bvle-voxels/shaders/voxelTopingPS.hlsl

// BVLE Voxels - Toping Pixel Shader (Phase 4.2)
// Simplified version of voxelPS: triplanar texture sampling + basic lighting.
// No height-based blending (topings are small decorative meshes).

#include "voxelCommon.hlsli"

Texture2DArray<float4> materialTextures : register(t1);
SamplerState texSampler : register(s0);

struct PSInput {
    float4 position : SV_POSITION;
    float3 worldPos : WORLDPOS;
    float3 normal   : NORMAL;
    nointerpolation uint materialID : MATERIALID;
};

struct PSOutput {
    float4 color  : SV_TARGET0;
    float4 normal : SV_TARGET1;
};

[RootSignature(VOXEL_ROOTSIG)]
PSOutput main(PSInput input) {
    PSOutput output;
    float3 N = normalize(input.normal);
    float tiling = textureTiling;

    // Material texture index (materialID 1-5 → array layer 0-4)
    uint texIdx = clamp(input.materialID - 1u, 0u, 4u);

    // Triplanar sampling (same as voxel PS)
    float3 blend = abs(N);
    blend = blend / (blend.x + blend.y + blend.z + 0.001);

    float4 xSample = materialTextures.Sample(texSampler, float3(input.worldPos.yz * tiling, (float)texIdx));
    float4 ySample = materialTextures.Sample(texSampler, float3(input.worldPos.xz * tiling, (float)texIdx));
    float4 zSample = materialTextures.Sample(texSampler, float3(input.worldPos.xy * tiling, (float)texIdx));

    float3 texColor = (xSample.rgb * blend.x + ySample.rgb * blend.y + zSample.rgb * blend.z);

    float3 L = normalize(-sunDirection.xyz);
    float rawNdotL = dot(N, L);

    // ── Material-dependent lighting ─────────────────────────────
    // Stone (materialID=3): standard diffuse like voxel faces
    // Vegetation (grass etc.): stylized wrap lighting + translucency
    //   inspired by Airborn Trees (simonschreibt.de/gat/airborn-trees/)

    float3 lit;
    if (input.materialID == 3u) {
        // Stone: classic Lambert + cool ambient (matches voxel PS)
        float NdotL = max(rawNdotL, 0.0);
        float3 ambient = float3(0.15, 0.18, 0.25);
        lit = texColor * (sunColor.rgb * NdotL + ambient);
    } else {
        // ── Vegetation: soft wrap lighting ──────────────────────
        // Half-Lambert: wraps light around the surface, no hard terminator
        float halfLambert = rawNdotL * 0.5 + 0.5;
        float wrap = halfLambert * halfLambert; // squared for falloff shape

        // Diffuse floor: even fully back-facing blades get some sun contribution
        // Simulates light scattering through dense grass (cheap GI approximation)
        wrap = max(wrap, 0.35);

        // Translucency: thin blades let light through from behind
        // Stronger effect to reduce contrast when orbiting around grass
        float3 V = normalize(cameraPosition.xyz - input.worldPos);
        float backLight = saturate(dot(V, L));
        float transAmount = (1.0 - saturate(rawNdotL)) * 0.6;
        float translucency = backLight * transAmount;

        // Higher ambient for vegetation: grass blades bounce light between each other
        // (simplified inter-reflection / GI), brighter than stone ambient
        float3 ambient = float3(0.30, 0.33, 0.35);

        // Wrap + translucency for soft, low-contrast vegetation shading
        float3 diffuse = sunColor.rgb * (wrap * 0.88 + translucency * 0.55);
        lit = texColor * (diffuse + ambient);
    }

    output.color = float4(lit, 1.0);
    output.normal = float4(N, 0.0);
    return output;
}