Enforce matching dimensions between render context and pixmap when rasterizing

Cargo.lock

diff --git a/Cargo.lock b/Cargo.lock
index ef8dd41..36b2502 100644
--- a/Cargo.lock
+++ b/Cargo.lock
@@ -3744,6 +3744,7 @@
 dependencies = [
  "bytemuck",
  "crossbeam-channel",
+ "log",
  "ordered-channel",
  "rayon",
  "smallvec",

sparse_strips/vello_cpu/Cargo.toml

diff --git a/sparse_strips/vello_cpu/Cargo.toml b/sparse_strips/vello_cpu/Cargo.toml
index f447ac7..d8682df 100644
--- a/sparse_strips/vello_cpu/Cargo.toml
+++ b/sparse_strips/vello_cpu/Cargo.toml
@@ -24,6 +24,7 @@
 rayon = { workspace = true, optional = true }
 smallvec = { workspace = true, optional = true }
 thread_local = { workspace = true, optional = true }
+log = { workspace = true }
 
 
 [features]

sparse_strips/vello_cpu/src/render.rs

diff --git a/sparse_strips/vello_cpu/src/render.rs b/sparse_strips/vello_cpu/src/render.rs
index 115b744..19553be 100644
--- a/sparse_strips/vello_cpu/src/render.rs
+++ b/sparse_strips/vello_cpu/src/render.rs
@@ -15,6 +15,7 @@
 use alloc::sync::Arc;
 use alloc::vec;
 use alloc::vec::Vec;
+use log::warn;
 use vello_common::blurred_rounded_rect::BlurredRoundedRectangle;
 use vello_common::encode::{EncodeExt, EncodedPaint};
 use vello_common::fearless_simd::Level;
@@ -448,9 +449,19 @@
     }
 
     /// Render the current context into a pixmap.
+    /// 
+    /// Note that the pixmap needs to have the same dimensions as the render context.
     pub fn render_to_pixmap(&self, pixmap: &mut Pixmap) {
         let width = pixmap.width();
         let height = pixmap.height();
+        
+        if width != self.width || height != self.height {
+            warn!("cannot render a pixmap with the dimensions {width}x{height} into \
+            a render context with the dimensions {}x{}", self.width, self.height);
+            
+            return;
+        }
+        
         self.render_to_buffer(
             pixmap.data_as_u8_slice_mut(),
             width,
@@ -945,6 +956,7 @@
 mod tests {
     use crate::RenderContext;
     use vello_common::kurbo::{Rect, Shape};
+    use vello_common::pixmap::Pixmap;
     use vello_common::tile::Tile;
 
     #[test]
@@ -981,4 +993,17 @@
         ctx.flush();
         ctx.render_to_pixmap(&mut pixmap);
     }
+    
+    #[test]
+    fn mismatched_dimensions() {
+        let mut ctx = RenderContext::new(20, 15);
+        let mut pixmap = Pixmap::new(20, 20);
+        let rect = Rect::new(0.0, 0.0, 20.0, 20.0);
+
+        ctx.push_layer(Some(&rect.to_path(0.1)), None, None, None);
+        ctx.pop_layer();
+
+        ctx.flush();
+        ctx.render_to_pixmap(&mut pixmap);
+    }
 }