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web: Support glyphs larger than 1024x1024 in canvas font renderer #22697

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web: Support glyphs larger than 1024x1024 in canvas font renderer #22697

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33 changes: 27 additions & 6 deletions web/src/ui/font_renderer.rs
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Original file line number Diff line number Diff line change
Expand Up @@ -14,6 +14,7 @@ use web_sys::OffscreenCanvasRenderingContext2d;
pub struct CanvasFontRenderer {
canvas: OffscreenCanvas,
ctx: OffscreenCanvasRenderingContext2d,
font_str: String,
ascent: f64,
descent: f64,
}
Expand All @@ -30,17 +31,16 @@ impl CanvasFontRenderer {
return Err(JsValue::from_str("OffscreenCanvas unsupported"));
}

let canvas = OffscreenCanvas::new(1024, 1024)?;
let canvas = OffscreenCanvas::new(1, 1)?;

let ctx = canvas.get_context("2d")?.expect("2d context");
let ctx = ctx
.dyn_into::<OffscreenCanvasRenderingContext2d>()
.map_err(|err| JsValue::from_str(&format!("Not a 2d context: {err:?}")))?;

ctx.set_fill_style_str("white");
let font_str = Self::to_font_str(italic, bold, Self::SIZE_PX, font_family);
tracing::debug!("Using the following font string: {font_str}");
ctx.set_font(&font_str);
Self::apply_style(&ctx, &font_str);

let measurement = ctx.measure_text("Myjg")?;
let ascent = measurement.font_bounding_box_ascent();
Expand All @@ -49,6 +49,7 @@ impl CanvasFontRenderer {
Ok(Self {
canvas,
ctx,
font_str,
ascent,
descent,
})
Expand All @@ -75,12 +76,35 @@ impl CanvasFontRenderer {
format!("{italic}{bold}{size}px {font_family}")
}

fn apply_style(ctx: &OffscreenCanvasRenderingContext2d, font_str: &str) {
ctx.set_fill_style_str("white");
ctx.set_font(font_str);
}

fn calculate_width(&self, text: &str) -> Result<f64, JsValue> {
Ok(self.ctx.measure_text(text)?.width())
}

fn ensure_canvas_large_enough(&self, width: f64, height: f64) {
let width = width.ceil() as u32;
let height = height.ceil() as u32;
if self.canvas.width() < width || self.canvas.height() < height {
self.canvas.set_width(width);
self.canvas.set_height(height);

// After changing canvas size, we need to reapply the style.
// Somehow, when canvas size is too small for the text, the
// text is rendered smaller, but its reported metrics are correct.
Self::apply_style(&self.ctx, &self.font_str);
}
}

fn render_glyph_internal(&self, character: char) -> Result<Glyph, JsValue> {
let text = &character.to_string();
let width = self.calculate_width(text)?;
let height = self.ascent + self.descent;

self.ensure_canvas_large_enough(width, height);

self.ctx.clear_rect(
0.0,
Expand All @@ -90,9 +114,6 @@ impl CanvasFontRenderer {
);
self.ctx.fill_text(text, 0.0, self.ascent)?;

let width = self.calculate_width(text)?;
let height = self.ascent + self.descent;

let image_data = self.ctx.get_image_data(0.0, 0.0, width, height)?;
let width = image_data.width();
let height = image_data.height();
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