diff --git a/crates/ui-egui/src/about.rs b/crates/ui-egui/src/about.rs
index d0323a999..3fe10eac5 100644
--- a/crates/ui-egui/src/about.rs
+++ b/crates/ui-egui/src/about.rs
@@ -52,7 +52,7 @@ pub fn paint_mark(ui: &egui::Ui, rect: Rect, color: Color32) {
         let mut res = vello_cpu::Resources::new();
         rc.render(&mut pm, &mut res);
         let ci = egui::ColorImage::from_rgba_premultiplied([px as usize, px as usize], pm.data_as_u8_slice());
-        let t = ctx.load_texture("artcraft_mark", ci, egui::TextureOptions::LINEAR);
+        let t = crate::widgets::load_texture(ctx, "artcraft_mark", ci, egui::TextureOptions::LINEAR);
         ctx.data_mut(|d| d.insert_temp(key, t.clone()));
         t
     });
diff --git a/crates/ui-egui/src/canvas.rs b/crates/ui-egui/src/canvas.rs
index 24150ede7..ef5ed0ef4 100644
--- a/crates/ui-egui/src/canvas.rs
+++ b/crates/ui-egui/src/canvas.rs
@@ -587,6 +587,11 @@ fn patch_texture(app: &mut DesignApp, layout: &CanvasLayout, ppp: f64, doc_key:
     let Some(regions) = designcraft_render::damage::damage_with(&old, &new, Some(&app.session.cache)) else { return false };
     let t0 = crate::now_ms();
     let (tw, th) = ((sh.size.0 as f64 * ppp).round() as i64, (sh.size.1 as f64 * ppp).round() as i64);
+    // A texture `upload` sampled down to the GPU limit has other pixels than the view: a region
+    // computed in view pixels would be written outside it. Render it whole instead.
+    if app.canvas.texture.as_ref().is_none_or(|t| t.size() != [tw.max(0) as usize, th.max(0) as usize]) {
+        return false;
+    }
     let k = sh.zoom * ppp;
     let mut px: Option<(i64, i64, i64, i64)> = None;
     for (r, rect) in &regions {
@@ -667,6 +672,7 @@ fn upload(app: &mut DesignApp, ctx: &egui::Context, mut img: designcraft_render:
         designcraft_render::separation_view(&mut img, None, app.ui.ink_limit);
     }
     let ci = egui::ColorImage::from_rgba_premultiplied([img.width as usize, img.height as usize], &img.pixels);
+    let ci = crate::widgets::fit_texture(ci, ctx.input(|i| i.max_texture_side));
     match &mut app.canvas.texture {
         Some(tex) => tex.set(ci, egui::TextureOptions::LINEAR),
         None => app.canvas.texture = Some(ctx.load_texture("canvas", ci, egui::TextureOptions::LINEAR)),
@@ -1336,7 +1342,7 @@ fn draw_inverse_highlight(
             let mut res = vello_cpu::Resources::new();
             rc.render(&mut pm, &mut res);
             let ci = egui::ColorImage::from_rgba_premultiplied([w as usize, h as usize], pm.data_as_u8_slice());
-            let t = ctx.load_texture("inverse_selection", ci, egui::TextureOptions::NEAREST);
+            let t = crate::widgets::load_texture(ctx, "inverse_selection", ci, egui::TextureOptions::NEAREST);
             ctx.data_mut(|d| d.insert_temp(cache_id, (key, t.clone())));
             t
         }
@@ -2238,6 +2244,38 @@ mod tests {
         (s.horizontal_units, s.vertical_units)
     }
 
+    /// A viewport wider than the GPU's largest texture: the canvas texture is sampled down, and an
+    /// edit repaints it whole. A region repainted in view pixels would land in the wrong place,
+    /// or outside the texture (a wgpu validation error). A view that fits is still patched.
+    #[test]
+    fn an_edit_repaints_a_canvas_texture_sampled_down_to_the_gpu_limit_whole() {
+        for (width, sampled_down) in [(1440.0, false), (2600.0, true)] {
+            let mut app = DesignApp::new(designcraft_engine::Session::new(), crate::Services::default());
+            app.run("file.new", json!({})).unwrap();
+            let frame = app.run("frame.create", json!({"rect": [72, 72, 400, 300], "content": "text", "text": "Text"})).unwrap();
+            let mut h = Harness::builder().with_size(vec2(width, 900.0)).build_ui_state(
+                |ui, app: &mut DesignApp| {
+                    let ctx = ui.ctx().clone();
+                    app.logic(&ctx);
+                    app.ui(ui);
+                },
+                app,
+            );
+            h.run_steps(6);
+            let limit = h.ctx.input(|i| i.max_texture_side);
+            let size = h.state().canvas.texture.as_ref().map(|t| t.size()).unwrap();
+            assert!(size[0] <= limit && size[1] <= limit, "{size:?}");
+            let shown = h.state().canvas.shown.unwrap().size;
+            assert_eq!(shown.0 > limit as f32, sampled_down, "view {shown:?}, limit {limit}");
+            let patches = h.state().canvas.patches;
+            // A small edit: one more character in the frame.
+            h.state_mut().run("text.insert", json!({"story": frame["story"], "at": 4, "text": "s"})).unwrap();
+            h.run_steps(6);
+            assert_eq!(h.state().canvas.patches == patches, sampled_down, "width {width}");
+            assert_eq!(h.state().canvas.texture.as_ref().map(|t| t.size()), Some(size));
+        }
+    }
+
     #[test]
     fn selected_merged_owners_paint_the_same_row_and_column_targets() {
         for column in [true, false] {
diff --git a/crates/ui-egui/src/panels/glyphs.rs b/crates/ui-egui/src/panels/glyphs.rs
index 63f02e9ac..61c9cb42d 100644
--- a/crates/ui-egui/src/panels/glyphs.rs
+++ b/crates/ui-egui/src/panels/glyphs.rs
@@ -76,7 +76,11 @@ pub fn show(app: &mut DesignApp, ui: &mut egui::Ui) {
     let bar = scroll.bar_inner_margin + scroll.bar_width + scroll.bar_outer_margin;
     let cols = (((ui.available_width() - bar) / CELL).floor() as u32).max(1);
     let ppp = ui.ctx().pixels_per_point();
-    let cell_px = (CELL * ppp).round() as u32;
+    let cell_px = (CELL * ppp).round().max(1.0) as u32;
+    // The grid is one texture: no more rows than the GPU's largest texture holds (a narrow
+    // panel of a large CJK font ran past it).
+    let max_rows = (ui.ctx().input(|i| i.max_texture_side) as u32 / cell_px).max(1);
+    chars.truncate((max_rows * cols) as usize);
     let ink = t.text_strong;
     let key = egui::Id::new(("glyph_grid", &st.family, &st.style, scope, &q, cols, cell_px, ink.to_array()));
     let tex: egui::TextureHandle = match ui.data(|d| d.get_temp::<egui::TextureHandle>(key)) {
@@ -84,7 +88,7 @@ pub fn show(app: &mut DesignApp, ui: &mut egui::Ui) {
         None => {
             let img = designcraft_render::glyphs::glyph_grid(&db, &st.family, &st.style, &chars, cols, cell_px, ink.to_array());
             let ci = egui::ColorImage::from_rgba_premultiplied([img.width as usize, img.height as usize], &img.pixels);
-            let h = ui.ctx().load_texture("glyph_grid", ci, egui::TextureOptions::LINEAR);
+            let h = crate::widgets::load_texture(ui.ctx(), "glyph_grid", ci, egui::TextureOptions::LINEAR);
             ui.data_mut(|d| d.insert_temp(key, h.clone()));
             h
         }
diff --git a/crates/ui-egui/src/panels/mod.rs b/crates/ui-egui/src/panels/mod.rs
index e728aa94c..c88ae30a3 100644
--- a/crates/ui-egui/src/panels/mod.rs
+++ b/crates/ui-egui/src/panels/mod.rs
@@ -447,7 +447,7 @@ pub fn font_menu_body(app: &mut DesignApp, ui: &mut egui::Ui, menu: &[designcraf
             let tex = tex.unwrap_or_else(|| {
                 let img = designcraft_render::glyphs::text_line(&fonts, f, "Regular", "Sample", (18.0 * ppp) as u32, t.text.to_array());
                 let ci = egui::ColorImage::from_rgba_premultiplied([img.width as usize, img.height as usize], &img.pixels);
-                let h = ui.ctx().load_texture(format!("font_preview_{f}"), ci, egui::TextureOptions::LINEAR);
+                let h = crate::widgets::load_texture(ui.ctx(), format!("font_preview_{f}"), ci, egui::TextureOptions::LINEAR);
                 ui.data_mut(|d| d.insert_temp(key, h.clone()));
                 h
             });
diff --git a/crates/ui-egui/src/panels/pages.rs b/crates/ui-egui/src/panels/pages.rs
index ad8a8ab86..2d6d56da2 100644
--- a/crates/ui-egui/src/panels/pages.rs
+++ b/crates/ui-egui/src/panels/pages.rs
@@ -34,7 +34,7 @@ fn thumb(app: &mut DesignApp, ctx: &egui::Context, abs: usize, h: f32) -> Option
         &designcraft_render::RenderOptions { printing_only: true, ..Default::default() },
     )?;
     let ci = egui::ColorImage::from_rgba_premultiplied([img.width as usize, img.height as usize], &img.pixels);
-    let tex = ctx.load_texture(format!("thumb{abs}"), ci, egui::TextureOptions::LINEAR);
+    let tex = crate::widgets::load_texture(ctx, format!("thumb{abs}"), ci, egui::TextureOptions::LINEAR);
     // Drop thumbnails of older revisions.
     let (uid, rev) = (st.uid, st.revision);
     map.retain(|k, _| !(k.0 == uid && k.1 != rev));
diff --git a/crates/ui-egui/src/widgets.rs b/crates/ui-egui/src/widgets.rs
index af5a7b46c..44316fda4 100644
--- a/crates/ui-egui/src/widgets.rs
+++ b/crates/ui-egui/src/widgets.rs
@@ -717,3 +717,49 @@ mod tests {
         assert_eq!(m.step(), 1.0);
     }
 }
+
+/// `img` made to fit the GPU's largest texture (`max_side` pixels a side), sampled down
+/// (nearest pixel) when it is larger. A texture past the limit panics in the renderer, so every
+/// UI texture goes through this: an oversized image loses resolution, not the document.
+pub fn fit_texture(img: egui::ColorImage, max_side: usize) -> egui::ColorImage {
+    let [w, h] = img.size;
+    let max_side = max_side.max(1);
+    if w <= max_side && h <= max_side {
+        return img;
+    }
+    let k = (max_side as f64 / w.max(h) as f64).min(1.0);
+    let (nw, nh) = (((w as f64 * k).floor() as usize).clamp(1, max_side), ((h as f64 * k).floor() as usize).clamp(1, max_side));
+    let mut pixels = Vec::with_capacity(nw * nh);
+    for y in 0..nh {
+        let sy = (y * h / nh).min(h.saturating_sub(1));
+        for x in 0..nw {
+            let sx = (x * w / nw).min(w.saturating_sub(1));
+            pixels.push(img.pixels.get(sy * w + sx).copied().unwrap_or(Color32::TRANSPARENT));
+        }
+    }
+    egui::ColorImage::new([nw, nh], pixels)
+}
+
+/// [`egui::Context::load_texture`] for an image of any size (see [`fit_texture`]).
+pub fn load_texture(ctx: &egui::Context, name: impl Into<String>, img: egui::ColorImage, options: egui::TextureOptions) -> egui::TextureHandle {
+    let max = ctx.input(|i| i.max_texture_side);
+    ctx.load_texture(name, fit_texture(img, max), options)
+}
+
+#[cfg(test)]
+mod texture_tests {
+    /// The glyph grid that crashed the renderer: 7 columns of 1200 characters at 60 px, 10320 px
+    /// tall against an 8192 px limit.
+    #[test]
+    fn oversized_images_fit_the_texture_limit() {
+        let img = egui::ColorImage::new([420, 10320], vec![egui::Color32::WHITE; 420 * 10320]);
+        let out = super::fit_texture(img, 8192);
+        assert!(out.size[0] <= 8192 && out.size[1] == 8192, "{:?}", out.size);
+        assert_eq!(out.pixels.len(), out.size[0] * out.size[1]);
+        let small = egui::ColorImage::new([10, 10], vec![egui::Color32::RED; 100]);
+        assert_eq!(super::fit_texture(small, 8192).size, [10, 10]);
+        let wide = egui::ColorImage::new([20000, 3], vec![egui::Color32::RED; 60000]);
+        let out = super::fit_texture(wide, 8192);
+        assert!(out.size[0] == 8192 && out.size[1] >= 1);
+    }
+}