gameframe-scale

Scaling of a finished frame by a whole multiple, for ports and replacement libraries that draw a 320 × 200 or 640 × 480 picture and show it on a modern screen:

• nearest: every pixel becomes a k × k block. The picture stays exactly the original's.
• scale2x: Andrea Mazzoleni's Scale2x (Eric's Pixel Expansion, EPX), which rounds the staircase on diagonal edges and leaves flat areas and straight edges as they are. scale4x is two passes of it.
• crt: nearest, then the last row of every block darkened, for the look of a CRT's scanlines.

nearest and scale2x take any pixel type that can be copied and compared: palette indices (u8), 16-bit pixels (u16) or 32-bit RGBA (u32). crt works on RGBA in a u32, with each 8-bit channel scaled. Scale the frame after it is finished, never the game's own buffers, so the game's drawing stays bit for bit the original's. No dependencies and no unsafe code.

It comes from the POD: Planet of Death (1997) project, whose replacement Glide and DirectDraw libraries show the game's frame scaled this way (replacement libraries).

Use it

[dependencies]
gameframe-scale = { git = "https://github.com/tanepiper/game-frame" }

use gameframe_scale::{crt, nearest, scale2x};

// A 2 x 2 frame of palette indices.
let frame = [1u8, 2, 3, 4];
let big = nearest(&frame, 2, 2, 2);
assert_eq!(big, [1, 1, 2, 2, 1, 1, 2, 2, 3, 3, 4, 4, 3, 3, 4, 4]);

// Scale2x keeps a flat frame flat.
assert!(scale2x(&[7u8; 9], 3, 3).iter().all(|&p| p == 7));

// The CRT look: rows 0 and 2 keep their colour, rows 1 and 3 (the last of each block) are darker.
let rgba = crt(&[0xff_80_40_20u32], 1, 1, 2, 50);
assert_eq!(rgba, [0xff_80_40_20, 0xff_80_40_20, 0xff_40_20_10, 0xff_40_20_10]);

The output is w * k pixels wide, row after row, as the input is w wide.