Merge PR #8354: Keep the CPU canvas sharp at 100% zoom

ATTRIBUTION.md

@@ -89,6 +89,7 @@ The other built-in ICC profiles and the generated LUT looks are produced by code
 | `docs/images/photocraft-*.jpg` | PhotoCraft screenshots | PhotoCraft contributors (UI) | Rendered offscreen with the `snapshot` example | MIT OR Apache-2.0 (UI); the artwork in each is public domain, listed below |
 | `docs/images/preferences-apply-*.png` | Preferences before and after adding Apply (no artwork) | PhotoCraft contributors | PhotoCraft control-channel capture and offscreen `snapshot` example | MIT OR Apache-2.0 |
 | `docs/images/gradient-overlay-method-*.png` | Gradient Overlay Method selector, before and after (synthetic gradient) | @oRE-o | Rendered offscreen with the `snapshot` example; no external artwork | MIT OR Apache-2.0 |
+| `docs/images/cpu-pixel-alignment/*.png` | CPU canvas pixel alignment, before and after #8321 | PhotoCraft contributors | Original synthetic noise rendered with the offscreen `snapshot` example; see the adjacent README | MIT OR Apache-2.0, adjacent `LICENSE-MIT` and `LICENSE-APACHE` |
 
 Artwork shown in the screenshots (all public domain, via Wikimedia Commons; details in
 [`docs/images/SOURCES.md`](docs/images/SOURCES.md)):

crates/ui-egui/src/canvas.rs

@@ -1050,14 +1050,52 @@ impl ViewXform {
         let v = app.ui.views.get(app.session.active_index()?)?;
         let (zoom, center) =
             if v.zoom_animating && app.session.prefs().general.animated_zoom { v.display_camera.unwrap_or((v.zoom, v.center)) } else { (v.zoom, v.center) };
-        Some(Self {
-            rect: crate::rulers::content_rect(app, app.last_canvas_rect),
-            zoom: zoom / app.canvas_ppp(),
-            center,
-            flip: app.ui.view.flip_horizontal,
-            rotation: v.rotation,
-            aspect: app.ui.view.display_aspect(),
-        })
+        Some(
+            Self {
+                rect: crate::rulers::content_rect(app, app.last_canvas_rect),
+                zoom: zoom / app.canvas_ppp(),
+                center,
+                flip: app.ui.view.flip_horizontal,
+                rotation: v.rotation,
+                aspect: app.ui.view.display_aspect(),
+            }
+            .pixel_aligned_for(app, app.canvas_ppp()),
+        )
+    }
+
+    fn pixel_aligned_for(self, app: &PhotocraftApp, ppp: f32) -> Self {
+        // Default Crop counter-moves the frame and camera with fractional pointer deltas.
+        // Preserve that continuous mapping so its fixed frame does not wobble during a drag.
+        if crate::crop_mode::moves_image(app) { self } else { self.pixel_aligned(ppp) }
+    }
+
+    /// At integer physical magnifications, texel edges must land on display pixel edges.
+    /// Keep this derived camera shared by images, overlays and input without changing the saved pan.
+    fn pixel_aligned(mut self, ppp: f32) -> Self {
+        if !ppp.is_finite() || ppp <= 0.0 || !self.zoom.is_finite() || self.zoom <= 0.0 || !self.rotation.is_finite() || self.rotation.abs() >= 1e-8 {
+            return self;
+        }
+        let scale = vec2(self.zoom_x(), self.zoom) * ppp;
+        if !scale.is_finite()
+            || scale.x.round() < 1.0
+            || scale.y.round() < 1.0
+            || (scale.x - scale.x.round()).abs() > 1e-5
+            || (scale.y - scale.y.round()).abs() > 1e-5
+        {
+            return self;
+        }
+        let origin = self.to_screen(0.0, 0.0);
+        let physical = origin * ppp;
+        if !physical.is_finite() {
+            return self;
+        }
+        let aligned = pos2(physical.x.round(), physical.y.round()) / ppp;
+        let offset = self.unmap_vec((aligned - origin) / self.zoom);
+        let center = [self.center[0] - offset.x, self.center[1] - offset.y];
+        if center.iter().all(|v| v.is_finite()) {
+            self.center = center;
+        }
+        self
     }
 
     fn sincos(self) -> (f32, f32) {
@@ -3476,7 +3514,7 @@ pub fn canvas_view(app: &mut PhotocraftApp, ui: &mut egui::Ui, idx: usize, rect:
     if view.zoom_animating {
         ctx.request_repaint();
     }
-    let xf = ViewXform { zoom: display_view.zoom / ppp, center: display_view.center, ..target_xf };
+    let xf = ViewXform { zoom: display_view.zoom / ppp, center: display_view.center, ..target_xf }.pixel_aligned_for(app, ppp);
     let pixel_grid = app.ui.view.shows(app.ui.view.show.pixel_grid);
     let response = ui.allocate_rect(rect, Sense::click_and_drag());
     let stroke_dismissal = primary && crate::shape_stroke_ui::dismiss_from_canvas(app, &response);
@@ -3530,8 +3568,8 @@ pub fn canvas_view(app: &mut PhotocraftApp, ui: &mut egui::Ui, idx: usize, rect:
                 zoom: view.zoom * k as f32 / ppp,
                 // A size-changing preview grows around the old image center; keep the view's pan.
                 center: [
-                    view.center[0] / k as f32 + (preview_size[0] as f32 - original_size[0] as f32) / 2.0,
-                    view.center[1] / k as f32 + (preview_size[1] as f32 - original_size[1] as f32) / 2.0,
+                    xf.center[0] / k as f32 + (preview_size[0] as f32 - original_size[0] as f32) / 2.0,
+                    xf.center[1] / k as f32 + (preview_size[1] as f32 - original_size[1] as f32) / 2.0,
                 ],
                 rotation: if view.rotation.is_finite() { view.rotation.to_radians() } else { 0.0 },
                 shadow: {
@@ -3554,7 +3592,7 @@ pub fn canvas_view(app: &mut PhotocraftApp, ui: &mut egui::Ui, idx: usize, rect:
                 doc: doc.id.0,
                 doc_size: [doc.size.width, doc.size.height],
                 zoom: point_zoom,
-                center: view.center,
+                center: xf.center,
                 rotation: if view.rotation.is_finite() { view.rotation.to_radians() } else { 0.0 },
                 shadow: {
                     let t = crate::theme::Tokens::get(&ctx);
@@ -4414,7 +4452,7 @@ pub fn canvas_view(app: &mut PhotocraftApp, ui: &mut egui::Ui, idx: usize, rect:
             display_view.center = view.center;
         }
         display_view.rotation = view.rotation;
-        ViewXform { center: display_view.center, rotation: display_view.rotation, ..xf }
+        ViewXform { center: display_view.center, rotation: display_view.rotation, ..xf }.pixel_aligned_for(app, ppp)
     } else {
         xf
     };
@@ -10059,6 +10097,9 @@ mod display_memo_tests;
 #[path = "canvas/blend_viewport_tests.rs"]
 mod blend_viewport_regression;
 
+#[cfg(test)]
+#[path = "canvas/pixel_alignment_tests.rs"]
+mod pixel_alignment_tests;
 #[cfg(test)]
 mod lasso_preview_tests {
     use super::*;

crates/ui-egui/src/canvas/pixel_alignment_tests.rs

@@ -0,0 +1,160 @@
+use super::*;
+
+fn xform(ppp: f32, physical_size: [f32; 2]) -> ViewXform {
+    ViewXform {
+        rect: Rect::from_min_size(pos2(40.0 / ppp, 100.0 / ppp), vec2(physical_size[0] / ppp, physical_size[1] / ppp)),
+        zoom: 1.0 / ppp,
+        center: [1500.0, 1000.0],
+        flip: false,
+        rotation: 0.0,
+        aspect: 1.0,
+    }
+}
+
+fn assert_pixel_edges(xf: ViewXform, ppp: f32) {
+    for [x, y] in [[0.0, 0.0], [1.0, 1.0], [17.0, 29.0], [1500.0, 1000.0]] {
+        let p = xf.to_screen(x, y) * ppp;
+        assert!((p.x - p.x.round()).abs() < 0.001, "x edge: {p:?}, ppp {ppp}");
+        assert!((p.y - p.y.round()).abs() < 0.001, "y edge: {p:?}, ppp {ppp}");
+    }
+}
+
+#[test]
+fn actual_pixels_align_texel_edges_in_odd_viewports_at_every_display_scale() {
+    for ppp in [1.0, 1.25, 1.5, 2.0] {
+        for size in [[523.0, 470.0], [524.0, 471.0], [523.0, 471.0]] {
+            let before = xform(ppp, size);
+            let aligned = before.pixel_aligned(ppp);
+            assert_pixel_edges(aligned, ppp);
+            let delta = (aligned.to_screen(0.0, 0.0) - before.to_screen(0.0, 0.0)) * ppp;
+            assert!(delta.x.abs() <= 0.501 && delta.y.abs() <= 0.501);
+            let again = aligned.pixel_aligned(ppp);
+            assert!((again.to_screen(0.0, 0.0) - aligned.to_screen(0.0, 0.0)).length() < 0.001);
+            let back = aligned.to_doc(aligned.to_screen(123.25, 45.75));
+            assert!((back[0] - 123.25).abs() < 0.001 && (back[1] - 45.75).abs() < 0.001);
+        }
+    }
+}
+
+#[test]
+fn integer_magnification_aligns_flipped_and_aspect_corrected_views() {
+    for flip in [false, true] {
+        let before = ViewXform {
+            rect: Rect::from_min_size(pos2(-20.25, 30.25), vec2(523.0, 471.0)),
+            zoom: 2.0,
+            center: [1500.125, 999.75],
+            flip,
+            aspect: 1.5,
+            ..xform(1.0, [523.0, 471.0])
+        };
+        assert_pixel_edges(before.pixel_aligned(1.0), 1.0);
+    }
+    let even = xform(1.0, [524.0, 470.0]);
+    assert_eq!(even.pixel_aligned(1.0).center, even.center);
+}
+
+#[test]
+fn fractional_zoom_rotation_and_invalid_scales_preserve_the_camera() {
+    let original = xform(1.0, [523.0, 471.0]);
+    for zoom in [0.25, 0.5, 0.75, 1.25, 1.5, 2.5, 0.0, -1.0, f32::NAN, f32::INFINITY] {
+        let xf = ViewXform { zoom, ..original };
+        assert_eq!(xf.pixel_aligned(1.0).center, xf.center);
+    }
+    for rotation in [0.2, 30.0, 90.0, f32::NAN] {
+        let xf = ViewXform { rotation, ..original };
+        assert_eq!(xf.pixel_aligned(1.0).center, xf.center);
+    }
+    for ppp in [0.0, -1.0, f32::NAN, f32::INFINITY] {
+        assert_eq!(original.pixel_aligned(ppp).center, original.center);
+    }
+    let aspect = ViewXform { aspect: 1.2, ..original };
+    assert_eq!(aspect.pixel_aligned(1.0).center, aspect.center);
+}
+
+#[test]
+fn active_transform_uses_the_same_alignment_without_changing_saved_pan() {
+    let mut app = PhotocraftApp::new(photocraft_engine::Session::new(), crate::Services::default());
+    app.run("file.new", serde_json::json!({"width": 3000, "height": 2000})).unwrap();
+    app.sync_views();
+    for ppp in [1.0, 1.25, 1.5, 2.0] {
+        app.ppp = ppp;
+        app.last_canvas_rect = xform(ppp, [523.0, 471.0]).rect;
+        app.ui.views[0].center = [1500.0, 1000.0];
+        app.ui.views[0].zoom = 1.0;
+        let before = app.ui.views[0].center;
+        let active = ViewXform::active(&app).unwrap();
+        assert_pixel_edges(active, ppp);
+        assert_eq!(app.ui.views[0].center, before);
+    }
+}
+
+#[test]
+fn cpu_canvas_paints_its_image_on_physical_pixel_edges() {
+    for ppp in [1.0, 1.25, 2.0] {
+        let mut app = PhotocraftApp::new(photocraft_engine::Session::new(), crate::Services::default());
+        app.run("file.new", serde_json::json!({"width": 64, "height": 64, "background": "white"})).unwrap();
+        app.sync_views();
+        app.ppp = ppp;
+        app.ui.views[0].zoom = 1.0;
+        app.ui.views[0].center = [32.0, 32.0];
+        app.ui.views[0].fit_pending = false;
+        app.ui.views[0].doc_size = [64, 64];
+        let ctx = egui::Context::default();
+        ctx.set_pixels_per_point(ppp);
+        let tex = ensure_texture(&mut app, &ctx, 0, None).unwrap().0;
+        let view = app.ui.views[0].clone();
+        let saved_center = view.center;
+        let mut out = ctx.run_ui(egui::RawInput { screen_rect: Some(Rect::from_min_size(Pos2::ZERO, vec2(900.0, 600.0))), ..Default::default() }, |ui| {
+            canvas_view(&mut app, ui, 0, xform(ppp, [523.0, 471.0]).rect, view.clone(), false);
+        });
+        out.textures_delta.clear();
+        let mesh = out
+            .shapes
+            .iter()
+            .find_map(|s| match &s.shape {
+                egui::Shape::Mesh(mesh) if mesh.texture_id == tex => Some(mesh),
+                _ => None,
+            })
+            .expect("CPU document image quad");
+        assert_eq!(mesh.vertices.len(), 4);
+        for vertex in &mesh.vertices {
+            let p = vertex.pos * ppp;
+            assert!((p.x - p.x.round()).abs() < 0.001 && (p.y - p.y.round()).abs() < 0.001, "ppp {ppp}: {p:?}");
+        }
+        assert_eq!(app.ui.views[0].center, saved_center);
+    }
+}
+
+#[test]
+fn crop_image_movement_keeps_its_continuous_camera_mapping() {
+    let mut app = PhotocraftApp::new(photocraft_engine::Session::new(), crate::Services::default());
+    app.ui.tool = Tool::Crop;
+    let xf = xform(1.0, [523.0, 471.0]);
+    assert_eq!(xf.pixel_aligned_for(&app, 1.0).center, xf.center);
+    app.ui.tool_options.crop_shield.classic_mode = true;
+    assert_pixel_edges(xf.pixel_aligned_for(&app, 1.0), 1.0);
+}
+
+#[test]
+fn animated_active_transform_aligns_the_display_camera_and_preserves_target_pan() {
+    let mut app = PhotocraftApp::new(photocraft_engine::Session::new(), crate::Services::default());
+    app.run("file.new", serde_json::json!({"width": 3000, "height": 2000})).unwrap();
+    app.run("prefs.set", serde_json::json!({"values": {"general.animatedZoom": true}})).unwrap();
+    app.sync_views();
+    for ppp in [1.0, 1.25, 1.5, 2.0] {
+        app.ppp = ppp;
+        app.last_canvas_rect = xform(ppp, [523.0, 471.0]).rect;
+        let v = &mut app.ui.views[0];
+        v.zoom = 3.0;
+        v.center = [1500.0, 1000.0];
+        v.zoom_animating = true;
+        v.display_camera = Some((1.0, [1490.25, 990.75]));
+        let active = ViewXform::active(&app).unwrap();
+        assert_eq!(active.zoom, 1.0 / ppp);
+        assert_pixel_edges(active, ppp);
+        assert!((active.center[0] - 1490.25).abs() <= 0.501);
+        assert!((active.center[1] - 990.75).abs() <= 0.501);
+        assert_eq!(app.ui.views[0].center, [1500.0, 1000.0]);
+        assert_eq!(app.ui.views[0].display_camera, Some((1.0, [1490.25, 990.75])));
+    }
+}

crates/ui-egui/src/zoom_tool.rs

@@ -157,6 +157,14 @@ mod tests {
         ViewXform::active(h.state()).unwrap()
     }
 
+    // Pixel alignment derives a presentation camera within half a display pixel of the
+    // stored target; interrupting an animation must keep that same target and its zoom.
+    fn assert_camera_center(h: &Harness<'static, PhotocraftApp>, target: &View) {
+        let xf = view_xf(h);
+        let delta = (xf.to_screen(target.center[0], target.center[1]) - xf.rect.center()) * h.ctx.pixels_per_point();
+        assert!(delta.x.abs() <= 0.501 && delta.y.abs() <= 0.501, "camera differs by {delta:?} display pixels");
+    }
+
     fn press(h: &mut Harness<'static, PhotocraftApp>, p: Pos2, pressed: bool) {
         h.event(Event::PointerButton { pos: p, button: PointerButton::Primary, pressed, modifiers: Default::default() });
         h.step();
@@ -391,7 +399,7 @@ mod tests {
             let target = &h.state().ui.views[0];
             assert!(!target.zoom_animating, "{command}");
             assert_eq!(view_xf(&h).zoom, target.zoom);
-            assert_eq!(view_xf(&h).center, target.center);
+            assert_camera_center(&h, target);
         }
     }
 
@@ -424,7 +432,7 @@ mod tests {
             h.step();
             let target = &h.state().ui.views[0];
             assert_eq!(view_xf(&h).zoom, target.zoom, "gesture {gesture}");
-            assert_eq!(view_xf(&h).center, target.center, "gesture {gesture}");
+            assert_camera_center(&h, target);
         }
     }
 

docs/images/cpu-pixel-alignment/LICENSE-APACHE

@@ -0,0 +1,177 @@
+
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+
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+      and charge a fee for, acceptance of support, warranty, indemnity,
+      or other liability obligations and/or rights consistent with this
+      License. However, in accepting such obligations, You may act only
+      on Your own behalf and on Your sole responsibility, not on behalf
+      of any other Contributor, and only if You agree to indemnify,
+      defend, and hold each Contributor harmless for any liability
+      incurred by, or claims asserted against, such Contributor by reason
+      of your accepting any such warranty or additional liability.
+
+   END OF TERMS AND CONDITIONS

docs/images/cpu-pixel-alignment/LICENSE-MIT

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+MIT License
+
+Copyright (c) 2026 ArtCraft Team and the PhotoCraft contributors
+
+Permission is hereby granted, free of charge, to any person obtaining a copy
+of this software and associated documentation files (the "Software"), to deal
+in the Software without restriction, including without limitation the rights
+to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
+copies of the Software, and to permit persons to whom the Software is
+furnished to do so, subject to the following conditions:
+
+The above copyright notice and this permission notice shall be included in all
+copies or substantial portions of the Software.
+
+THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
+IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
+FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
+AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
+LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
+OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE
+SOFTWARE.

docs/images/cpu-pixel-alignment/README.md

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+# CPU canvas pixel alignment (#8321)
+
+Original 200 × 200 pixel crops at screen coordinates (200, 250)–(400, 450) from 900 × 600 offscreen renders at display scale 1. The scene is a white 1024 × 768 RGB document with 60% monochromatic Add Noise, viewed at Actual Pixels through the CPU canvas (`--safe-gpu`). No external artwork is used.
+
+`before.png` shows the half-pixel horizontal offset. `after.png` shows the aligned canvas and is byte-for-byte equal to the GPU canvas crop. Their grayscale standard deviations are 17.4105 and 24.6821 respectively. The 901-pixel-wide control stays sharp.
+
+The source document fits the offscreen WARP adapter texture limit, so reduced-texture sampling does not mask the pixel-alignment comparison. These captures are original PhotoCraft assets, licensed MIT OR Apache-2.0 (the license files are alongside them).
+
+Default Crop keeps its continuous camera positioning so the crop frame stays fixed during fractional pointer drags. Normal canvas views and Classic Crop use pixel alignment at integral physical magnifications.