Implement horizontal fine pixel tile scrolling

[cspang1]

Goal: ability to scroll background tiles smoothly horizontally, i.e. pixel-by-pixel. Could have system to allow for multiple different regions of different scroll rates. Primary goal however is to simply achieve fine scrolling.

Scrolling cannot be done on the CPU side - there's no way to de-conflict tile color palettes. So any fine scrolling must be done on the GPU side.

Horizontal scrolling will require some work - rendering tiles not on their boundaries results in needing to process an additional tile for each long of stored video data.

Planning out in scratchpad.

[cspang1]

Will need horizontal and vertical "position" tracking variables passed from CPU to control scrolling.

Hard-incremented on this line, as we will need the data for an extra tile during scrolling.

We instantiate a render cog internal tracker for which horizontal pixel we're rendering (curpx).

So the routine should operate as follows for horizontal fine scrolling (starting at the very beginning of a scanline):

1. We instantiate a variable curpx to track which physical pixel of the scanline we're currently rendering
2. We retrieve a variable h_pos from the graphics resources to determine what pixel of the tile map is aligned with the left side of our screen
3. We determine what our initial tile is by performing floor(h_pos/8), and load that tile's word to be processed.
4. We then determine what specific pixel from the tile palette we're processing by performing h_pos%8, and load that pixel for rendering. Pixels are stored in 0_1_2_3_4_5_6_7 order.
5. When we proceed to the next pixel, we first check that we've entered a new tile by checking whether curpx%8==0 checking whether our pixel buffer is empty. If so, we load the new tile and continue rendering pixels keeping track of how many pixels we've already pushed per tile
6. We repeat steps 4 and 5 until we have a long worth of graphics data to store, with the option of either breaking out of the process when we hit that or letting the buffer overflow to save cycles on all of the checks that would be performed

[cspang1]

Satisfied by 02e3e46