Wireframe

since 0.1.0 or earlier Shading and materials

Open the live demo · Read the source · View on GitHub

RenderSettings.wireframe asks the renderer to draw the scene's triangles as lines instead of filled surfaces. It is a polygon mode, and only one of the three backends this engine draws through actually has one: Impeller. WebGL2 has no glPolygonMode, and neither does the software rasteriser this page's own test runs on.

That refusal is not silent. FrameResult.wireframeDeclined is true exactly when a frame asked for wireframe and could not be given it, so a caller can tell "nothing drew" apart from "the device cannot do this."

Step 1: Something with edges worth seeing #

A torus shows its wireframe better than a sphere does: the tube reveals how the two rings of segments cross each other.

final MeshNode knot = MeshNode(
  DeviceMesh.upload(
    context.device,
    const TorusShape(segments: 32, tubeSegments: 16).build(),
  ),
  Material(name: 'knot', baseColor: Vector4(0.3, 0.65, 0.85, 1.0)),
  name: 'knot',
);
return Scene()
  ..add(knot)
  ..add(
    LightNode(name: 'sun', intensity: 3.0)
      ..setLocalForward(Vector3(-0.4, -0.7, -0.6)),
  );

Step 2: Ask for it #

One field, read every frame.

wireframe: wireframe,

Step 3: What actually happened #

On a device that can draw lines, the knot now looks like a wire model. On the software rasteriser, the knot still comes back solid, and wireframeDeclined says why: the request was heard and could not be met.

// The software rasteriser has no polygon-mode line primitive, so this
// page's own claim on this device is the refusal itself: asking for
// wireframe here still draws the model solid, and the frame says why.
if (wireframe && !frame.wireframeDeclined) {
  throw StateError('this device drew wireframe; the claim below is stale');
}
if (frame.drawCalls < 1) {
  throw StateError('the knot was not drawn');
}

Note. This is the one page in this set that leans on Need.wireframe. A device that lacks it still opens the page, with a note that part of what it describes will not show.