logo
 1
 2
 3
 4
 5
 6
 7
 8
 9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
74
75
76
77
78
79
80
81
82
83
84
85
86
87
88
89
90
91
92
93
94
95
96
97

//! Text renderer.
//!
//! For more complex text rendering cases that are not covered by the [`mono_font`] module, the
//! `TextRenderer` trait can be implemented by external text renderers.
//!
//! Implementations of this trait can be found in the [bdf] and [eg-seven-segment] repositories,
//! which may be useful as a reference of other implementations.
//!
//! [`mono_font`]: ../../mono_font/index.html
//! [bdf]: https://github.com/embedded-graphics/bdf
//! [eg-seven-segment]: https://github.com/embedded-graphics/eg-seven-segment

use crate::{
    draw_target::DrawTarget, geometry::Point, pixelcolor::PixelColor, primitives::Rectangle,
    text::Baseline,
};

mod character_style;

pub use character_style::CharacterStyle;

/// Text renderer.
///
/// The `TextRenderer` trait is used to integrate text renderers into embedded-graphics. Users should
/// not call it directly and instead use the functions provided by the `Text` type.
pub trait TextRenderer {
    /// Color type.
    type Color: PixelColor;

    /// Draws a string.
    ///
    /// The method returns the start position of the next character to allow chaining of multiple
    /// draw calls.
    ///
    /// # Implementation notes
    ///
    /// This method must not interpret any control characters and only render a single line of text.
    /// Any control character in the `text` should be handled the same way as any other character
    /// that isn't included in the font.
    fn draw_string<D>(
        &self,
        text: &str,
        position: Point,
        baseline: Baseline,
        target: &mut D,
    ) -> Result<Point, D::Error>
    where
        D: DrawTarget<Color = Self::Color>;

    /// Draws whitespace of the given width.
    ///
    /// The method returns the start position of the next character to allow chaining of multiple
    /// draw calls.
    fn draw_whitespace<D>(
        &self,
        width: u32,
        position: Point,
        baseline: Baseline,
        target: &mut D,
    ) -> Result<Point, D::Error>
    where
        D: DrawTarget<Color = Self::Color>;

    /// Returns the text metrics for a string.
    ///
    /// # Implementation notes
    ///
    /// The returned bounding box must be independent of the text color. This is different to the
    /// `Dimensions` trait, which should return a zero sized bounding box for completely transparent
    /// drawables. But this behavior would make it impossible to correctly layout text which
    /// contains a mixture of transparent and non transparent words.
    ///
    /// This method must not interpret any control characters and only render a single line of text.
    /// Any control character in the `text` should be handled the same way as any other character
    /// that isn't included in the font.
    fn measure_string(&self, text: &str, position: Point, baseline: Baseline) -> TextMetrics;

    /// Returns the default line height.
    ///
    /// The line height is defined as the vertical distance between the baseline of two adjacent
    /// lines in pixels.
    fn line_height(&self) -> u32;
}

/// Text metrics.
///
/// See [`TextRenderer::measure_string`] for more information.
///
/// [`TextRenderer::measure_string`]: trait.TextRenderer.html#tymethod.measure_string
#[derive(Debug, Copy, Clone, Ord, PartialOrd, Eq, PartialEq, Hash)]
pub struct TextMetrics {
    /// Bounding box.
    pub bounding_box: Rectangle,

    /// The position of the next text.
    pub next_position: Point,
}