29 The Power of Inheritance and Polymorphism

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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
Implementation: Windows classes 1047perimeter points. (The input file for the map could define the perimeter as all"wall".)The access functions like X(), Y(), Height() etc are all trivial, e.g.:int Window::X() const{return fX;}The functions ShowAll() and ShowContent() are similar. They have loopstake characters from the current image and send the to the WindowRep object fordisplay. The only difference between the functions is in the loop limits; functionShowContent() does not display the periphery of a framed window.void Window::ShowAll() const{for(int row=1;row 0) && (s < (width-5)))SetLabel(s, label);PrepareContent();ShowValue();}(Note how arguments are passed to the base class constructor.)Function SetLabel() copies the label into the left portion of the backgroundimage. Function SetVal() simply changes the fVal data member then callsShowValue().void NumberItem::SetLabel(int s, char * l){fLabelWidth = s;
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29 The Power of Inheritance and Polymorphism

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