An experiment in drawing bitmapped lines on screen.

Draws a blue line from 0,0 to 240,0 and then increments 240,0 to 240,2 240,4 etc.

There are a couple of "gotchas" with working with bitmaps to be aware of.

1. Computing the bitmap to be drawn and then drawing it is much faster than drawing pixel by pixel or line by line. BMP_flip(); should be carefully positioned within the code loops to take this into account.

2. Bitmap mode expects colours to be defined as 8 bits. In essence, when selecting a pallet colour, we need to left shift the pallet number.

Explained helpfully on the SGDK discord thusly:

erik 22/06/2020 at 19:05
Because the bmp functions treat two hardware pixels as a single bitmap pixel
Each pixel is 4 bit color, so two at once means a byte, which is a lot more efficient to manipulate
But you also need to supply two colors

Stef 23/06/2020 at 11:39
as said Eric color are 4 bits on Megadrive, still i let the opportunity of providing a couple of pixel 
color instead of a single pixel color. Thus you can create mesh filling (alternate color pixel), to so 
pseudo transparent or just to simulate more colors.