Programming and Graphics

7.3 A rotating polygon in animation 209

//--- Animation loop:

backbuffer(); // draw in the back buffer

repeat:

color(BLUE);

clear();

float dot = omega*Dt;

float cs = cos(dot);

float sn = sin(dot);

//--- Rotate the polygon by the angle dot around the rotation center:

for (int i=0; i<n; i++)

{

float xtemp = x[i]-xcrot;

float ytemp = y[i]-ycrot;

x[i] = xtemp*cs + ytemp*sn + xcrot;

y[i] = -xtemp*sn + ytemp*cs + ycrot;

points[i][0]=x[i];

points[i][1]=y[i];

}

//--- Paint the polygon:

color (RED);

poly2 (n,points);

//--- Swap the buffers:

swapbuffers();

//--- check the keyboard:

char kbd = char(checkkey()); // any key pressed?

//--- If s is pressed, wait for another key:

if(kbd == ’s’)

{

char kbd1 = char(getkey());

}

//--- If q is pressed, quit:

if(kbd == ’q’)