Model renders (screenshot with source model, ui.render) show the section the window shows: the CPU renderer drew the cut face on the far walls at their own depth in a plain grey hatch, so the inside of the body, its edges and the grid showed through it and the cut barely read as a section, it had no outline, perspective views cut along a curve, and an open Section Analysis dialog's preview (or a sketch's Slice) was ignored. The cut face now writes the section plane's depth where it is the visible surface (the CPU counterpart of the viewport's stencil cap), takes the viewport's cap tint and hatch, the cut outline is drawn (section_segments moved from the UI to engine::view and shared), world positions and lines are clipped perspective-correctly, and ui.render in the app uses the viewport's section plane

crates/render/src/lib.rs

@@ -8,4 +8,4 @@ mod camera;
 mod raster;
 
 pub use camera::{Camera, CameraAnim, Mat4, Quat, StandardView, UpAxis, ease_in_out};
-pub use raster::{Canvas, Rgb, Scene, SceneLine, SceneMesh, png, render, render_png, render_transparent};
+pub use raster::{Canvas, Rgb, SECTION_CAP, Scene, SceneLine, SceneMesh, png, render, render_png, render_transparent};