2D Transformations (POLYGON)

//2D Transformations (POLYGON)
#include<stdio.h>
#include<conio.h>
#include<math.h>
#include<graphics.h>
#include<dos.h>
struct wct
{
	int x;
	int y;
};
typedef double matrix[3][3];
matrix thm;

void setid(matrix m)
{
	int i,j;
	for(i=0;i<3;i++)
	for(j=0;j<3;j++)
		m[i][j]=(i=j);
}
void premul(matrix a)
{
	matrix tmp;
	int r,c;
	for(r=0;r<3;r++)
	for(c=0;c<3;c++)
		tmp[r][c]=thm[r][0]*a[0][c]+thm[r][1]*a[1][c]+thm[r][2]*a[2][c];
	for(r=0;r<3;r++)
	for(c=0;c<3;c++)
		thm[r][c]=tmp[r][c];
}
void transform(int n,wct *pt)
{
	int i;
	double tmp;
	for(i=0;i<n;i++)>
	{
		tmp=thm[0][0]*pt[i].x+thm[0][1]*pt[i].y+thm[0][2];
		pt[i].y=thm[1][0]*pt[i].x+thm[1][1]*pt[i].y+thm[1][2];
		pt[i].x=tmp;
	}
}
void translation(int tx,int ty)
{
	matrix m;
	setid(m);
	m[0][2]=tx;
	m[1][2]=ty;
	premul(m);
}
void rotation(double a,wct pt)
{
	matrix m;
	a=(22*a)/1260;
	setid(m);
	m[0][0]=cos(a);
	m[0][1]=sin(a);
	m[0][2]=pt.x*(1-cos(a))-pt.x*sin(a);
	m[1][0]=sin(a);
	m[1][1]=cos(a);
	m[1][2]=pt.y*(1-cos(a))-pt.x*sin(a);
	premul(m);
}
void scaling(int sx,int sy,wct pt)
{
	matrix m;
	setid(m);
	m[0][0]=sx;
	m[0][1]=pt.x*(1-sx);
	m[1][1]=sy;
	m[1][2]=pt.y*(1-sy);
	premul(m);
}
void usrpoly(wct *pt,int n)
{
	int i,j=0;
	int *a;
	for(i=0;i<n;i++)>
	{
		a[j]=pt[i].x;
		a[j+1]=pt[i].y;
		j+=2;
	}
	j-=2;
	a[j]=a[0];
	a[j+1]=a[1];
	drawpoly(n,a);
}
void main()
{
	int gd,gm,i,j;
	void translate(wct *,int);
	void rotate(wct *,int);
	void scale(wct *,int);
	void translation(int,int);
	wct pt[]={200,200,400,200,400,300,200,300,200,200};
	int tx,ty;
	int c;
	do
	{
		clrscr();
		printf("\n\t--------------------------- ");
		printf("\n\t 2d transformations(Polygon)");
		printf("\n\t--------------------------- ");
		printf("\n\t 1.Translation     ");
		printf("\n\t 2.Rotation        ");
		printf("\n\t 3.Scaling         ");
		printf("\n\t 4.Exit            ");
		printf("\n\t Enter your choice:");
		scanf("%d",&c);
		detectgraph(&gd,&gm);
		initgraph(&gd,&gm,"C:\\TC\\BGI");
		switch(c)
		{
			case 1: translate(pt,6);getch();break;
			case 2: rotate(pt,6);getch();break;
			case 3: scale(pt,6);getch();break;
			case 4: printf("\n\t\t Exit from the menu"); getch();break;
			default: printf("\n\t\t invalid choice........!");break;
		}
		getch();
		closegraph();
	}while(c!=4);
}
void translate(wct *pt,int n)
{
	int x,y;
	setid(thm);
	cleardevice();
	usrpoly(pt,n);
	printf("\t\t Enter point to translate (x,y):");
	scanf("%d%d",&x,&y);
	translation(x,y);
	transform(n,pt);
	usrpoly(pt,n);
}
void rotate(wct *pt,int n)
{
	double ang;
	wct rpt;
	setid(thm);
	usrpoly(pt,n);
	printf("\t\t Enter the angle to rotate");
	scanf("%f",&ang);
	printf("Enter the reference point(x,y)");
	scanf("%d%d",&rpt.x,&rpt.y);
	rotation(ang,rpt);
	transform(n,pt);
	usrpoly(pt,n);
}
void scale(wct *pt,int n)
{
	double ang;
	int sx,sy;
	wct rpt;
	setid(thm);
	usrpoly(pt,n);
	printf("\n\t Enter scaling factor (sx,sy)");
	scanf("%d%d",&sx,&sy);
	printf("Enter the reference point (x,y)");
	scanf("%d%d",&rpt.x,&rpt.y);
	scaling(sx,sy,rpt);
	transform(n,pt);
	usrpoly(pt,n);
}