isSprTile() and tiles offset

Me again!

I have a question regarding sprites and tile collision detection ( isSprTile() ).

Does the collision detection take the current tile offset into account?
If it does, that would be great.

However, I think it would also be useful (unless there's already another way to achieve this) to be able to explicitly specify the offset that should be used for the collision check.

In my current project, I'm using raster interrupts to implement parallax scrolling by changing the tile offsets on the fly.
When using raster interrupts, different parts of the screen may use different tile offsets.

In that situation, isSprTile() may not reliably determine the visible tile position.

This can lead to collisions being detected when, visually, there isn't one, or conversely, missing collisions that are clearly visible on screen.

Would it be possible to provide a version of the function where the tile offset (or scroll position) is passed explicitly as a parameter?

I hope I'm explaining this clearly. If not, please let me know and I'll try to explain it better.
 

Yes, currently the scrolling offsets are being taken into account for the test. Which means whenever the test occurs it looks at the scrolling register at that very moment to compute the collision, and as you mention the scrolling registers values can be different at that moment if raster interrupts are modifying them.

Well spotted !

I will see if I can add optionnal parameters as suggested.

Meanwhile you may want to use the isSprBox() or other solutions as a workaround.

Edit:
Looking at the code I realize the sprite collision position is wrong by one lowres pixel in each direction (due to a small hardware revision that was not propagated to the cpu code). Not a big deal, but I will correct for the next release.

Well, I tried, just after the vBlank(), setting the offset register to the "correct" value and just after calling the isSprTile().

Unfortunately, it doesn't seem working, as if the value I just set before calling isSprTile was ignored...

I will do a small test tomorrow and get back to you.

Here is a small example that shows sprite vs tile collision. Use cursors to change tile scrolling offsets.
The sprite collision box has been edited with SpritEd.

This at least validates that the underlying collision mecanism correctly takes the offsets into account.

 

Edit: forgot to tell to move the sprite with the mouse.

Thank you for the test program.
Yes, it works perfectly !

Well, I will try to find why in my dev, sometimes, collision is detected when, "visually" there is no.