Addressing (Rows, Columns, Positions)

The HACL provides two ways of addressing points (character positions) in the host presentation space. The application can address characters by row/column numbers, or by a single linear position value. Presentation space addressing is always 1-based (not zero-based) no matter what addressing scheme is used.

The row/column addressing scheme is useful for applications that relate directly to the physical screen presentation of the host data. The rectangular coordinate system (with row 1 column 1 in the upper left corner) is a natural way to address points on the screen. The linear positional addressing method (with position 1 in the upper left corner, progressing from left to right, top to bottom) is useful for applications that view the entire presentation space as a single array of data elements, or for applications ported from the EHLLAPI interface which uses this addressing scheme.

At the C++ layer, the different addressing schemes are chosen by calling different signatures for the same methods. For example, to move the host cursor to a given screen coordinate, the application can call the ECLPS::SetCursorPos method in one of two signatures:

PSObj->SetCusorPos(81);
PSObj->SetCursorPos(2, 1);

These statements have the same effect if the host screen is configured for 80 columns per row. This example also points out a subtle difference in the addressing schemes — the linear position method can yield unexpected results if the application makes assumptions about the number of characters per row of the presentation space. For example, the first line of code in the example would put the cursor at column 81 of row 1 in a presentation space configured for 132 columns. The second line of code would put the cursor at row 2 column 1 no matter what the configuration of the presentation space.