Embedded graphics crate

We'll be starting our graphics journey using the embedded-graphics crate. This crate provides the functionality for drawing basic shapes and text.

Let's start by putting a "Hello, World!" text on the screen.

First, import the necessary types:

#![allow(unused)]
fn main() {
use embedded_graphics::{
    mono_font::{ascii::FONT_10X20, MonoTextStyle},
    text::Text,
};
}

Define the character style:

#![allow(unused)]
fn main() {
let character_style = MonoTextStyle::new(&FONT_10X20, Rgb565::BLACK);
}

And finally, draw the text:

#![allow(unused)]
fn main() {
Text::new(
    "Hello, World!",
    Point::new(90, DISPLAY_SIZE_H as i32 / 2),
    character_style,
)
.draw(&mut display)
.expect("could not draw text");
}

Exercise

Make the text continuously scroll down, wrapping back to the top of the screen.

Hint: check the text.position variable.

Solution

#![allow(unused)]
fn main() {
let character_style = MonoTextStyle::new(&FONT_10X20, Rgb565::BLACK);

// 1. Make text a mutable variable, removing the call to draw().
let mut text = Text::new("Hello, World!", Point::new(90, 0), character_style);

// 2. Create a variable for storing the y position.
let mut y = 0;

loop {
    // 3. Clear the display every time, otherwise
    // the the text will just smudge on the screen.
    display.clear(Rgb565::WHITE).ok();

    // 4. Update text position and draw.
    text.position.y = y;
    text.draw(&mut display).ok();

    // 5. Handle y increment and wrapping.
    // y is at the baseline of the text, so add
    // the text height to make sure we scroll all the way.
    if y == DISPLAY_SIZE_H as i32 + 20 {
        y = 0;
    } else {
        y += 1;
    }

    delay.delay_millis(10);
}
}

💡 Note the use of .ok() in the example below.

Rust compiler will warn us if we ignore the returned Result value, even though sometimes we really don't care if the operation failed.

However, the compiler does not warn about unused Option, so we can use the .ok() method to convert the Result to Option and throw the value away.

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Embedded graphics crate

Exercise