Module cyd 

Portable display and touch interfaces for Cheap Yellow Display (CYD) applications.

The Cyd trait represents a ready-to-use device with a display and calibrated touch input. Hardware, browser, and in-memory devices all provide the same Cyd, CydDisplay, CydTouch, and CydFrame interfaces.

Portable CYD abstraction

CydEsp / CydRp / CydWasm / CydMemory
                  │ implement
                  ▼
                 Cyd
          ┌───────┴───────┐
    parts().0         parts().1
    CydDisplay        CydTouch
         │                 │
 frame_mut()          try_read()
         ▼                 ▼
    CydFrame          TouchEvent
 borrowed frame       calibrated + oriented

Cyd::parts borrows the display and touch components together. CydDisplay::frame_mut returns a temporary borrowed frame for a display region, while CydTouch::try_read returns already calibrated and oriented events. A full-screen frame is the special case where the borrowed region is the complete display.

Touch-event coordinates and drawing coordinates use the same logical orientation. Do not rotate touch points again.

See CYD in action

Linkage Blaze demonstrates animated clocks, mechanisms, and figures built with Device Envoy’s portable CYD display APIs. Explore the examples in the interactive Linkage Blaze gallery.

Application example

Startup code constructs the appropriate CYD device. Application code can then read calibrated touch input and draw without naming a platform-specific type:

use device_envoy_core::cyd::{
    Cyd, CydDisplay, CydTouch,
    display::{CydFrame, DrawItem},
    touch::TouchEvent,
};
use embedded_graphics::pixelcolor::{Rgb888, RgbColor};

async fn draw_once<C: Cyd>(cyd: &mut C) -> Result<(), C::Error> {
    let (display, touch) = cyd.parts();
    let touch_event = touch.try_read()?;
    let mut frame = display.full_frame_mut();

    frame.write_text("Hello CYD");
    if let Some(TouchEvent::Down { point } | TouchEvent::Move { point }) =
        touch_event
    {
        DrawItem::Circle {
            center: (point.x as f32, point.y as f32),
            pixel_radius: 24.0,
            color: Rgb888::RED,
        }
        .draw(&mut frame);
    }

    frame.flush().await
}

An application would normally call draw_once repeatedly as part of its event or frame loop.

Choose a drawing strategy

The example uses a full-screen buffered frame, the simplest and most flexible option but also the one that requires the most memory. Start with CydDisplay::full_frame_mut when a full-screen buffer is practical. CydDisplay supports four general drawing strategies:

• Full-screen buffering: Use CydDisplay::full_frame_mut to draw the complete display into one buffer before flushing it. This is the simplest and most flexible approach, but it requires one RGB565 value for every screen pixel.
• Regional buffering: Use CydDisplay::frame_mut to draw graphics or text into a smaller rectangular buffer and flush it to any chosen region of the screen. Successive calls can reuse the same storage with different positions, widths, and heights, provided each rectangle fits the buffer’s pixel capacity.
• Tiled drawing: Use CydDisplay::for_each_tile to redraw the scene one small tile at a time when a larger buffer would use too much memory. This requires only one tile-sized buffer.
• Contiguous streaming: Use CydDisplay::fill_contiguous or CydDisplay::fill_contiguous_full to generate or supply row-major RGB565 pixels as the display consumes them. This needs no reusable pixel frame buffer and is useful whenever each pixel can be computed quickly from its screen coordinates, including simple geometric shapes, procedural graphics, and existing bitmap data.

Small heterogeneous scenes can instead be streamed with CydDisplay::draw_items, which also needs no reusable pixel frame buffer. See the CydDisplay documentation for the compact storage table, immediate-drawing capacity rule, and coordinate conventions.

Implementations

• CydEsp runs on ESP32 hardware.
• CydRp runs on Raspberry Pi Pico hardware.
• CydWasm provides interactive browser simulation with the wasm feature.
• CydMemory provides fast, deterministic native desktop tests with the host feature.

Modules

display

Display-only data, asset, and drawing plumbing for the CYD’s cyd device abstraction.

touch

Touch-side support types for the CYD’s cyd device abstraction.

Constants

SCREEN_PIXELS

Total panel pixel count (SCREEN_WIDTH * SCREEN_HEIGHT = 320 * 240 = 76,800).

Traits

Cyd

A ready-to-use CYD device with display and calibrated touch components.

CydDisplay

A CYD display.

CydTouch

A CYD touch source that returns calibrated, oriented touch events in logical display coordinates.