Fix panic in the software renderer with clipped text and scale factor

CHANGELOG.md

@@ -7,6 +7,7 @@ All notable changes to this project are documented in this file.
 
  - Fixed compiler panics when some complex expressions are used for the model expression in `for` (#2977)
  - Native style: Fixed support for floating point ranges in Slider.
+ - Fixed panics in the software renderer related to text rendering.
 
 ### Slint Language
 

internal/core/software_renderer.rs

@@ -231,9 +231,12 @@ impl SoftwareRenderer {
         } else {
             (euclid::size2(pixel_stride as _, (buffer.len() / pixel_stride) as _), Brush::default())
         };
+        if size.is_empty() {
+            return Default::default();
+        }
         assert!(
             pixel_stride >= size.width as usize
-                && buffer.len() >= size.height as usize * pixel_stride + size.width as usize - pixel_stride,
+                && buffer.len() >= (size.height as usize * pixel_stride + size.width as usize) - pixel_stride,
             "buffer of size {} with stride {pixel_stride} is too small to handle a window of size {size:?}", buffer.len()
         );
         let buffer_renderer = SceneBuilder::new(
@@ -254,8 +257,11 @@ impl SoftwareRenderer {
                     renderer.compute_dirty_regions(component, *origin);
                 }
 
-                let dirty_region =
-                    (renderer.dirty_region.to_rect().cast() * factor).round_out().cast();
+                let dirty_region = (renderer.dirty_region.to_rect().cast() * factor)
+                    .round_out()
+                    .intersection(&euclid::rect(0., 0., i16::MAX as f32, i16::MAX as f32))
+                    .unwrap_or_default()
+                    .cast();
 
                 let to_draw = self.apply_dirty_region(dirty_region, size);
 
@@ -1367,7 +1373,10 @@ impl<'a, T: ProcessScene> SceneBuilder<'a, T> {
 
                         if let Some(clipped_src) = src_rect.intersection(&physical_clip) {
                             let geometry = clipped_src.translate(offset).round();
-                            let origin = (geometry.origin - offset.round()).cast::<usize>();
+                            if geometry.is_empty() {
+                                continue;
+                            }
+                            let origin = (geometry.origin - offset.round()).round().cast::<usize>();
                             let actual_x = origin.x - src_rect.origin.x as usize;
                             let actual_y = origin.y - src_rect.origin.y as usize;
                             let stride = glyph.width.get() as u16;

tests/screenshots/build.rs

@@ -73,6 +73,20 @@ fn main() -> std::io::Result<()> {
         writeln!(generated_file, "#[path=\"{0}.rs\"] mod r#{0};", module_name)?;
         let source = std::fs::read_to_string(&testcase.absolute_path)?;
 
+        let needle = "SLINT_SCALE_FACTOR=";
+        let scale_factor = if let Some(p) = source.find(needle) {
+            let source = &source[p + needle.len()..];
+            let scale_factor: f32 = source
+                .find(char::is_whitespace)
+                .and_then(|end| source[..end].parse().ok())
+                .unwrap_or_else(|| {
+                    panic!("Cannot parse {needle} for {}", testcase.relative_path.display())
+                });
+            format!("slint::platform::WindowAdapter::window(&*window).dispatch_event(slint::platform::WindowEvent::ScaleFactorChanged {{ scale_factor: {scale_factor}f32 }});")
+        } else {
+            String::new()
+        };
+
         let mut output = std::fs::File::create(
             Path::new(&std::env::var_os("OUT_DIR").unwrap()).join(format!("{}.rs", module_name)),
         )?;
@@ -86,6 +100,7 @@ fn main() -> std::io::Result<()> {
     use crate::testing;
 
     let window = testing::init_swr();
+    {scale_factor}
     window.set_size(slint::PhysicalSize::new(64, 64));
     let screenshot = {reference_path};
 

tests/screenshots/cases/software/basic/text-clipped.slint

@@ -0,0 +1,124 @@
+// Copyright © SixtyFPS GmbH <info@slint.dev>
+// SPDX-License-Identifier: GPL-3.0-only OR LicenseRef-Slint-Royalty-free-1.0 OR LicenseRef-Slint-commercial
+
+// SLINT_SCALE_FACTOR=1.5
+
+export component TestCase inherits Window {
+    width: 64phx;
+    height: 64phx;
+    Rectangle {
+        x: 1.49999997px;
+        y: 1.5px;
+        width: 15.33px;
+        height: 15.33px;
+        clip: true;
+        background: pink;
+        Text {
+            text: "Hello\nWorld";
+            font-size: 9.5px;
+            color: black;
+            horizontal-alignment: center;
+            vertical-alignment: center;
+        }
+    }
+
+    Rectangle {
+        x: 17.333px;
+        y: 1.5px;
+        width: 15.33px;
+        height: 24.18px;
+        clip: true;
+        background: orange;
+        opacity: 0.9;
+        Text {
+            height: 133%;
+            width: 121%;
+            text: "Three\nLines\nText";
+            font-size: 9px;
+            color: blue;
+            font-weight: 600;
+            font-italic: true;
+            horizontal-alignment: right;
+        }
+    }
+
+    Rectangle {
+        x: 33.5px;
+        y: 1.1px;
+        width: 28.33px;
+        height: 25.9px;
+        clip: true;
+        background: lightblue;
+        property <percent> dd;
+        Text {
+            height: 100%; width: 100%;
+            text: "Word wrap and right Align";
+            wrap: word-wrap;
+            horizontal-alignment: right;
+            vertical-alignment: bottom;
+            font-size: 9.1px;
+            color: violet;
+        }
+    }
+
+    Text {
+        height: 99%; width: 99%;
+        y: 2.499997px;
+        x: -20.49997px;
+        text: "Some long text bottom-right-aligned";
+        wrap: word-wrap;
+        overflow: elide;
+        horizontal-alignment: right;
+        vertical-alignment: bottom;
+        font-size: 9px;
+        color: violet;
+    }
+
+
+    Text {
+        height: 99%; width: 99%;
+        y: 2.499997px;
+        x: -20.49997px;
+        text: "Some long text bottom-right-aligned";
+        wrap: word-wrap;
+        overflow: elide;
+        horizontal-alignment: right;
+        vertical-alignment: bottom;
+        font-size: 9px;
+        color: violet;
+    }
+
+    Rectangle {
+        background: #8234;
+        x: 38.788px;
+        y: 30.123px;
+        width: 30px;
+        height: 30px;
+        clip: true;
+        Text {
+            y: -2.5px;
+            x: -2.5px;
+            width: 110%;
+            height: 110%;
+            property <string> t: "tiny tiny text nobody can see\nhelloooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooo\n this is soooo smallllllllllllllllllll and so tiny"
+                +" \nnobody can read this anyway.";
+            text: t+t+t+t;
+
+            wrap: word-wrap;
+            overflow: elide;
+            horizontal-alignment: left;
+            font-size: 4px;
+            letter-spacing: -1px;
+
+            color: green;
+        }
+    }
+
+    Text {
+        property <float> zero: 0;
+        text: "Zero";
+        x: zero * 5px / zero;
+    }
+
+
+}

tests/screenshots/testing.rs

@@ -230,7 +230,9 @@ pub fn screenshot_render_by_line(
                 euclid::point2(0., 0.),
                 euclid::point2(buffer.width() as f32, buffer.height() as f32),
             )),
-            Some(r) => renderer.mark_dirty_region(DirtyRegion::from_untyped(&r.to_box2d().cast())),
+            Some(r) => renderer.mark_dirty_region(
+                DirtyRegion::from_untyped(&r.to_box2d().cast()) / window.scale_factor(),
+            ),
         }
         renderer.render_by_line(TestingLineBuffer {
             stride: buffer.width() as usize,