Q:

# Find the intersection point at the window boundary (base on region code)

``````// C++ program to implement Cohen Sutherland algorithm
// for line clipping.
#include <iostream>
using namespace std;

// Defining region codes
const int INSIDE = 0; // 0000
const int LEFT = 1; // 0001
const int RIGHT = 2; // 0010
const int BOTTOM = 4; // 0100
const int TOP = 8; // 1000

// Defining x_max, y_max and x_min, y_min for
// clipping rectangle. Since diagonal points are
// enough to define a rectangle
const int x_max = 10;
const int y_max = 8;
const int x_min = 4;
const int y_min = 4;

// Function to compute region code for a point(x, y)
int computeCode(double x, double y)
{
// initialized as being inside
int code = INSIDE;

if (x < x_min) // to the left of rectangle
code |= LEFT;
else if (x > x_max) // to the right of rectangle
code |= RIGHT;
if (y < y_min) // below the rectangle
code |= BOTTOM;
else if (y > y_max) // above the rectangle
code |= TOP;

return code;
}

// Implementing Cohen-Sutherland algorithm
// Clipping a line from P1 = (x2, y2) to P2 = (x2, y2)
void cohenSutherlandClip(double x1, double y1,
double x2, double y2)
{
// Compute region codes for P1, P2
int code1 = computeCode(x1, y1);
int code2 = computeCode(x2, y2);

// Initialize line as outside the rectangular window
bool accept = false;

while (true) {
if ((code1 == 0) && (code2 == 0)) {
// If both endpoints lie within rectangle
accept = true;
break;
}
else if (code1 & code2) {
// If both endpoints are outside rectangle,
// in same region
break;
}
else {
// Some segment of line lies within the
// rectangle
int code_out;
double x, y;

// At least one endpoint is outside the
// rectangle, pick it.
if (code1 != 0)
code_out = code1;
else
code_out = code2;

// Find intersection point;
// using formulas y = y1 + slope * (x - x1),
// x = x1 + (1 / slope) * (y - y1)
if (code_out & TOP) {
// point is above the clip rectangle
x = x1 + (x2 - x1) * (y_max - y1) / (y2 - y1);
y = y_max;
}
else if (code_out & BOTTOM) {
// point is below the rectangle
x = x1 + (x2 - x1) * (y_min - y1) / (y2 - y1);
y = y_min;
}
else if (code_out & RIGHT) {
// point is to the right of rectangle
y = y1 + (y2 - y1) * (x_max - x1) / (x2 - x1);
x = x_max;
}
else if (code_out & LEFT) {
// point is to the left of rectangle
y = y1 + (y2 - y1) * (x_min - x1) / (x2 - x1);
x = x_min;
}

// Now intersection point x, y is found
// We replace point outside rectangle
// by intersection point
if (code_out == code1) {
x1 = x;
y1 = y;
code1 = computeCode(x1, y1);
}
else {
x2 = x;
y2 = y;
code2 = computeCode(x2, y2);
}
}
}
if (accept) {
cout << "Line accepted from " << x1 << ", "
<< y1 << " to " << x2 << ", " << y2 << endl;
// Here the user can add code to display the rectangle
// along with the accepted (portion of) lines
}
else
cout << "Line rejected" << endl;
}

// Driver code
int main()
{
// First Line segment
// P11 = (5, 5), P12 = (7, 7)
cohenSutherlandClip(5, 5, 7, 7);

// Second Line segment
// P21 = (7, 9), P22 = (11, 4)
cohenSutherlandClip(7, 9, 11, 4);

// Third Line segment
// P31 = (1, 5), P32 = (4, 1)
cohenSutherlandClip(1, 5, 4, 1);

return 0;
}
``````
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