Trait Canvas

Source

pub trait Canvas {
    type Pixel: Pixel;

    // Required methods
    fn dimensions(&self) -> (u32, u32);
    fn get_pixel(&self, x: u32, y: u32) -> Self::Pixel;
    fn draw_pixel(&mut self, x: u32, y: u32, color: Self::Pixel);

    // Provided methods
    fn width(&self) -> u32 { ... }
    fn height(&self) -> u32 { ... }
}

Expand description

A surface for drawing on - many drawing functions in this library are generic over a Canvas to allow the user to configure e.g. whether to use blending.

All instances of GenericImage implement Canvas, with the behaviour of draw_pixel being equivalent to calling set_pixel with the same arguments.

See Blend for another example implementation of this trait - its implementation of draw_pixel alpha-blends the input value with the pixel’s current value.

§Examples

use image::{Pixel, Rgba, RgbaImage};
use imageproc::drawing::{Canvas, Blend};

// A trivial function which draws on a Canvas
fn write_a_pixel<C: Canvas>(canvas: &mut C, c: C::Pixel) {
    canvas.draw_pixel(0, 0, c);
}

// Background color
let solid_blue = Rgba([0u8, 0u8, 255u8, 255u8]);

// Drawing color
let translucent_red = Rgba([255u8, 0u8, 0u8, 127u8]);

// Blended combination of background and drawing colors
let mut alpha_blended = solid_blue;
alpha_blended.blend(&translucent_red);

// The implementation of Canvas for GenericImage overwrites existing pixels
let mut image = RgbaImage::from_pixel(1, 1, solid_blue);
write_a_pixel(&mut image, translucent_red);
assert_eq!(*image.get_pixel(0, 0), translucent_red);

// This behaviour can be customised by using a different Canvas type
let mut image = Blend(RgbaImage::from_pixel(1, 1, solid_blue));
write_a_pixel(&mut image, translucent_red);
assert_eq!(*image.0.get_pixel(0, 0), alpha_blended);