62 lines
2.9 KiB
Markdown
62 lines
2.9 KiB
Markdown
Materials and Textures Overview (PBR)
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- PBR textures bound per material (set=1):
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- binding=0: GLTFMaterialData (UBO)
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- binding=1: `colorTex` (albedo/base color) — sRGB
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- binding=2: `metalRoughTex` (G=roughness, B=metallic) — UNORM
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- binding=3: `normalMap` (tangent-space normal, UNORM)
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- binding=4: `occlusionTex` (ambient occlusion, R channel) — UNORM
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- binding=5: `emissiveTex` (emissive RGB) — sRGB
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- G‑Buffer writes world‑space normals. Tangent‑space normal maps are decoded with TBN using a sign‑correct bitangent (B = sign * cross(N, T)).
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- Numeric fallbacks via `MaterialConstants` (CPU) / `GLTFMaterialData` (GPU):
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- `colorFactors` (RGBA). Defaults to 1 if zero.
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- `metal_rough_factors` (X=metallic, Y=roughness). Roughness is clamped to ≥ 0.04 in shaders.
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- `extra[0].x` = `normalScale` (scalar, default 1.0). Multiplies the XY of decoded normal.
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- `extra[0].y` = `aoStrength` (scalar, 0–1). Controls AO influence.
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- `extra[0].z` = `hasAO` (flag, 1 = use AO texture, 0 = skip).
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- `extra[1].rgb` = `emissiveFactor` (vec3). Multiplied with emissive texture.
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- `extra[2].x` = `alphaCutoff` (scalar). For MASK alpha mode.
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- Defaults when a texture is missing:
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- Albedo → checkerboard error texture
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- MR → white (no effect)
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- Normal → 1×1 flat normal (0.5, 0.5, 1.0)
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- Occlusion → 1×1 white (AO = 1.0, no occlusion)
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- Emissive → 1×1 black (no emission)
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Implications for primitive meshes
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- Primitives can use:
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- Albedo + MR + Normal textures, or
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- Numeric factors only, or
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- Any mix (missing textures fall back to defaults).
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Texture conventions
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- Albedo/base color: sRGB.
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- Metallic-Roughness: UNORM; channels: G=roughness, B=metallic.
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- Normal map: UNORM; expected +Y (green up). If your maps look inverted, flip the green channel offline.
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Notes on tangent space
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- Tangents are loaded from glTF when present (`TANGENT` attribute, vec4 where w is handedness).
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- If missing, the engine generates tangents:
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- Default: robust Gram–Schmidt with handedness.
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- Preferred: MikkTSpace (enabled by CMake option `ENABLE_MIKKTS=ON`).
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Notes on MikkTSpace
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- Recommended for parity with content tools. Enable at configure time: `-DENABLE_MIKKTS=ON`.
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- Falls back automatically to the internal generator if disabled or if MikkTS fails.
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Usage Examples
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- Adjust normal strength per material: set `material.constants.extra[0].x` (CPU) or `normalTexture.scale` in glTF.
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- Primitive with PBR textures:
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- Set `MeshMaterialDesc::Kind::Textured` and fill `albedoPath`, `metalRoughPath`, and `normalPath`.
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G-Buffer Outputs
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- The geometry pass (`gbuffer.frag`) writes 4 render targets:
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- `outPos` (location 0): World position (xyz) + valid flag (w=1).
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- `outNorm` (location 1): World normal (xyz) + roughness (w).
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- `outAlbedo` (location 2): Albedo (rgb) + metallic (a).
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- `outExtra` (location 3): AO (x) + emissive (yzw).
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- Deferred lighting reads these and computes:
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```glsl
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vec3 color = direct + indirect * ao + emissive;
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```
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