Beyond Basic - Part 5

Written by: Tony Cruise

First Published: Micro’s Gazette – Issue 003 (May/June 1989)

This issue I will start to detail the collision detection routine to go with the automatic sprite routines from last issue.  But first here is a list of the conversions for SVI-318/328 to MSX.

Part 1

The SVI-318/328 use the port 8C to change slots.  So to change between the RAM and ROM slots use:

Part 2 Onwards

Here is a list of ROM calls, RAM locations and HOOK addresses to use instead of the MSX values.

• HGONE = FF57H,
• HTIMI = FF5AH,
• SCRMOD = FE3AH
• SETWRT = 373CH,
• SETRD = 3747H

Change the following port calls to:

• OUT (98H),A becomes OUT (80H),A
• IN A,(98H) becomes IN A,(84H)

This list will be expanded if necessary, each issue.

Sprite Collision Detection

Now onto this months routine.   Our routine will test the collision of one sprite (you specify) with all 31 others.  A table of flags will be used to show which sprites the one specified is colliding with.  The size of each sprite will be specified by a X and Y with from 0 to 15 (There is no zero width, work out the real value and subtract one).  For the routine to work effectively, your sprite shapes should be drawn from the top left hand corner of the sprite shape pattern.

e.g. X width 5, Y width 2

To make the routine easier to understand I have split it into two sections.  The section I will show this issue is the actual test routine, that tests whether two specified sprites are colliding and setting the carry flag if so.  The values of the registers on entry are:

• HL points to sprite 1 VRAM table location
• DE points to sprite 2 VRAM table location
• B lower 4 bits, y width and top 4 bits, x width for sprite 1
• C lower 4 bits, y width and top 4 bits, x width for sprite 2

Machine Code Program