Program to illustrate the implementation of Y-Direction Shear Transformation

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

 void show_screen( );

 void apply_x_direction_shear(const int,int [],const float);
 void multiply_matrices(const float[3],const float[3][3],float[3]);

 void Polygon(const int,const int []);
 void Line(const int,const int,const int,const int);


 int main( )
    {
       int driver=VGA;
       int mode=VGAHI;

       initgraph(&driver,&mode,\"..\\\\Bgi\");

       show_screen( );

       int polygon_points[10]={ 220,190, 420,190, 420,290, 220,290, 220,190 };

       setcolor(15);
     Polygon(5,polygon_points);

       setcolor(15);
       settextstyle(0,0,1);
     outtextxy(50,415,\"*** Use Up and Down Arrow Keys to apply Y-Direction Shear.\");

       int key_code_1=0;
       int key_code_2=0;

       char Key_1=NULL;
       char Key_2=NULL;

       do
      {
         Key_1=NULL;
         Key_2=NULL;
         key_code_1=0;
         key_code_2=0;

         Key_1=getch( );
         key_code_1=int(Key_1);

         if(key_code_1==0)
        {
           Key_2=getch( );
           key_code_2=int(Key_2);
        }

         if(key_code_1==27)
        break;

         else if(key_code_1==0)
        {
           if(key_code_2==72)
              {
             setfillstyle(1,0);
               bar(40,70,600,410);

             apply_x_direction_shear(5,polygon_points,-0.1);

             setcolor(12);
               Polygon(5,polygon_points);
              }

           else if(key_code_2==80)
              {
             setfillstyle(1,0);
               bar(40,70,600,410);

             apply_x_direction_shear(5,polygon_points,0.1);

             setcolor(10);
               Polygon(5,polygon_points);
              }
        }
      }
       while(1);

       return 0;
    }



 //---------------------  apply_x_direction_shear( )  --------------------//


 void apply_x_direction_shear(const int n,int coordinates[],const float Sh_y)
    {
       for(int count=0;count<n;count++)
      {
         float matrix_a[3]={coordinates[(count*2)],
                         coordinates[((count*2)+1)],1};
         float matrix_b[3][3]={ {1,Sh_y,0} , {0,1,0} ,{ 0,0,1} };
         float matrix_c[3]={0};

         multiply_matrices(matrix_a,matrix_b,matrix_c);

         coordinates[(count*2)]=(matrix_c[0]+0.5);
         coordinates[((count*2)+1)]=(matrix_c[1]+0.5);
      }
    }

 /************************************************************************/
 //----------------------  multiply_matrices( )  ------------------------//
 /************************************************************************/

 void multiply_matrices(const float matrix_1[3],
                  const float matrix_2[3][3],float matrix_3[3])
    {
       for(int count_1=0;count_1<3;count_1++)
      {
         for(int count_2=0;count_2<3;count_2++)
        matrix_3[count_1]+=
               (matrix_1[count_2]*matrix_2[count_2][count_1]);
      }
    }


 //-----------------------------  Polygon( )  ----------------------------//


 void Polygon(const int n,const int coordinates[])
    {
       if(n>=2)
      {
         Line(coordinates[0],coordinates[1],
                         coordinates[2],coordinates[3]);

         for(int count=1;count<(n-1);count++)
        Line(coordinates[(count*2)],coordinates[((count*2)+1)],
                        coordinates[((count+1)*2)],
                        coordinates[(((count+1)*2)+1)]);
      }
    }


 //-------------------------------  Line( )  -----------------------------//


 void Line(const int x_1,const int y_1,const int x_2,const int y_2)
    {
       int color=getcolor( );

       int x1=x_1;
       int y1=y_1;

       int x2=x_2;
       int y2=y_2;

       if(x_1>x_2)
      {
         x1=x_2;
         y1=y_2;

         x2=x_1;
         y2=y_1;
      }

       int dx=abs(x2-x1);
       int dy=abs(y2-y1);
       int inc_dec=((y2>=y1)?1:-1);

       if(dx>dy)
      {
         int two_dy=(2*dy);
         int two_dy_dx=(2*(dy-dx));
         int p=((2*dy)-dx);

         int x=x1;
         int y=y1;

         putpixel(x,y,color);

         while(x<x2)
        {
           x++;

           if(p<0)
              p+=two_dy;

           else
              {
             y+=inc_dec;
             p+=two_dy_dx;
              }

           putpixel(x,y,color);
        }
      }

       else
      {
         int two_dx=(2*dx);
         int two_dx_dy=(2*(dx-dy));
         int p=((2*dx)-dy);

         int x=x1;
         int y=y1;

         putpixel(x,y,color);

         while(y!=y2)
        {
           y+=inc_dec;

           if(p<0)
              p+=two_dx;

           else
              {
             x++;
             p+=two_dx_dy;
              }

           putpixel(x,y,color);
        }
      }
    }


 //--------------------------  show_screen( )  ---------------------------//


 void show_screen( )
    {
       setfillstyle(1,1);
     bar(184,26,460,38);

       settextstyle(0,0,1);
     setcolor(15);
       outtextxy(5,5,\"******************************************************************************\");
       outtextxy(5,17,\"*-**************************************************************************-*\");
       outtextxy(5,29,\"*--------------------                                     -------------------*\");
       outtextxy(5,41,\"*-**************************************************************************-*\");
       outtextxy(5,53,\"*-**************************************************************************-*\");

     setcolor(11);
       outtextxy(194,29,\"Y-Direction Shear Transformation\");

     setcolor(15);

       for(int count=0;count<=30;count++)
          outtextxy(5,(65+(count*12)),\"*-*                                                                        *-*\");

       outtextxy(5,438,\"*-**************************************************************************-*\");
       outtextxy(5,450,\"*-------------------------                          -------------------------*\");
       outtextxy(5,462,\"******************************************************************************\");

     setcolor(12);
       outtextxy(229,450,\"Press any Key to exit.\");
    }