29 The Power of Inheritance and Polymorphism

Inheritance and Polymorphism 1046}}WindowRep::Instance()->PutCharacter(ch, x + fX, y + fY);x--;y--;fCurrentImg[y][x] = ch;Note the call to WindowRep::Instance(). This returns a WindowRep* pointer.The WindowRep referenced by this pointer is then asked to output the character atthe specified point as offset by the origin of this window.Function SetBkgd() simply validates the coordinate arguments and then sets acharacter in the background array. Function Get() returns the character at aparticular point in either background of foreground array (an example of its use isin the statement Get(x, y, fBkgd) in Window::Clear()).char Window::Get(int x, int y, char **img) const{x--;y--;return img[y][x];}Function PrepareContent() loads the current image array from the backgroundand, if appropriate, calls SetFrame() to add a frame.void Window::PrepareContent(){for(int row = 0; row < fHeight; row++)for(int col = 0; col < fWidth; col++)fCurrentImg[row][col] = fBkgd[row][col];if(fFramed)SetFrame();}void Window::SetFrame(){for(int x=1; x