The Magical Number 16

Published on 2017-10-27 in µGame.

I’m trying to budget the memory of this thing, for graphics is known to take a lot of it. There is a number of tricks I plan to use to save memory in order to fit into the 32kB available, together with the CircuitPython runtime.

• Frozen modules. All the code libraries, and all the data that doesn’t change (fonts, pre-defined palettes, pre-defined graphic, pre-defined sounds) are going to be byte-compiled and included in the firmware, to be executed directly from the chip’s flash memory.

• Tiles. The basic unit of graphic in the game will be a 16x16 square with 16 colors, called a tile.

• Banks. Tiles will be stored in banks, 16 tiles in a bank. All tiles in a single bank share a palette.

• Palettes. The 16-color palettes will be switchable, so that you will be able to reuse a lot of graphics by simply changing the colors. One of the colors (pure magenta) will be always treated as transparent.

• Layers. A layer is a map of 16x16 tiles from a single bank with a single palette. It has x, y and z offsets, which control where on the screen it is being displayed and what it covers or is covered by it.

• Fonts. Fonts are similar to banks, except they use 8x8 images with 4 colors. They can only be displayed on a special text layer, which is on top of everything else and can’t be scrolled.

• Sprites. Those are like 1x1 layers with just one tile on them. They have x, y and z position, an assigned bank and palette, and the index of the image from that bank to be displayed.

• Dirty rectangles. Those are the areas of the screen that need to be updated in a given frame. Changing a square in a layer or sprite adds the corresponding area of the screen to the dirty rectangles list. Moving a sprite adds both the old and the new position (merged into one rectangle if they overlap). Moving a layer forces redraw of the entire screen (but there will be a trick for scrolling).

That’s the plan for now, anyways.