Lining Up Pixels vs Playfield

[Joel D. Park]

Guys,

 

I'm trying to do the basic math that will figure out where how a certain pixel on the screen would line up with a block on the playfield.

 

For example, the playfield is like 32 blocks wide and the screen is 150 pixels (or something like that) wide.

So a playfield block is every 4.68 pixels. I'm not exacly going to be able to do remainders/decimal math I don't think.

 

Have any of you guys allready come up with this calculation. I'm close with something like this:

temp1 = ballx/5 : temp2 = (bally - 39 ) / 8 + 5: pfpixel temp1 temp2 off

But for division reasons there are certain playfield blocks I can't hit.

 

Thanks,

Joel

[SeaGtGruff]

I'm trying to do the basic math that will figure out where how a certain pixel on the screen would line up with a block on the playfield.

 

For example, the playfield is like 32 blocks wide and the screen is 150 pixels (or something like that) wide.

So a playfield block is every 4.68 pixels. I'm not exacly going to be able to do remainders/decimal math I don't think.

 

Have any of you guys allready come up with this calculation. I'm close with something like this:

temp1 = ballx/5 : temp2 = (bally - 39 ) / 8 + 5: pfpixel temp1 temp2 off

But for division reasons there are certain playfield blocks I can't hit.

There are *160* pixel positions on a line, and *40* playfield blocks, so there's a playfield block every *4* pixel positions. So that means your first calculation is off a little (but this still isn't right, because there's more):

 

temp1 = ballx / 4 : rem not / 5

 

batari Basic normally uses only 32 of the 40 playfield blocks-- the leftmost 4 blocks and the rightmost 4 blocks are typically all blank-- so that means the usable portion of the playfield is 128 (32 * 4) pixel positions wide, with 16 (4 * 4) unused pixel positions on the left side of the screen, and another 16 (4 * 4) unused pixel positions on the right side of the screen. So that means if we number the first *usable* playfield block as 0 (as batari Basic does), then we need to subtract 16 from the pixel position before we divide by 4 (but this still isn't quite right, because there's more):

 

temp1 = (ballx - 16) / 4

 

Normally we number the pixel positions from 0 to 159. But because of the way batari Basic v1.0 calculates the ball's horizontal (x) position, the ball's pixel positions end up being numbered from 2 to 161. So that means we really need to subtract 18 (16 + 2) instead of 16:

 

temp1 = (ballx - 18) / 4

 

Try that and see if it works better for you.

 

Michael

[Joel D. Park]

This worked perfectly!!

 

Thank you!

Joel