acdream/src/AcDream.App/Rendering/Shaders/terrain_modern.vert

#version 460 core
#extension GL_ARB_bindless_texture : require

// Phase N.5b: terrain shader on the modern bindless dispatcher.
// Math identical to terrain.vert (Phase 3c per-cell mesh + Phase G AdjustPlanes
// lighting). The only structural change is the version + bindless extension
// — sampler access in the fragment stage is unchanged at the GLSL level.

layout(location = 0) in vec3  aPos;
layout(location = 1) in vec3  aNormal;
layout(location = 2) in uvec4 aPacked0;
layout(location = 3) in uvec4 aPacked1;
layout(location = 4) in uvec4 aPacked2;
layout(location = 5) in uvec4 aPacked3;

uniform mat4 uView;
uniform mat4 uProjection;

struct Light {
    vec4 posAndKind;
    vec4 dirAndRange;
    vec4 colorAndIntensity;
    vec4 coneAngleEtc;
};
layout(std140, binding = 1) uniform SceneLighting {
    Light uLights[8];
    vec4  uCellAmbient;
    vec4  uFogParams;
    vec4  uFogColor;
    vec4  uCameraAndTime;
};

// === Phase U.3: terrain screen-space clip gate (OutsideView region) ===========
// Terrain is a single global region (the OutsideView), so it needs one set of
// clip planes, not a per-instance slot table like the mesh shader. A std140 UBO
// at binding=2 carries it. The UBO binding namespace is distinct from the SSBO
// binding namespace, so this does NOT collide with the mesh shader's SSBO
// binding=2 — and within THIS shader binding=1 (SceneLighting) is the only other
// UBO, leaving binding=2 free. uTerrainClipCount == 0 (the U.3 default) ungates
// terrain entirely (the second loop sets all 8 distances to +1.0). Uploaded by
// ClipFrame.UploadShared each frame; TerrainModernRenderer binds it before draw.
layout(std140, binding = 2) uniform TerrainClip {
    int  uTerrainClipCount;
    vec4 uTerrainClipPlanes[8];
};

// Core profile: redeclare gl_PerVertex so writing gl_ClipDistance[] is legal.
// Sized 8 to match GL_MAX_CLIP_DISTANCES >= 8. Host enables GL_CLIP_DISTANCE0..7
// once at startup; unused planes are set to +1.0 below so they pass everything.
out gl_PerVertex {
    vec4  gl_Position;
    float gl_ClipDistance[8];
};

out vec2  vBaseUV;
out vec3  vWorldNormal;
out vec3  vWorldPos;
out vec3  vLightingRGB;
out vec4  vOverlay0;
out vec4  vOverlay1;
out vec4  vOverlay2;
out vec4  vRoad0;
out vec4  vRoad1;
flat out float vBaseTexIdx;

// Retail's N·L floor from FUN_00532440 lines 2119/2138/2157/2176 at
// chunk_00530000.c (AdjustPlanes). The decompile reads:
//   if (fVar3 < DAT_00796344) fVar3 = DAT_00796344;
// applied to the clamped Lambert result BEFORE it's multiplied into
// dirColor. DAT_00796344's exact literal isn't pinned by the decompile
// but every other "floor" use in retail clamps negatives to zero (the
// physically-correct Lambert half-space). Our previous 0.08 was a
// defensive guess from early acdream days that made back-lit terrain
// visibly brighter than retail (user-observed 2026-04-24 "acdream
// warmer / less blue than retail"). Reverting to 0.0 matches retail
// per the decompile and lets ambient fill in the back side.
// Cross-ref: docs/research/2026-04-24-lambert-brightness-split.md.
const float MIN_FACTOR = 0.0;

vec4 unpackOverlayLayer(uint texIdxU, uint alphaIdxU, uint rotIdx, vec2 baseUV) {
    float texIdx   = float(texIdxU);
    float alphaIdx = float(alphaIdxU);
    if (texIdx   >= 254.0) texIdx   = -1.0;
    if (alphaIdx >= 254.0) alphaIdx = -1.0;

    vec2 rotatedUV = baseUV;
    if      (rotIdx == 1u) rotatedUV = vec2(1.0 - baseUV.y,       baseUV.x);
    else if (rotIdx == 2u) rotatedUV = vec2(1.0 - baseUV.x, 1.0 - baseUV.y);
    else if (rotIdx == 3u) rotatedUV = vec2(      baseUV.y, 1.0 - baseUV.x);

    return vec4(rotatedUV.x, rotatedUV.y, texIdx, alphaIdx);
}

void main() {
    // Unpack rotation fields from aPacked3. Bit layout (data3):
    //   .x  (byte 0): bits 0-1 rotBase (unused), 2-3 rotOvl0, 4-5 rotOvl1, 6-7 rotOvl2
    //   .y  (byte 1): bits 0-1 rotRd0 (= data3 bit 8-9),
    //                 bits 2-3 rotRd1 (= data3 bit 10-11),
    //                 bit  4   splitDir (= data3 bit 12)
    uint rotOvl0 = (aPacked3.x >> 2u) & 3u;
    uint rotOvl1 = (aPacked3.x >> 4u) & 3u;
    uint rotOvl2 = (aPacked3.x >> 6u) & 3u;
    uint rotRd0  =  aPacked3.y        & 3u;
    uint rotRd1  = (aPacked3.y >> 2u) & 3u;
    uint splitDir= (aPacked3.y >> 4u) & 1u;

    // Derive which of the 4 cell corners this vertex represents from
    // gl_VertexID % 6. The CPU-side LandblockMesh emits vertices in a
    // specific order for each split direction; the tables below must stay
    // in lockstep with LandblockMesh.Build's SWtoNE/SEtoNW branches.
    // 2026-04-21 fix: geometry re-derived to match ACE's ConstructPolygons
    // convention. SWtoNE (cut BL→TR, y=x diagonal) now maps to the {BL,BR,TR}
    // + {BL,TR,TL} triangle pair; SEtoNW (cut BR→TL, x+y=1 diagonal) maps to
    // {BL,BR,TL} + {BR,TR,TL}.
    int vIdx = gl_VertexID % 6;
    int corner = 0;
    if (splitDir == 0u) {
        // SWtoNE order: BL, BR, TR, BL, TR, TL  → corners 0, 1, 2, 0, 2, 3
        if      (vIdx == 0) corner = 0;
        else if (vIdx == 1) corner = 1;
        else if (vIdx == 2) corner = 2;
        else if (vIdx == 3) corner = 0;
        else if (vIdx == 4) corner = 2;
        else                corner = 3;
    } else {
        // SEtoNW order: BL, BR, TL, BR, TR, TL  → corners 0, 1, 3, 1, 2, 3
        if      (vIdx == 0) corner = 0;
        else if (vIdx == 1) corner = 1;
        else if (vIdx == 2) corner = 3;
        else if (vIdx == 3) corner = 1;
        else if (vIdx == 4) corner = 2;
        else                corner = 3;
    }

    vec2 baseUV;
    if      (corner == 0) baseUV = vec2(0.0, 1.0);
    else if (corner == 1) baseUV = vec2(1.0, 1.0);
    else if (corner == 2) baseUV = vec2(1.0, 0.0);
    else                  baseUV = vec2(0.0, 0.0);

    vBaseUV = baseUV;
    vWorldPos = aPos;
    vWorldNormal = normalize(aNormal);

    // Retail AdjustPlanes bake (terrain.vert:124-134 — identical math).
    vec3 sunDir = uLights[0].dirAndRange.xyz;
    vec3 sunCol = uLights[0].colorAndIntensity.xyz * uLights[0].colorAndIntensity.w;
    float L = max(dot(vWorldNormal, -sunDir), MIN_FACTOR);
    vLightingRGB = sunCol * L + uCellAmbient.xyz;

    float baseTex = float(aPacked0.x);
    if (baseTex >= 254.0) baseTex = -1.0;
    vBaseTexIdx = baseTex;

    vOverlay0 = unpackOverlayLayer(aPacked0.z, aPacked0.w, rotOvl0, baseUV);
    vOverlay1 = unpackOverlayLayer(aPacked1.x, aPacked1.y, rotOvl1, baseUV);
    vOverlay2 = unpackOverlayLayer(aPacked1.z, aPacked1.w, rotOvl2, baseUV);
    vRoad0    = unpackOverlayLayer(aPacked2.x, aPacked2.y, rotRd0,  baseUV);
    vRoad1    = unpackOverlayLayer(aPacked2.z, aPacked2.w, rotRd1,  baseUV);

    // Retail zFightTerrainAdjust (acclient_2013_pseudo_c.txt:1120769 = 0.00999999978,
    // applied per terrain vertex inside ACRender::landPolysDraw at line 702254,
    // address 006b6402). Render terrain 1 cm below its physical Z so coplanar
    // building floors win the depth test. Physics path is unaffected — it reads
    // the un-nudged heightmap via TerrainSurface.SampleZ.
    // Closes issue #100; supersedes the hiddenTerrainCells cell-collapse hack.
    vec3 terrainPos = vec3(aPos.xy, aPos.z - 0.01);
    gl_Position = uProjection * uView * vec4(terrainPos, 1.0);

    // Phase U.3: terrain clip gate against the single OutsideView region. With
    // uTerrainClipCount == 0 (U.3 default) the first loop is skipped and the
    // second sets all 8 distances to +1.0 ⇒ no clipping ⇒ identical terrain.
    for (int i = 0; i < uTerrainClipCount; ++i)
        gl_ClipDistance[i] = dot(uTerrainClipPlanes[i], gl_Position);
    for (int i = uTerrainClipCount; i < 8; ++i)
        gl_ClipDistance[i] = 1.0;
}