Make `Image::paint_at` pixel-perfect crisp for SVG images (#7078)

crates/egui/src/context.rs

@@ -3114,6 +3114,8 @@ impl Context {
         ));
         let max_preview_size = vec2(48.0, 32.0);
 
+        let pixels_per_point = self.pixels_per_point();
+
         ui.group(|ui| {
             ScrollArea::vertical()
                 .max_height(300.0)
@@ -3128,15 +3130,16 @@ impl Context {
                         .show(ui, |ui| {
                             for (&texture_id, meta) in textures {
                                 let [w, h] = meta.size;
+                                let point_size = vec2(w as f32, h as f32) / pixels_per_point;
 
-                                let mut size = vec2(w as f32, h as f32);
+                                let mut size = point_size;
                                 size *= (max_preview_size.x / size.x).min(1.0);
                                 size *= (max_preview_size.y / size.y).min(1.0);
                                 ui.image(SizedTexture::new(texture_id, size))
                                     .on_hover_ui(|ui| {
                                         // show larger on hover
                                         let max_size = 0.5 * ui.ctx().screen_rect().size();
-                                        let mut size = vec2(w as f32, h as f32);
+                                        let mut size = point_size;
                                         size *= max_size.x / size.x.max(max_size.x);
                                         size *= max_size.y / size.y.max(max_size.y);
                                         ui.image(SizedTexture::new(texture_id, size));

crates/egui/src/load.rs

@@ -413,6 +413,8 @@ pub trait ImageLoader {
 #[derive(Clone, Copy, Debug, PartialEq, Eq)]
 pub struct SizedTexture {
     pub id: TextureId,
+
+    /// Size in logical ui points.
     pub size: Vec2,
 }
 

crates/egui/src/widgets/image.rs

@@ -1,6 +1,6 @@
 use std::{borrow::Cow, slice::Iter, sync::Arc, time::Duration};
 
-use emath::{Align, Float as _, Rot2};
+use emath::{Align, Float as _, GuiRounding as _, NumExt as _, Rot2};
 use epaint::{
     text::{LayoutJob, TextFormat, TextWrapping},
     RectShape,
@@ -373,9 +373,23 @@ impl<'a> Image<'a> {
     /// ```
     #[inline]
     pub fn paint_at(&self, ui: &Ui, rect: Rect) {
+        let pixels_per_point = ui.pixels_per_point();
+
+        let rect = rect.round_to_pixels(pixels_per_point);
+
+        // Load exactly the size of the rectangle we are painting to.
+        // This is important for getting crisp SVG:s.
+        let pixel_size = (pixels_per_point * rect.size()).round();
+
+        let texture = self.source(ui.ctx()).clone().load(
+            ui.ctx(),
+            self.texture_options,
+            SizeHint::Size(pixel_size.x as _, pixel_size.y as _),
+        );
+
         paint_texture_load_result(
             ui,
-            &self.load_for_size(ui.ctx(), rect.size()),
+            &texture,
             rect,
             self.show_loading_spinner,
             &self.image_options,
@@ -467,19 +481,24 @@ impl ImageFit {
 impl ImageSize {
     /// Size hint for e.g. rasterizing an svg.
     pub fn hint(&self, available_size: Vec2, pixels_per_point: f32) -> SizeHint {
-        let size = match self.fit {
-            ImageFit::Original { scale } => return SizeHint::Scale(scale.ord()),
+        let point_size = match self.fit {
+            ImageFit::Original { scale } => {
+                return SizeHint::Scale((pixels_per_point * scale).ord())
+            }
             ImageFit::Fraction(fract) => available_size * fract,
             ImageFit::Exact(size) => size,
         };
-        let size = size.min(self.max_size);
-        let size = size * pixels_per_point;
+        let point_size = point_size.at_most(self.max_size);
+
+        let pixel_size = pixels_per_point * point_size;
 
         // `inf` on an axis means "any value"
-        match (size.x.is_finite(), size.y.is_finite()) {
-            (true, true) => SizeHint::Size(size.x.round() as u32, size.y.round() as u32),
-            (true, false) => SizeHint::Width(size.x.round() as u32),
-            (false, true) => SizeHint::Height(size.y.round() as u32),
+        match (pixel_size.x.is_finite(), pixel_size.y.is_finite()) {
+            (true, true) => {
+                SizeHint::Size(pixel_size.x.round() as u32, pixel_size.y.round() as u32)
+            }
+            (true, false) => SizeHint::Width(pixel_size.x.round() as u32),
+            (false, true) => SizeHint::Height(pixel_size.y.round() as u32),
             (false, false) => SizeHint::Scale(pixels_per_point.ord()),
         }
     }