    cleardevice();                    

    draw_arraw_line_with_angle(500, 300, 50, 30);
    draw_arraw_line_with_angle(500, 300, 50, 45);
    draw_arraw_line_with_angle(500, 300, 50, 90);
    draw_arraw_line_with_angle(500, 300, 50, 180);
    draw_arraw_line_with_angle(500, 300, 50, 270);
    draw_arraw_line_with_angle(500, 300, 50, 300);
    draw_arraw_line_with_angle(500, 300, 50, 10);
    draw_arraw_line_with_angle(500, 300, 50, 15);
    draw_arraw_line_with_angle(500, 300, 50, 20);
    draw_arraw_line_with_angle(500, 300, 50, 60);
    draw_arraw_line_with_angle(500, 300, 50, 80);
    getch();

    closegraph();                      
    return 0;
}