Method move_pixels

web/src/canvas.rs:245–291

(
        &mut self,
        x1y1: PixelsXY,
        x2y2: PixelsXY,
        size: SizeInPixels,
    )

    }

    fn move_pixels(
        &mut self,
        x1y1: PixelsXY,
        x2y2: PixelsXY,
        size: SizeInPixels,
    ) -> io::Result<()> {
        // TODO(jmmv): This is much faster to do than reading and putting pixels... but means we
        // cannot use the "_size" parameter to move just a portion of the image.  This is fine
        // for now because this is only used for console scrolling... but highlights that this
        // generic interface may need tweaking.
        //
        // https://stackoverflow.com/questions/8376534/shift-canvas-contents-to-the-left
        debug_assert_eq!(0, x1y1.x);
        debug_assert_eq!(0, x2y2.x);
        debug_assert_eq!(self.size_pixels.width, size.width);
        debug_assert!(x1y1.y >= x2y2.y);
        debug_assert!(x2y2.y >= 0);
        debug_assert!(
            i32::from(x1y1.y) + i32::from(size.height) <= i32::from(self.size_pixels.height)
        );

        let saved = self.context.global_composite_operation().map_err(js_value_to_io_error)?;
        self.context.set_global_composite_operation("copy").map_err(js_value_to_io_error)?;

        self.context
            .draw_image_with_html_canvas_element(
                self.context.canvas().as_ref().expect("Canvas must be present in context"),
                f64::from(x2y2.x - x1y1.x),
                f64::from(x2y2.y - x1y1.y),
            )
            .map_err(js_value_to_io_error)?;

        self.context.set_global_composite_operation(&saved).map_err(js_value_to_io_error)?;

        let delta_y = i32::from(x1y1.y) - i32::from(x2y2.y);
        debug_assert_eq!(x1y1.x, x2y2.x);
        debug_assert!(delta_y >= 0);
        if delta_y > 0 {
            self.context.fill_rect(
                f64::from(x1y1.x),
                f64::from(x2y2.y) + f64::from(size.height),
                f64::from(size.width),
                f64::from(delta_y),
            );
        }
        Ok(())
    }

    fn write_text(&mut self, xy: PixelsXY, text: &str) -> io::Result<()> {
        draw_text(self, self.font, xy, text)