Tutorial 114: PBR Materials with PbrEffect and SkinnedPbrEffect

CNA Tutorials  ·  3D Content

PbrEffect and SkinnedPbrEffect implement glTF 2.0’s metallic-roughness material model against the specification’s own reference BRDF: a GGX normal distribution, Smith-Schlick-GGX visibility, and Schlick Fresnel. They are CNAEXT effects with the familiar stock-effect workflow — construct one, set properties, bind it, draw.

They are also unambiguously CNAEXT. Real XNA 4.0 predates the physically-based content pipeline entirely; there is no XNA or FNA equivalent to mirror, so nothing here is an attempt at API fidelity. Tutorial 115 explains what that marker means for your build.

The material surface

Each of the seven texture slots comes as a getter, a raw-pointer setter and an owning setter that keeps the texture alive. The five core slots use the original property names; the two KHR_materials_specular slots carry the EXT suffix.

The metallic-roughness map uses glTF’s own packing — green is roughness, blue is metallic. The occlusion map is read from the red channel, where 1 is fully lit and 0 fully occluded.

The scalar and vector factors multiply into those maps, and work perfectly well on their own when a slot is empty:

Putting it together, a hand-built brushed-metal material:

#include "Microsoft/Xna/Framework/Graphics/PbrEffect.hpp"

using namespace Microsoft::Xna::Framework;
using namespace Microsoft::Xna::Framework::Graphics;

PbrEffect effect(device);

effect.setTextureProperty(&albedo);
effect.setNormalMapProperty(&normal);
effect.setMetallicRoughnessMapProperty(&metalRough);

effect.setMetallicFactorProperty(1.0f);
effect.setRoughnessFactorProperty(0.35f);
effect.setEmissiveFactorProperty(Vector3::Zero);

effect.setWorldProperty(world);
effect.setViewProperty(view);
effect.setProjectionProperty(projection);
effect.EnableDefaultLighting();

Use the SetOwned* variants when the effect should outlive your own reference to the texture — which is exactly what the model importers do, since the textures they decode have no other owner:

effect.SetOwnedNormalMap(std::shared_ptr<Texture2D>(std::move(decodedNormalMap)));

Lit by three directional lights, not an environment

PbrEffect implements IEffectMatrices, IEffectFog and IEffectLights, so its lighting and fog surface is the one you already know from BasicEffect: DirectionalLight0 through DirectionalLight2, setAmbientLightColorProperty(), EnableDefaultLighting(), and the four fog properties.

DirectionalLight& key = effect.getDirectionalLight0Property();
key.setEnabledProperty(true);
key.setDirectionProperty(Vector3::Normalize(Vector3(-0.5f, -1.0f, -0.3f)));
key.setDiffuseColorProperty(Vector3(1.0f, 0.96f, 0.9f));

effect.setAmbientLightColorProperty(Vector3(0.05f, 0.06f, 0.08f));

One divergence from the other stock effects: setLightingEnabledProperty(false) is refused. A physically-based material with no lighting has no defined meaning, so the effect mirrors the same constraint real XNA’s SkinnedEffect already imposes.

SkinnedPbrEffect

SkinnedPbrEffect is the whole material surface above plus SkinnedEffect’s bone API — identical names, identical limits:

Which means an AnimationPlayer drives it exactly as it drives a SkinnedEffect:

pbrSkinned.SetBoneTransforms(player.GetSkinTransforms());

See Tutorial 112 for the player, and Tutorial 57 for the bone limits in detail.

How the importer decides

You will usually not construct these effects yourself — the glTF importer picks one per mesh part. In alpha.1 the choice follows the material model, not the presence of a particular texture.

PBR takes priority over the legacy dual-texture approximation. Vertex colour multiplies the PBR base colour in both rigid and skinned layouts; it no longer changes the selected material model.

Once the importer has chosen, the maps and factors are wired in for you, including KHR_materials_emissive_strength, whose multiplier is folded into the emissive factor before the emissive texture is applied. To adjust an imported material at runtime, cast and set:

for (ModelMesh* mesh : model->getMeshesProperty()) {
    for (ModelMeshPart* part : mesh->getMeshPartsProperty()) {
        if (auto* pbr = dynamic_cast<PbrEffect*>(part->getEffectProperty())) {
            pbr->setRoughnessFactorProperty(0.8f);   // scuff the whole surface
        }
    }
}

Factor-only and material state

The same rule covers a primitive with no material object: glTF defines that case as its default metallic-roughness material, so CNA creates the corresponding PBR effect rather than silently substituting a different lighting model.

Renderer coverage

Sixteen implementation families consume the universal alpha.1 PBR draw parameters:

These are implementation families, not public identity counts: EasyGL alone serves five renderer identities. A renderer outside the table is not evidence of equivalent PBR support; query its capabilities and test the concrete build rather than assuming a generic fallback is visually correct.

The tag's Windows Direct3D workflow lanes are manually dispatched; alpha.1 has no automatic MinGW/Wine lane. See Tutorial 72 for the single- and multi-renderer modes, and verify PBR on the concrete renderer and driver you intend to ship.

Per-map UV channels and transforms

glTF lets every texture reference pick its own TEXCOORD set and apply an independent KHR_texture_transform. Alpha.1 carries the first two distinct authored sets into renderer-facing UV0/UV1, records a selector for each of the five core maps and both specular maps, and transports every map’s scale/rotation/translation independently.

A material requesting a third distinct authored set exceeds the two-channel vertex layouts. CNA falls that map back to packed channel 0 and adds a stable diagnostic to Model::getGltfImportReportEXTProperty(); both direct glTF and converter-generated .cnj models expose the report.

Where to go next

• Tutorial 115: CNAEXT — what the marker on these effects actually does.
• Tutorial 112: Skeletal Animation from glTF — driving SkinnedPbrEffect.
• Tutorial 37: Multiple Lights — the three-light convention in depth.
• Effects reference