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//! Canvas renderer for the browser. Uses `plotters-canvas::CanvasBackend`
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//! and the shared `draw_on` dispatch in `crate::draw`, so a chart
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//! rendered into a `<canvas>` looks identical to its SVG twin.
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//!
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//! Only compiles under feature `canvas`, which is enabled by the
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//! `nomisync-frontend` WASM crate.
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use plotters::prelude::*;

            

        

            

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use plotters_canvas::CanvasBackend;

            

        

            

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use wasm_bindgen::JsValue;

            

        

            

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use web_sys::HtmlCanvasElement;

            

        

            

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use crate::draw::draw_on;

            

        

            

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use crate::spec::ChartSpec;

            

        

            

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/// Render `spec` into `canvas` via `plotters-canvas`. Sizes the

            

        

            

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/// backing canvas to `device_pixel_ratio` so the chart stays crisp on

            

        

            

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/// `HiDPI` screens; the caller is expected to set the CSS width/height

            

        

            

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/// to the logical size before calling.

            

        

            

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///

            

        

            

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/// # Errors

            

        

            

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///

            

        

            

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/// Returns `Err(JsValue)` when the canvas element cannot be wrapped

            

        

            

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/// (missing 2D context or the shared drawing dispatch fails).

            

        

            

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pub fn render_canvas(spec: &ChartSpec, canvas: &HtmlCanvasElement) -> Result<(), JsValue> {

            

        

            

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    apply_dpr(canvas)?;

            

        

            

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    let backend = CanvasBackend::with_canvas_object(canvas.clone())

            

        

            

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        .ok_or_else(|| JsValue::from_str("plotters-canvas: failed to get 2D context"))?;

            

        

            

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    let root = backend.into_drawing_area();

            

        

            

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    draw_on(&root, spec).map_err(|e| JsValue::from_str(&format!("draw failed: {e}")))?;

            

        

            

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    root.present()

            

        

            

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        .map_err(|e| JsValue::from_str(&format!("present failed: {e}")))?;

            

        

            

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    Ok(())

            

        

            

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}

            

        

            

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/// Multiply the backing store by the window's device pixel ratio so

            

        

            

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/// strokes and text stay crisp. CSS width/height (the logical size)

            

        

            

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/// must be set by the caller — this function only touches the

            

        

            

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/// `width`/`height` attributes on the canvas element.

            

        

            

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fn apply_dpr(canvas: &HtmlCanvasElement) -> Result<(), JsValue> {

            

        

            

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    let dpr = web_sys::window()

            

        

            

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        .ok_or_else(|| JsValue::from_str("no window"))?

            

        

            

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        .device_pixel_ratio();

            

        

            

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    if dpr <= 0.0 || !dpr.is_finite() {

            

        

            

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        return Ok(());

            

        

            

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    }

            

        

            

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    let logical_w = f64::from(canvas.client_width().max(1));

            

        

            

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    let logical_h = f64::from(canvas.client_height().max(1));

            

        

            

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    let backing_w = (logical_w * dpr).round().max(1.0) as u32;

            

        

            

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    let backing_h = (logical_h * dpr).round().max(1.0) as u32;

            

        

            

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    // Only resize the backing store when the canvas is attached and has

            

        

            

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    // non-zero CSS dimensions. Otherwise leave the author's width/height

            

        

            

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    // attributes untouched.

            

        

            

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    if logical_w > 0.0 && logical_h > 0.0 {

            

        

            

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        canvas.set_width(backing_w);

            

        

            

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        canvas.set_height(backing_h);

            

        

            

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    }

            

        

            

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    Ok(())

            

        

            

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}