Drawing a trapezoidal polygon in cocos2d

gistfile1.txt

static const CGFloat kPerspectiveAngle = 3;//3 degree rotation
#define PERSPECTIVE_CONSTRICT_PX_FOR_HEIGHT(h) roundf(tanf(kPerspectiveAngle / 180.f * M_PI)*h)


- (void)drawTerrainPolygon {
  static const int bottom = 23; // The padding at the bottom of the screen
  int constrict = PERSPECTIVE_CONSTRICT_PX_FOR_HEIGHT(self.contentSize.height);//Determine how many pixels to contract by
  CGPoint pts[] = { ccp(0,bottom),
    ccp(constrict,self.contentSize.height),
    ccp(self.contentSize.width-constrict,self.contentSize.height),
    ccp(self.contentSize.width,bottom) };
  glColorMask(TRUE, TRUE, TRUE, TRUE);
  ccDrawSolidPoly(pts, 4, ccc4FFromccc3B(self.backgroundColor));
}