Technical Q&As

OPS 13 - Determining if the Cursor is Hidden Or Not (27-September-96)

Q How do you determine whether the cursor is hidden or not?

A Currently the best way to determine that is to use a low memory global that has been removed from LowMem.h. The reason that it has been removed is that future OS may handle this differently.

Using low-memory globals has never really been approved of but in older interface files, they were documented. However the Universal Interfaces were designed as a way ahead into future operating systems. Access to some low-mems were changed to accessor functions for safety and others were removed. Therefore this means the low-mems without functions were felt to be changeable and no longer safe to use.

The following definitions were taken from an older Interface file:

enum {
    CrsrRect = 0x83C,   /*[GLOBAL VAR]  Cursor hit rectangle [8 bytes]*/
    TheCrsr  = 0x844,   /*[GLOBAL VAR]  Cursor data, mask & hotspot [68 bytes]*/
    CrsrAddr = 0x888,   /*[GLOBAL VAR]  Address of data under cursor [long]*/
    CrsrSave = 0x88C,   /*[GLOBAL VAR]  data under the cursor [64 bytes]*/
    CrsrVis  = 0x8CC,   /*[GLOBAL VAR]  Cursor visible? [byte]*/
    CrsrBusy = 0x8CD,   /*[GLOBAL VAR]  Cursor locked out? [byte]*/
    CrsrNew  = 0x8CE,   /*[GLOBAL VAR]  Cursor changed? [byte]*/
    CrsrState = 0x8D0,  /*[GLOBAL VAR]  Cursor nesting level [word]*/
    CrsrObscure = 0x8D2 /*[GLOBAL VAR]  Cursor obscure semaphore [byte]*/
  };

As you can see, CrsrVis is a flag that tells whether the cursor is hidden or not.

The following routine uses this flag to determine the hidden state of the cursor.

int IsCursorHidden()
{
	int retVal = 0;
    unsigned char cursorVisible;
 
    cursorVisible = *(unsigned char*)CrsrVis;
    if (cursorVisible)
        retVal = 0;
    else
        retVal = 1;
    return (retVal);
}

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