Horizontal Positioning Issue

[+Karl G]

I am seeing a discrepancy in where objects are positioned when looking in the Stella debugger vs where I think they should be positioned. In this project, I am positioning all 5 objects, and only one shows as the same position as I have set.

 

I have tried various versions of the SetHorizPos routine with the same results, so I assume the issue is elsewhere:

 

Player 0 position: 65 (Expected: 64)

Player 1 position: 76 (Expected: 76)

Missile 0 position: 23 (Expected: 24)

Missile 1 position: 134 (Expected: 135)

Ball position: 9 (Expected: 10)

Any idea what I am missing here? Thanks in advance for any advice.

3dpong.asm

[RevEng]

Here's the relevant info

 

It's just the normal offset for the positions of the objects. A RESP will set the objects position to the pixel at which the write happens. But the TIA needs a couple of cycles from the pixel clock to set up the actual output. Therefore all objects will be delayed by a couple of pixels.

 

The offset is 4 pixels for missiles and the ball, 5 pixels for single-width players, and 6 pixels for double- and quadrouple-width players. You need to take these offsets into account when calculating the position of an object.

This matches your -1 for missiles and ball, +1 for your wide player, using a regular player as the reference. All is well.

[+Karl G]

Thanks! This saves me from pulling out what remains of my hair. :-)