SP1 Scrolling: Test 2

It can be found in the src/sp1-sprites directory. It’s the previous Test 1 real scroller, but this time with sprites running all over the place, while the background is scrolling down.

The source is fully parameterized, so that different configurations can be tested and conclusions drawn.

The following parameters can be modified by just changing the #define’s at the top of the C file:

• Size and position of the scrolling area (dimensions in char cells)
• Number of pixels to scroll down on a single scroll cycle (pixels)
• Size of the top non-visible tile row - the one that brings new tiles from the game map (char cells). This is, practically, the size of the biggest tile in the map.
• Number of sprites (a maximum of 16 have been defined, but only the number #define’d will be used for the demo)

My findings so far:

• SP1 seems very capable of running a game with a scrolling background and several sprites moving on the screen
• The number of simultaneous sprites affects speed, but not as much as I expected. A possible explanation may be that since the whole scroll area is invalidated (currently) the drawing of all sprites does not invalidate more cells when more of them are on screen, so just their calculations and positioning matter.
• I have the definive impression that not using the HALT to wait for Vsync makes the demo go smoother (opinions?)

My next optimizations will be oriented to find the way of not invalidating all the screen, but only the affected cells. This will probably force me to keep track of the current tiles on screen and their position.

Click here for the TAP file and the source code.

P.S. Assembler functions and loops have been modified to not require any manual adjustment - just change the #define; and also: I have switched to SDCC compiler for better C syntax support :-)