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fix(viewport): clip non-rectangular paper viewports to their boundary shape

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Paper content viewports with a circle / spline / ellipse clip boundary
drew their model content to the full bounding rectangle instead of the
shape. Each paper content viewport is its own render into its own screen
rectangle, so clipping is done per viewport: the boundary polygon is
projected into that viewport's render-target NDC (paper shape mapped
through the same visible-sub-rect crop as the content, so it stays fixed
to the viewport frame) and stamped into the stencil buffer with an
even-odd Invert, which marks the interior of any shape, convex or not,
without triangulation. Every content pass then draws only where the
stencil is set, so hatch, wire, mesh, 3DFACE, text, image, wipeout and
selection are all clipped uniformly.

Because Invert turns the cleared 0x00 into 0xFF, clipped content draws
with stencil reference 0xFF (unclipped content keeps reference 0). The
shared depth buffer moves to Depth24PlusStencil8 across every pipeline.

Rectangular viewports keep clipping via their own render rectangle and
XCLIP keeps its existing CPU wire clip; neither needs the stencil path.

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>
This commit is contained in:
Hakan Seven 2026-07-20 10:02:02 +03:00
commit c97c2a8250
6 changed files with 378 additions and 41 deletions
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21
src/scene/view/render.rs
View file

@ -37,6 +37,11 @@ pub struct ViewportData {
/// reused by a different viewport and reset its (index-addressed) caches.
pub(in crate::scene) instance_id: u64,
pub(in crate::scene) wires: Arc<Vec<WireModel>>,
/// This content viewport's non-rectangular clip boundary (paper layouts
/// only), as a polygon already projected into the viewport's render-target
/// NDC. The GPU stamps it into the stencil so content is clipped to the
/// shape. Empty for rectangular viewports, the paper sheet, and Model space.
pub(in crate::scene) clip_boundary_ndc: Arc<Vec<[f32; 2]>>,
/// Live command-preview / interim / grip-drag overlay wires. Kept out of
/// the main `wires` buffer so a drag re-uploads only this small set each
/// frame, never the resident base buffer. Drawn on top in the wire pass.
@ -570,6 +575,7 @@ impl shader::Primitive for Primitive {
} else {
inner.upload_silhouettes(device, &[], vp.view_dir);
}
inner.upload_clip_boundary(device, &vp.clip_boundary_ndc);
inner.compute_wire_scissors(view_rot, eye, clip_size.width, clip_size.height);
inner.compute_wipeout_scissors(view_rot, eye, clip_size.width, clip_size.height);
inner.compute_image_scissors(view_rot, eye, clip_size.width, clip_size.height);
@ -1352,9 +1358,24 @@ impl Scene {
} else {
0x3000_0000_0000_0000 | inst.handle.value()
};
// A paper content viewport with a non-rectangular clip entity gets its
// boundary projected into this render target's NDC (paper shape mapped
// through the same visible-sub-rect crop as the content). Rectangular
// viewports, the paper sheet and Model tiles clip via their own render
// rectangle and need no stencil boundary.
let clip_boundary_ndc = if !inst.paper_sheet
&& inst.tile_idx.is_none()
&& inst.handle != acadrust::Handle::NULL
&& self.current_layout != "Model"
{
Arc::new(self.viewport_clip_boundary_ndc(inst.handle, uo, vo, us, vs))
} else {
Arc::new(vec![])
};
Some(ViewportData {
instance_id,
wires: all_wires,
clip_boundary_ndc,
preview_wires,
face3d_wires,
text_verts,