md-gpu-demo

md-gpu-demo is a demoscene-oriented showcase built on top of md-framebuffer-template. It demonstrates what can be done when a SidecarTridge Multi-device cartridge, also known as SidecarT, works together with an Atari ST, STE, Mega ST, or Mega STE.

The repository is not just a static framebuffer sample. It is a small intro/demo playground where the RP2040 in the SidecarT renders effects into a 320x200 chunky framebuffer, while the Atari side receives tear-free 50 Hz updates, keyboard input, palette changes, and YM audio.

What It Shows

The demo set focuses on classic Atari and demoscene building blocks:

• Animated boot menu with a rotozooming SidecarTridge backdrop, palette beating, keyboard navigation, and timing readouts.
• Uridium-style parallax with layered starfields, metal grids, transparent scrolling surfaces, and a controllable ship.
• Filled 3D vector object using fixed-point rotation, projection, backface culling, triangle filling, and shaded Atari ST palettes.
• Multi-sprite stress demo adapted from a Pico VGA demo, showing many animated sprites, transparent blits, and frame-budget tracking.
• Cojorotozoom intro effect with fixed-point rotozoom, bitmap scroll-text, palette ramps, transparent texture sampling, and sprite overlays.

The point is to explore the overlap between the SidecarT's RP2040 compute budget and the visual style of ST-era intros: rotozoomers, scrollers, sprite swarms, parallax, palette tricks, and vector objects running on real Atari hardware.

Relationship To md-framebuffer-template

This repo is based on md-framebuffer-template. For implementation details, build instructions, and the underlying framebuffer framework, use that project as the reference.

Platform

Supported Atari targets:

• Atari ST
• Atari STE
• Atari Mega ST
• Atari Mega STE

Hardware: SidecarTridge Multi-device / SidecarT.

Controls

From the menu:

• Up / Down: move the menu selection
• Return: launch the selected demo
• 1 / 2 / 3 / 4: launch a demo directly
• D: toggle the DRAW/C2P timing readout
• Esc: exit back to GEM

Inside a demo:

• Esc: return to the menu
• D: toggle timing readouts

Some demos use additional cursor-key controls, such as the parallax ship demo's vertical movement.

Returning To Booster

Booster is the SidecarT configurator app used to install, update, and switch microfirmware apps. There are two ways back to it:

• Hold the cartridge SELECT button while powering on / resetting the Atari. This is a hardware escape hatch: it jumps straight to Booster before this app's configuration or emulation runs, so you can always reach the configurator even if the app's settings are wrong or it misbehaves.
• Reflash / power-cycle normally once Booster has been told to load a different app.

Pressing Esc only exits the running demo back to GEM (the Atari desktop); it does not return to Booster.

License

GPL v3.0. See LICENSE.