Object-oriented Software in Ada 95

TUI the implementation 333
23.2.4 The class Screen
The package Class_screen implements cursor positioning and output to an ANSI compatible display screen.
The responsibilities of the class are:
Method
Clear_Screen
Position_Cursor
Put
Responsibility
Clears all the screen.
Position the cursor at x, y on the screen.
Write information to the current position on the screen.
Note: The co-ordinate system for the screen is shown in Figure 23.3.
1,1 80,1
y
x
1,24 80,24
Figure 23.3 Co-ordinate system for the screen.
The class specification for Class_screen is:
package Class_Screen is
procedure Put( Ch :in Character ); --Put char
procedure Put( Str:in String ); --Put string
procedure Clear_Screen; --Clear screen
procedure Position_Cursor(Col:in Positive; Row:in Positive);
private
end Class_Screen;
Note:
As there is only one instance of a screen the class Screen contains all class methods.
The implementation of the class Screen uses the standard ANSI escape sequence to position the cursor onto
a text terminal. The overloaded procedures put call the relevant put procedure in Pack_md_io.
with Pack_Md_Io; use Pack_Md_Io;
package body Class_Screen is
Prefix: constant String := Character'Val(27) & "[";
procedure Put( N:in Positive ); --Write decimal number
procedure Put( Ch :in Character ) is
begin
Pack_Md_Io.Put( Ch );
end Put;
procedure Put( Str:in String ) is
begin
Pack_Md_Io.Put( Str );
end Put;
If an ANSI terminal is not available then the bodies of the procedures Clear_Screen and
Position_Cursor will need to be amended to reflect the characteristics of the user's terminal or output
environment.
© M A Smith - May not be reproduced without permission