[Coco] real-time mouse cursor

[Robert Gault]

Roger Taylor wrote:

> What I'm seeing is the cursor appears 
> only for about the top 1/3rd of the screen (actually less), and while it 
> moves out of this range, up or down, you can see the bottom of the 
> cursor start to fade away (to the background image) and the top portion 
> of the cursor reduces in sprite lines as the cursor moves away from the 
> visible part of the screen I mentioned.  In other words, the cursor 
> loses bottom lines as it moves out of the visible range I'm obtaining.
> 

I want to be sure I understand this description. You can move the cursor 
over the entire screen without losing it. However, the size of the 
cursor shrinks in the lower 2/3rds of the screen.

If the above is correct, that sounds like a code/math error rather than 
not enough time to update the cursor.

If the cursor can't be seen at all in the lower part of the screen, that 
  again sounds more like a math error rather than timing.

I would expect insufficient update time to cause jerky movement and 
perhaps flickering but not inability to cover the entire screen.

====================

The number of CPU cycles per H-scanline will depend on the size of the 
screen. The vertical blanking pulse may change size depending on the 
screen size as might the horizontal pulse. Determining the exact values 
for 320x200 (if that is the size you are using) probably can be done 
experimentally with a program. If not, a high quality oscilloscope will 
be required.

There is some data in the MESS source code and Sockmaster probably knows 
some of this information.