#Bugfix(terrain): stop black terrain cells on maps with more than 32 terrain textures.

The per-material splat bake gave every terrain material its own weight channel across the whole map, and the
terrain pixel shader reads at most 32 (8 weight textures x 4 channels, with every ps_3_0 sampler already in use).
Materials past the 32nd got no channel, their cells summed zero weight and drew pure black. USA mission 1 uses 37.
Slot selection was also keyed on a texture's position in the map's list rather than on the materials in use.

Weight channels are now reused per draw tile:
- The bake scans every 32-cell draw-tile window plus a 4-cell apron, records which materials meet, and colours
  that conflict graph: materials that ever share a window never share a channel. USA mission 1: 37 materials
  in 13 channels.
- Each cell stores the materials within the apron. Each draw tile ORs its cells and uploads its own
  channel-to-material region table and enable mask before drawing; the result is cached until the draw window
  slides or the map rebakes.
- On additive atlas-page passes, a tile with nothing on that page is skipped.
- The bake serial the tile cache keys on is global, so a new map allocated at the old map's address cannot
  reuse its tables.
- The pixel shader is unchanged; its material loop now runs only over the channels in use.

Added a [TERRAIN] readout (materials, channels, dropped cells, pages, most materials per tile), off by default,
and extends the bake log. Design, limits and the constants the apron is tied to
the dedicated terrain splat map doc file, Appendix E.

Author: )2onin 4 ever!!

Core/GameEngineDevice/Include/W3DDevice/GameClient/WorldHeightMap.h

@@ -379,6 +379,22 @@ class WorldHeightMap : public RefCountClass,
 		return (activeIdx >= 0 && activeIdx < m_numActiveMaterials)
 			? m_activeMaterialIndices[activeIdx] : -1;
 	}
+	// Ronin @diagnostic 14/09/2026 DX9: §19e.3. For the [TERRAIN] readout.
+	Int  getSplatWeightableClasses() const { return m_splatWeightableClasses; }
+	Int  getSplatDroppedCells() const      { return m_splatDroppedCells; }
+	Int  getSplatMaxPerTile() const        { return m_splatMaxPerTile; }
+	Int  getSplatChannelsNeeded() const    { return m_splatChannelsNeeded; }
+	// Ronin @bugfix 14/09/2026 DX9: §19e.3. Channel reuse — materials within the bake apron of a DRAW-LOCAL cell (same coordinates as
+	// getTerrainTexturePageForCell), as compact bits; OR these over a draw tile and hand the result to buildSplatRegionTable.
+	UnsignedInt64 getSplatCellMaskForCell(Int xIndex, Int yIndex) const {
+		const Int x = xIndex + m_drawOriginX;
+		const Int y = yIndex + m_drawOriginY;
+		return (x >= 0 && y >= 0 && x < m_width && y < m_height && (Int)m_splatCellMask.size() == m_width * m_height)
+			? m_splatCellMask[y * m_width + x] : 0;
+	}
+	Int  getSplatBakeSerial() const { return m_splatBakeSerial; }
+	Int  buildSplatRegionTable(UnsignedInt64 presentMask, Int terrainPage,
+		float* outRegionA, float* outRegionB, float* outSlotEnableMask) const;
 
 	// @feature Ronin 29/04/2026 Splat S20-A2d2: public read-only accessors for the
 	// weight-atlas pages allocated by ensurePerMaterialWeightAtlasTextures().
@@ -396,6 +412,18 @@ class WorldHeightMap : public RefCountClass,
 	// Bake state. Cleared by freeMapResources(); allocated by buildPerMaterialWeightTextures().
 	Int            m_numActiveMaterials = 0;
 	Int            m_activeMaterialIndices[SPLAT_MAX_ACTIVE_MATERIALS] = {};
+	// Ronin @diagnostic 14/09/2026 DX9: §19e.3. Bake readout: classes the bake can weight, cells left with no channel.
+	Int            m_splatWeightableClasses = 0;
+	Int            m_splatDroppedCells = 0;
+	Int            m_splatMaxPerTile = 0;
+	Int            m_splatChannelsNeeded = 0;
+	// Ronin @bugfix 14/09/2026 DX9: §19e.3. Channel reuse: compact material -> class and -> weight channel, per-cell material masks.
+	Int            m_splatNumCompact = 0;
+	Int            m_splatCompactClass[64] = {};
+	Int            m_splatCompactChannel[64] = {};
+	std::vector<UnsignedInt64> m_splatCellMask;
+	Int            m_splatBakeSerial = 0;
+
 	UnsignedByte* m_perMaterialWeightBytes = nullptr;   // [activeIdx][texelY*pitch + texelX], one byte per texel
 	Int            m_perMaterialWeightWidth = 0;
 	Int            m_perMaterialWeightHeight = 0;

Core/GameEngineDevice/Source/W3DDevice/GameClient/HeightMap.cpp

@@ -3015,51 +3015,50 @@ void HeightMapRenderObjClass::renderPrimaryBlendControlPass()
 
 	Bool drewAnyContribution = FALSE;
 
+	// Ronin @bugfix 14/09/2026 DX9: §19e.3. CHANNEL REUSE — per draw tile, the materials around its cells. Cached until the draw
+	// window slides or the bake reruns; same draw-local cell mapping as the paged-terrain cache above.
+	static std::vector<UnsignedInt64> s_tileMaterialMask;
+	static const WorldHeightMap* s_tileMaskMap = nullptr;
+	static Int s_tileMaskKey[6] = { -1, -1, -1, -1, -1, -1 };
+	{
+		const Int keyNow[6] = { m_originX, m_originY, m_map->getDrawOrgX(), m_map->getDrawOrgY(),
+								m_map->getSplatBakeSerial(), m_numVBTilesX * 4096 + m_numVBTilesY };
+		Bool stale = (s_tileMaskMap != m_map) || ((Int)s_tileMaterialMask.size() != m_numVBTilesX * m_numVBTilesY);
+		for (Int k = 0; k < 6; ++k) {
+			if (keyNow[k] != s_tileMaskKey[k]) stale = TRUE;
+		}
+		if (stale) {
+			s_tileMaskMap = m_map;
+			for (Int k = 0; k < 6; ++k) s_tileMaskKey[k] = keyNow[k];
+			s_tileMaterialMask.assign(m_numVBTilesX * m_numVBTilesY, 0);
+			for (Int tj = 0; tj < m_numVBTilesY; ++tj) {
+				for (Int ti = 0; ti < m_numVBTilesX; ++ti) {
+					Int ccX = VERTEX_BUFFER_TILE_LENGTH, ccY = VERTEX_BUFFER_TILE_LENGTH;
+					if (ti == m_numVBTilesX - 1 && m_numBlockColumnsInLastVB > 0) ccX = m_numBlockColumnsInLastVB;
+					if (tj == m_numVBTilesY - 1 && m_numBlockRowsInLastVB > 0) ccY = m_numBlockRowsInLastVB;
+					UnsignedInt64 mask = 0;
+					for (Int ly = 0; ly < ccY; ++ly) {
+						const Int mY = getYWithOrigin(tj * VERTEX_BUFFER_TILE_LENGTH + ly);
+						for (Int lx = 0; lx < ccX; ++lx)
+							mask |= m_map->getSplatCellMaskForCell(getXWithOrigin(ti * VERTEX_BUFFER_TILE_LENGTH + lx), mY);
+					}
+					s_tileMaterialMask[tj * m_numVBTilesX + ti] = mask;
+				}
+			}
+		}
+	}
+	const Int pmNumSlots = m_map->getActiveMaterialCount();	// weight channels in use; the shader loops this many slots
+
 	for (Int terrainPage = 0; terrainPage < terrainPageCount; ++terrainPage) {
 		TextureClass* pTerrainAtlas =
 			useMultiPageAccumulation ? m_map->getTerrainTexture(terrainPage) : m_stageZeroTexture;
 		if (pTerrainAtlas == nullptr) {
 			continue;
 		}
-
-		float pmRegionA[WorldHeightMap::SPLAT_MAX_ACTIVE_MATERIALS * 4];
-		float pmRegionB[WorldHeightMap::SPLAT_MAX_ACTIVE_MATERIALS * 4];
-		float pmSlotEnableMask[WorldHeightMap::SPLAT_MAX_ACTIVE_MATERIALS];
-
-		Int pmNumSlots = 0;
-		if (useMultiPageAccumulation) {
-			pmNumSlots = m_map->getSplatAtlasRegionsForActiveSetPage(
-				terrainPage, pmRegionA, pmRegionB, pmSlotEnableMask);
-		}
-		else {
-			pmNumSlots = m_map->getSplatAtlasRegionsForActiveSet(pmRegionA, pmRegionB);
-			for (Int s = 0; s < WorldHeightMap::SPLAT_MAX_ACTIVE_MATERIALS; ++s) {
-				pmSlotEnableMask[s] = (s < pmNumSlots) ? 1.0f : 0.0f;
-			}
-		}
-
-		// @debug Ronin 03/05/2026 Splat S20: viz modes need to see ALL active slots so
-		// the heatmap / wSum reflects the full material set, not just one page's subset.
-		if (forceSinglePassForViz) {
-			for (Int s = 0; s < WorldHeightMap::SPLAT_MAX_ACTIVE_MATERIALS; ++s) {
-				pmSlotEnableMask[s] = (s < pmNumSlots) ? 1.0f : 0.0f;
-			}
-		}
-
 		if (pmNumSlots <= 0) {
 			continue;
 		}
 
-		Int pageEnabledSlots = 0;
-		for (Int s = 0; s < pmNumSlots; ++s) {
-			if (pmSlotEnableMask[s] > 0.5f) {
-				++pageEnabledSlots;
-			}
-		}
-		if (pageEnabledSlots <= 0) {
-			continue;
-		}
-
 		const float pmActiveCount[4] = { (float)pmNumSlots, 0.0f, 0.0f, 0.0f };
 
 		W3DShaderManager::setTexture(0, pTerrainAtlas);
@@ -3074,16 +3073,8 @@ void HeightMapRenderObjClass::renderPrimaryBlendControlPass()
 			IDirect3DDevice9* pPmDev = DX8Wrapper::_Get_D3D_Device8();
 			if (pPmDev) {
 				pPmDev->SetPixelShaderConstantF(0, pmControlParams, 1);
-				pPmDev->SetPixelShaderConstantF(1, pmRegionA, WorldHeightMap::SPLAT_MAX_ACTIVE_MATERIALS);
-				pPmDev->SetPixelShaderConstantF(
-					1 + WorldHeightMap::SPLAT_MAX_ACTIVE_MATERIALS,
-					pmRegionB,
-					WorldHeightMap::SPLAT_MAX_ACTIVE_MATERIALS);
+				// Ronin @bugfix 14/09/2026 DX9: §19e.3. c1..c64 and c68..c75 go up per draw tile (channel reuse), not per pass.
 				pPmDev->SetPixelShaderConstantF(65, pmActiveCount, 1);
-				pPmDev->SetPixelShaderConstantF(
-					68,
-					pmSlotEnableMask,
-					WorldHeightMap::SPLAT_MAX_ACTIVE_MATERIALS / 4);
 
 				{
 					// @bugfix Ronin 11/05/2026 Splat S20 / Normal-map N3: explicit sampler
@@ -3285,11 +3276,36 @@ void HeightMapRenderObjClass::renderPrimaryBlendControlPass()
 				}
 			}
 
+			// Ronin @bugfix 14/09/2026 DX9: §19e.3. Each tile uploads its OWN channel table. After the first accumulated draw, a tile
+			// with no material on this page adds nothing and is skipped.
+			const Bool passIsAdditive = useMultiPageAccumulation && drewAnyContribution;
+			IDirect3DDevice9* pTileDev = DX8Wrapper::_Get_D3D_Device8();
 			for (Int pmJ = 0; pmJ < m_numVBTilesY; ++pmJ) {
 				for (Int pmI = 0; pmI < m_numVBTilesX; ++pmI) {
 					// Ronin @perf 30/08/2026 DX9: §29i.3. Depth pass only — FALSE in every other pass.
 					if (shadowDepthSkipTile(pmI, pmJ, m_numVBTilesX))
 						continue;
+
+					float pmRegionA[WorldHeightMap::SPLAT_MAX_ACTIVE_MATERIALS * 4];
+					float pmRegionB[WorldHeightMap::SPLAT_MAX_ACTIVE_MATERIALS * 4];
+					float pmSlotEnableMask[WorldHeightMap::SPLAT_MAX_ACTIVE_MATERIALS];
+					const Int tileEnabled = m_map->buildSplatRegionTable(
+						s_tileMaterialMask[pmJ * m_numVBTilesX + pmI],
+						useMultiPageAccumulation ? terrainPage : -1,
+						pmRegionA, pmRegionB, pmSlotEnableMask);
+					if (tileEnabled <= 0 && passIsAdditive)
+						continue;
+					if (forceSinglePassForViz) {
+						for (Int s = 0; s < WorldHeightMap::SPLAT_MAX_ACTIVE_MATERIALS; ++s)
+							pmSlotEnableMask[s] = (s < pmNumSlots) ? 1.0f : 0.0f;
+					}
+					if (pTileDev) {
+						pTileDev->SetPixelShaderConstantF(1, pmRegionA, WorldHeightMap::SPLAT_MAX_ACTIVE_MATERIALS);
+						pTileDev->SetPixelShaderConstantF(1 + WorldHeightMap::SPLAT_MAX_ACTIVE_MATERIALS, pmRegionB,
+							WorldHeightMap::SPLAT_MAX_ACTIVE_MATERIALS);
+						pTileDev->SetPixelShaderConstantF(68, pmSlotEnableMask, WorldHeightMap::SPLAT_MAX_ACTIVE_MATERIALS / 4);
+					}
+
 					DX8Wrapper::Set_Vertex_Buffer(getVertexBufferTile(pmI, pmJ));
 					if (Is_Hidden() == 0) {
 						DX8Wrapper::Draw_Triangles(0, HEIGHTMAP_POLYGON_NUM, 0, HEIGHTMAP_VERTEX_NUM);