/** 
 * @file llvosurfacepatch.cpp
 * @brief Viewer-object derived "surface patch", which is a piece of terrain
 *
 * $LicenseInfo:firstyear=2001&license=viewerlgpl$
 * Second Life Viewer Source Code
 * Copyright (C) 2010, Linden Research, Inc.
 * 
 * This library is free software; you can redistribute it and/or
 * modify it under the terms of the GNU Lesser General Public
 * License as published by the Free Software Foundation;
 * version 2.1 of the License only.
 * 
 * This library is distributed in the hope that it will be useful,
 * but WITHOUT ANY WARRANTY; without even the implied warranty of
 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
 * Lesser General Public License for more details.
 * 
 * You should have received a copy of the GNU Lesser General Public
 * License along with this library; if not, write to the Free Software
 * Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA  02110-1301  USA
 * 
 * Linden Research, Inc., 945 Battery Street, San Francisco, CA  94111  USA
 * $/LicenseInfo$
 */

#include "llviewerprecompiledheaders.h"

#include "llvosurfacepatch.h"

#include "lldrawpoolterrain.h"

#include "lldrawable.h"
#include "llface.h"
#include "llprimitive.h"
#include "llsky.h"
#include "llsurfacepatch.h"
#include "llsurface.h"
#include "llviewerobjectlist.h"
#include "llviewerregion.h"
#include "llvlcomposition.h"
#include "llvovolume.h"
#include "pipeline.h"
#include "llspatialpartition.h"

F32 LLVOSurfacePatch::sLODFactor = 1.f;

//============================================================================

class LLVertexBufferTerrain : public LLVertexBuffer
{
public:
	LLVertexBufferTerrain() :
		LLVertexBuffer(MAP_VERTEX | MAP_NORMAL | MAP_TEXCOORD0 | MAP_TEXCOORD1 | MAP_COLOR, GL_DYNAMIC_DRAW)
	{
		//texture coordinates 2 and 3 exist, but use the same data as texture coordinate 1
	};

	// virtual
	void setupVertexBuffer(U32 data_mask)
	{	
		LLVertexBuffer::setupVertexBuffer(data_mask & ~(MAP_TEXCOORD2 | MAP_TEXCOORD3));
	}
};

//============================================================================

LLVOSurfacePatch::LLVOSurfacePatch(const LLUUID &id, const LLPCode pcode, LLViewerRegion *regionp)
	:	LLStaticViewerObject(id, pcode, regionp),
		mDirtiedPatch(FALSE),
		mPool(NULL),
		mBaseComp(0),
		mPatchp(NULL),
		mDirtyTexture(FALSE),
		mDirtyTerrain(FALSE),
		mLastNorthStride(0),
		mLastEastStride(0),
		mLastStride(0),
		mLastLength(0)
{
	// Terrain must draw during selection passes so it can block objects behind it.
	mbCanSelect = TRUE;
	setScale(LLVector3(16.f, 16.f, 16.f)); // Hack for setting scale for bounding boxes/visibility.
}


LLVOSurfacePatch::~LLVOSurfacePatch()
{
	mPatchp = NULL;
}


void LLVOSurfacePatch::markDead()
{
	if (mPatchp)
	{
		mPatchp->clearVObj();
		mPatchp = NULL;
	}
	LLViewerObject::markDead();
}


BOOL LLVOSurfacePatch::isActive() const
{
	return FALSE;
}


void LLVOSurfacePatch::setPixelAreaAndAngle(LLAgent &agent)
{
	mAppAngle = 50;
	mPixelArea = 500*500;
}


void LLVOSurfacePatch::updateTextures()
{
}


LLFacePool *LLVOSurfacePatch::getPool()
{
	mPool = (LLDrawPoolTerrain*) gPipeline.getPool(LLDrawPool::POOL_TERRAIN, mPatchp->getSurface()->getSTexture());

	return mPool;
}


LLDrawable *LLVOSurfacePatch::createDrawable(LLPipeline *pipeline)
{
	pipeline->allocDrawable(this);

	mDrawable->setRenderType(LLPipeline::RENDER_TYPE_TERRAIN);
	
	mBaseComp = llfloor(mPatchp->getMinComposition());
	S32 min_comp, max_comp, range;
	min_comp = llfloor(mPatchp->getMinComposition());
	max_comp = llceil(mPatchp->getMaxComposition());
	range = (max_comp - min_comp);
	range++;
	if (range > 3)
	{
		if ((mPatchp->getMinComposition() - min_comp) > (max_comp - mPatchp->getMaxComposition()))
		{
			// The top side runs over more
			mBaseComp++;
		}
		range = 3;
	}

	LLFacePool *poolp = getPool();

	mDrawable->addFace(poolp, NULL);

	return mDrawable;
}


void LLVOSurfacePatch::updateGL()
{
	if (mPatchp)
	{
		LL_PROFILE_ZONE_SCOPED
		mPatchp->updateGL();
	}
}

BOOL LLVOSurfacePatch::updateGeometry(LLDrawable *drawable)
{
    LL_PROFILE_ZONE_SCOPED;

	dirtySpatialGroup(TRUE);
	
	S32 min_comp, max_comp, range;
	min_comp = lltrunc(mPatchp->getMinComposition());
	max_comp = lltrunc(ceil(mPatchp->getMaxComposition()));
	range = (max_comp - min_comp);
	range++;
	S32 new_base_comp = lltrunc(mPatchp->getMinComposition());
	if (range > 3)
	{
		if ((mPatchp->getMinComposition() - min_comp) > (max_comp - mPatchp->getMaxComposition()))
		{
			// The top side runs over more
			new_base_comp++;
		}
		range = 3;
	}

	// Pick the two closest detail textures for this patch...
	// Then create the draw pool for it.
	// Actually, should get the average composition instead of the center.
	mBaseComp = new_base_comp;

	//////////////////////////
	//
	// Figure out the strides
	//
	//

	U32 patch_width, render_stride, north_stride, east_stride, length;
	render_stride = mPatchp->getRenderStride();
	patch_width = mPatchp->getSurface()->getGridsPerPatchEdge();

	length = patch_width / render_stride;

	if (mPatchp->getNeighborPatch(NORTH))
	{
		north_stride = mPatchp->getNeighborPatch(NORTH)->getRenderStride();
	}
	else
	{
		north_stride = render_stride;
	}

	if (mPatchp->getNeighborPatch(EAST))
	{
		east_stride = mPatchp->getNeighborPatch(EAST)->getRenderStride();
	}
	else
	{
		east_stride = render_stride;
	}

	mLastLength = length;
	mLastStride = render_stride;
	mLastNorthStride = north_stride;
	mLastEastStride = east_stride;

	return TRUE;
}

void LLVOSurfacePatch::updateFaceSize(S32 idx)
{
	if (idx != 0)
	{
		LL_WARNS() << "Terrain partition requested invalid face!!!" << LL_ENDL;
		return;
	}

	LLFace* facep = mDrawable->getFace(idx);
	if (facep)
	{
		S32 num_vertices = 0;
		S32 num_indices = 0;
	
		if (mLastStride)
		{
			getGeomSizesMain(mLastStride, num_vertices, num_indices);
			getGeomSizesNorth(mLastStride, mLastNorthStride, num_vertices, num_indices);
			getGeomSizesEast(mLastStride, mLastEastStride, num_vertices, num_indices);
		}

		facep->setSize(num_vertices, num_indices);	
	}
}

BOOL LLVOSurfacePatch::updateLOD()
{
	return TRUE;
}

void LLVOSurfacePatch::getGeometry(LLStrider<LLVector3> &verticesp,
								LLStrider<LLVector3> &normalsp,
								LLStrider<LLVector2> &texCoords0p,
								LLStrider<LLVector2> &texCoords1p,
								LLStrider<U16> &indicesp)
{
	LLFace* facep = mDrawable->getFace(0);
	if (facep)
	{
		U32 index_offset = facep->getGeomIndex();

		updateMainGeometry(facep, 
						verticesp,
						normalsp,
						texCoords0p,
						texCoords1p,
						indicesp,
						index_offset);
		updateNorthGeometry(facep, 
							verticesp,
							normalsp,
							texCoords0p,
							texCoords1p,
							indicesp,
							index_offset);
		updateEastGeometry(facep, 
							verticesp,
							normalsp,
							texCoords0p,
							texCoords1p,
							indicesp,
							index_offset);
	}
}

void LLVOSurfacePatch::updateMainGeometry(LLFace *facep,
										LLStrider<LLVector3> &verticesp,
										LLStrider<LLVector3> &normalsp,
										LLStrider<LLVector2> &texCoords0p,
										LLStrider<LLVector2> &texCoords1p,
										LLStrider<U16> &indicesp,
										U32 &index_offset)
{
	S32 i, j, x, y;

	U32 patch_size, render_stride;
	S32 num_vertices, num_indices;
	U32 index;

	llassert(mLastStride > 0);

	render_stride = mLastStride;
	patch_size = mPatchp->getSurface()->getGridsPerPatchEdge();
	S32 vert_size = patch_size / render_stride;

	///////////////////////////
	//
	// Render the main patch
	//
	//

	num_vertices = 0;
	num_indices = 0;
	// First, figure out how many vertices we need...
	getGeomSizesMain(render_stride, num_vertices, num_indices);

	if (num_vertices > 0)
	{
		facep->mCenterAgent = mPatchp->getPointAgent(8, 8);

		// Generate patch points first
		for (j = 0; j < vert_size; j++)
		{
			for (i = 0; i < vert_size; i++)
			{
				x = i * render_stride;
				y = j * render_stride;
				mPatchp->eval(x, y, render_stride, verticesp.get(), normalsp.get(), texCoords0p.get(), texCoords1p.get());
				verticesp++;
				normalsp++;
				texCoords0p++;
				texCoords1p++;
			}
		}

		for (j = 0; j < (vert_size - 1); j++)
		{
			if (j % 2)
			{
				for (i = (vert_size - 1); i > 0; i--)
				{
					index = (i - 1)+ j*vert_size;
					*(indicesp++) = index_offset + index;

					index = i + (j+1)*vert_size;
					*(indicesp++) = index_offset + index;

					index = (i - 1) + (j+1)*vert_size;
					*(indicesp++) = index_offset + index;

					index = (i - 1) + j*vert_size;
					*(indicesp++) = index_offset + index;

					index = i + j*vert_size;
					*(indicesp++) = index_offset + index;

					index = i + (j+1)*vert_size;
					*(indicesp++) = index_offset + index;
				}
			}
			else
			{
				for (i = 0; i < (vert_size - 1); i++)
				{
					index = i + j*vert_size;
					*(indicesp++) = index_offset + index;

					index = (i + 1) + (j+1)*vert_size;
					*(indicesp++) = index_offset + index;

					index = i + (j+1)*vert_size;
					*(indicesp++) = index_offset + index;

					index = i + j*vert_size;
					*(indicesp++) = index_offset + index;

					index = (i + 1) + j*vert_size;
					*(indicesp++) = index_offset + index;

					index = (i + 1) + (j + 1)*vert_size;
					*(indicesp++) = index_offset + index;
				}
			}
		}
	}
	index_offset += num_vertices;
}


void LLVOSurfacePatch::updateNorthGeometry(LLFace *facep,
										LLStrider<LLVector3> &verticesp,
										LLStrider<LLVector3> &normalsp,
										LLStrider<LLVector2> &texCoords0p,
										LLStrider<LLVector2> &texCoords1p,
										LLStrider<U16> &indicesp,
										U32 &index_offset)
{
	S32 i, x, y;

	S32 num_vertices;

	U32 render_stride = mLastStride;
	S32 patch_size = mPatchp->getSurface()->getGridsPerPatchEdge();
	S32 length = patch_size / render_stride;
	S32 half_length = length / 2;
	U32 north_stride = mLastNorthStride;
	
	///////////////////////////
	//
	// Render the north strip
	//
	//

	// Stride lengths are the same
	if (north_stride == render_stride)
	{
		num_vertices = 2 * length + 1;

		facep->mCenterAgent = (mPatchp->getPointAgent(8, 15) + mPatchp->getPointAgent(8, 16))*0.5f;

		// Main patch
		for (i = 0; i < length; i++)
		{
			x = i * render_stride;
			y = 16 - render_stride;

			mPatchp->eval(x, y, render_stride, verticesp.get(), normalsp.get(), texCoords0p.get(), texCoords1p.get());
			verticesp++;
			normalsp++;
			texCoords0p++;
			texCoords1p++;
		}

		// North patch
		for (i = 0; i <= length; i++)
		{
			x = i * render_stride;
			y = 16;
			mPatchp->eval(x, y, render_stride, verticesp.get(), normalsp.get(), texCoords0p.get(), texCoords1p.get());
			verticesp++;
			normalsp++;
			texCoords0p++;
			texCoords1p++;
		}


		for (i = 0; i < length; i++)
		{
			// Generate indices
			*(indicesp++) = index_offset + i;
			*(indicesp++) = index_offset + length + i + 1;
			*(indicesp++) = index_offset + length + i;

			if (i != length - 1)
			{
				*(indicesp++) = index_offset + i;
				*(indicesp++) = index_offset + i + 1;
				*(indicesp++) = index_offset + length + i + 1;
			}
		}
	}
	else if (north_stride > render_stride)
	{
		// North stride is longer (has less vertices)
		num_vertices = length + length/2 + 1;

		facep->mCenterAgent = (mPatchp->getPointAgent(7, 15) + mPatchp->getPointAgent(8, 16))*0.5f;

		// Iterate through this patch's points
		for (i = 0; i < length; i++)
		{
			x = i * render_stride;
			y = 16 - render_stride;

			mPatchp->eval(x, y, render_stride, verticesp.get(), normalsp.get(), texCoords0p.get(), texCoords1p.get());
			verticesp++;
			normalsp++;
			texCoords0p++;
			texCoords1p++;
		}

		// Iterate through the north patch's points
		for (i = 0; i <= length; i+=2)
		{
			x = i * render_stride;
			y = 16;

			mPatchp->eval(x, y, render_stride, verticesp.get(), normalsp.get(), texCoords0p.get(), texCoords1p.get());
			verticesp++;
			normalsp++;
			texCoords0p++;
			texCoords1p++;
		}


		for (i = 0; i < length; i++)
		{
			if (!(i % 2))
			{
				*(indicesp++) = index_offset + i;
				*(indicesp++) = index_offset + i + 1;
				*(indicesp++) = index_offset + length + (i/2);

				*(indicesp++) = index_offset + i + 1;
				*(indicesp++) = index_offset + length + (i/2) + 1;
				*(indicesp++) = index_offset + length + (i/2);
			}
			else if (i < (length - 1))
			{
				*(indicesp++) = index_offset + i;
				*(indicesp++) = index_offset + i + 1;
				*(indicesp++) = index_offset + length + (i/2) + 1;
			}
		}
	}
	else
	{
		// North stride is shorter (more vertices)
		length = patch_size / north_stride;
		half_length = length / 2;
		num_vertices = length + half_length + 1;

		facep->mCenterAgent = (mPatchp->getPointAgent(15, 7) + mPatchp->getPointAgent(16, 8))*0.5f;

		// Iterate through this patch's points
		for (i = 0; i < length; i+=2)
		{
			x = i * north_stride;
			y = 16 - render_stride;

			mPatchp->eval(x, y, render_stride, verticesp.get(), normalsp.get(), texCoords0p.get(), texCoords1p.get());
			verticesp++;
			normalsp++;
			texCoords0p++;
			texCoords1p++;
		}

		// Iterate through the north patch's points
		for (i = 0; i <= length; i++)
		{
			x = i * north_stride;
			y = 16;

			mPatchp->eval(x, y, render_stride, verticesp.get(), normalsp.get(), texCoords0p.get(), texCoords1p.get());
			verticesp++;
			normalsp++;
			texCoords0p++;
			texCoords1p++;
		}

		for (i = 0; i < length; i++)
		{
			if (!(i%2))
			{
				*(indicesp++) = index_offset + half_length + i;
				*(indicesp++) = index_offset + i/2;
				*(indicesp++) = index_offset + half_length + i + 1;
			}
			else if (i < (length - 2))
			{
				*(indicesp++) = index_offset + half_length + i;
				*(indicesp++) = index_offset + i/2;
				*(indicesp++) = index_offset + i/2 + 1;

				*(indicesp++) = index_offset + half_length + i;
				*(indicesp++) = index_offset + i/2 + 1;
				*(indicesp++) = index_offset + half_length + i + 1;
			}
			else
			{
				*(indicesp++) = index_offset + half_length + i;
				*(indicesp++) = index_offset + i/2;
				*(indicesp++) = index_offset + half_length + i + 1;
			}
		}
	}
	index_offset += num_vertices;
}

void LLVOSurfacePatch::updateEastGeometry(LLFace *facep,
										  LLStrider<LLVector3> &verticesp,
										  LLStrider<LLVector3> &normalsp,
										  LLStrider<LLVector2> &texCoords0p,
										  LLStrider<LLVector2> &texCoords1p,
										  LLStrider<U16> &indicesp,
										  U32 &index_offset)
{
	S32 i, x, y;

	S32 num_vertices;

	U32 render_stride = mLastStride;
	S32 patch_size = mPatchp->getSurface()->getGridsPerPatchEdge();
	S32 length = patch_size / render_stride;
	S32 half_length = length / 2;

	U32 east_stride = mLastEastStride;

	// Stride lengths are the same
	if (east_stride == render_stride)
	{
		num_vertices = 2 * length + 1;

		facep->mCenterAgent = (mPatchp->getPointAgent(8, 15) + mPatchp->getPointAgent(8, 16))*0.5f;

		// Main patch
		for (i = 0; i < length; i++)
		{
			x = 16 - render_stride;
			y = i * render_stride;

			mPatchp->eval(x, y, render_stride, verticesp.get(), normalsp.get(), texCoords0p.get(), texCoords1p.get());
			verticesp++;
			normalsp++;
			texCoords0p++;
			texCoords1p++;
		}

		// East patch
		for (i = 0; i <= length; i++)
		{
			x = 16;
			y = i * render_stride;
			mPatchp->eval(x, y, render_stride, verticesp.get(), normalsp.get(), texCoords0p.get(), texCoords1p.get());
			verticesp++;
			normalsp++;
			texCoords0p++;
			texCoords1p++;
		}


		for (i = 0; i < length; i++)
		{
			// Generate indices
			*(indicesp++) = index_offset + i;
			*(indicesp++) = index_offset + length + i;
			*(indicesp++) = index_offset + length + i + 1;

			if (i != length - 1)
			{
				*(indicesp++) = index_offset + i;
				*(indicesp++) = index_offset + length + i + 1;
				*(indicesp++) = index_offset + i + 1;
			}
		}
	}
	else if (east_stride > render_stride)
	{
		// East stride is longer (has less vertices)
		num_vertices = length + half_length + 1;

		facep->mCenterAgent = (mPatchp->getPointAgent(7, 15) + mPatchp->getPointAgent(8, 16))*0.5f;

		// Iterate through this patch's points
		for (i = 0; i < length; i++)
		{
			x = 16 - render_stride;
			y = i * render_stride;

			mPatchp->eval(x, y, render_stride, verticesp.get(), normalsp.get(), texCoords0p.get(), texCoords1p.get());
			verticesp++;
			normalsp++;
			texCoords0p++;
			texCoords1p++;
		}
		// Iterate through the east patch's points
		for (i = 0; i <= length; i+=2)
		{
			x = 16;
			y = i * render_stride;

			mPatchp->eval(x, y, render_stride, verticesp.get(), normalsp.get(), texCoords0p.get(), texCoords1p.get());
			verticesp++;
			normalsp++;
			texCoords0p++;
			texCoords1p++;
		}

		for (i = 0; i < length; i++)
		{
			if (!(i % 2))
			{
				*(indicesp++) = index_offset + i;
				*(indicesp++) = index_offset + length + (i/2);
				*(indicesp++) = index_offset + i + 1;

				*(indicesp++) = index_offset + i + 1;
				*(indicesp++) = index_offset + length + (i/2);
				*(indicesp++) = index_offset + length + (i/2) + 1;
			}
			else if (i < (length - 1))
			{
				*(indicesp++) = index_offset + i;
				*(indicesp++) = index_offset + length + (i/2) + 1;
				*(indicesp++) = index_offset + i + 1;
			}
		}
	}
	else
	{
		// East stride is shorter (more vertices)
		length = patch_size / east_stride;
		half_length = length / 2;
		num_vertices = length + length/2 + 1;

		facep->mCenterAgent = (mPatchp->getPointAgent(15, 7) + mPatchp->getPointAgent(16, 8))*0.5f;

		// Iterate through this patch's points
		for (i = 0; i < length; i+=2)
		{
			x = 16 - render_stride;
			y = i * east_stride;

			mPatchp->eval(x, y, render_stride, verticesp.get(), normalsp.get(), texCoords0p.get(), texCoords1p.get());
			verticesp++;
			normalsp++;
			texCoords0p++;
			texCoords1p++;
		}
		// Iterate through the east patch's points
		for (i = 0; i <= length; i++)
		{
			x = 16;
			y = i * east_stride;

			mPatchp->eval(x, y, render_stride, verticesp.get(), normalsp.get(), texCoords0p.get(), texCoords1p.get());
			verticesp++;
			normalsp++;
			texCoords0p++;
			texCoords1p++;
		}

		for (i = 0; i < length; i++)
		{
			if (!(i%2))
			{
				*(indicesp++) = index_offset + half_length + i;
				*(indicesp++) = index_offset + half_length + i + 1;
				*(indicesp++) = index_offset + i/2;
			}
			else if (i < (length - 2))
			{
				*(indicesp++) = index_offset + half_length + i;
				*(indicesp++) = index_offset + i/2 + 1;
				*(indicesp++) = index_offset + i/2;

				*(indicesp++) = index_offset + half_length + i;
				*(indicesp++) = index_offset + half_length + i + 1;
				*(indicesp++) = index_offset + i/2 + 1;
			}
			else
			{
				*(indicesp++) = index_offset + half_length + i;
				*(indicesp++) = index_offset + half_length + i + 1;
				*(indicesp++) = index_offset + i/2;
			}
		}
	}
	index_offset += num_vertices;
}

void LLVOSurfacePatch::setPatch(LLSurfacePatch *patchp)
{
	mPatchp = patchp;

	dirtyPatch();
};


void LLVOSurfacePatch::dirtyPatch()
{
	mDirtiedPatch = TRUE;
	dirtyGeom();
	mDirtyTerrain = TRUE;
	LLVector3 center = mPatchp->getCenterRegion();
	LLSurface *surfacep = mPatchp->getSurface();

	setPositionRegion(center);

	F32 scale_factor = surfacep->getGridsPerPatchEdge() * surfacep->getMetersPerGrid();
	setScale(LLVector3(scale_factor, scale_factor, mPatchp->getMaxZ() - mPatchp->getMinZ()));
}

void LLVOSurfacePatch::dirtyGeom()
{
	if (mDrawable)
	{
		gPipeline.markRebuild(mDrawable, LLDrawable::REBUILD_ALL, TRUE);
		LLFace* facep = mDrawable->getFace(0);
		if (facep)
		{
			facep->setVertexBuffer(NULL);
		}
		mDrawable->movePartition();
	}
}

void LLVOSurfacePatch::getGeomSizesMain(const S32 stride, S32 &num_vertices, S32 &num_indices)
{
	S32 patch_size = mPatchp->getSurface()->getGridsPerPatchEdge();

	// First, figure out how many vertices we need...
	S32 vert_size = patch_size / stride;
	if (vert_size >= 2)
	{
		num_vertices += vert_size * vert_size;
		num_indices += 6 * (vert_size - 1)*(vert_size - 1);
	}
}

void LLVOSurfacePatch::getGeomSizesNorth(const S32 stride, const S32 north_stride,
										 S32 &num_vertices, S32 &num_indices)
{
	S32 patch_size = mPatchp->getSurface()->getGridsPerPatchEdge();
	S32 length = patch_size / stride;
	// Stride lengths are the same
	if (north_stride == stride)
	{
		num_vertices += 2 * length + 1;
		num_indices += length * 6 - 3;
	}
	else if (north_stride > stride)
	{
		// North stride is longer (has less vertices)
		num_vertices += length + (length/2) + 1;
		num_indices += (length/2)*9 - 3;
	}
	else
	{
		// North stride is shorter (more vertices)
		length = patch_size / north_stride;
		num_vertices += length + (length/2) + 1;
		num_indices += 9*(length/2) - 3;
	}
}

void LLVOSurfacePatch::getGeomSizesEast(const S32 stride, const S32 east_stride,
										S32 &num_vertices, S32 &num_indices)
{
	S32 patch_size = mPatchp->getSurface()->getGridsPerPatchEdge();
	S32 length = patch_size / stride;
	// Stride lengths are the same
	if (east_stride == stride)
	{
		num_vertices += 2 * length + 1;
		num_indices += length * 6 - 3;
	}
	else if (east_stride > stride)
	{
		// East stride is longer (has less vertices)
		num_vertices += length + (length/2) + 1;
		num_indices += (length/2)*9 - 3;
	}
	else
	{
		// East stride is shorter (more vertices)
		length = patch_size / east_stride;
		num_vertices += length + (length/2) + 1;
		num_indices += 9*(length/2) - 3;
	}
}

BOOL LLVOSurfacePatch::lineSegmentIntersect(const LLVector4a& start, const LLVector4a& end, S32 face, BOOL pick_transparent, BOOL pick_rigged, S32 *face_hitp,
									  LLVector4a* intersection,LLVector2* tex_coord, LLVector4a* normal, LLVector4a* tangent)
	
{

	if (!lineSegmentBoundingBox(start, end))
	{
		return FALSE;
	}

	LLVector4a da;
	da.setSub(end, start);
	LLVector3 delta(da.getF32ptr());
		
	LLVector3 pdelta = delta;
	pdelta.mV[2] = 0;

	F32 plength = pdelta.length();
	
	F32 tdelta = 1.f/plength;

	LLVector3 v_start(start.getF32ptr());

	LLVector3 origin = v_start - mRegionp->getOriginAgent();

	if (mRegionp->getLandHeightRegion(origin) > origin.mV[2])
	{
		//origin is under ground, treat as no intersection
		return FALSE;
	}

	//step one meter at a time until intersection point found

	//VECTORIZE THIS
	const LLVector4a* exta = mDrawable->getSpatialExtents();

	LLVector3 ext[2];
	ext[0].set(exta[0].getF32ptr());
	ext[1].set(exta[1].getF32ptr());

	F32 rad = (delta*tdelta).magVecSquared();

	F32 t = 0.f;
	while ( t <= 1.f)
	{
		LLVector3 sample = origin + delta*t;
		
		if (AABBSphereIntersectR2(ext[0], ext[1], sample+mRegionp->getOriginAgent(), rad))
		{
			F32 height = mRegionp->getLandHeightRegion(sample);
			if (height > sample.mV[2])
			{ //ray went below ground, positive intersection
				//quick and dirty binary search to get impact point
				tdelta = -tdelta*0.5f;
				F32 err_dist = 0.001f;
				F32 dist = fabsf(sample.mV[2] - height);

				while (dist > err_dist && tdelta*tdelta > 0.0f)
				{
					t += tdelta;
					sample = origin+delta*t;
					height = mRegionp->getLandHeightRegion(sample);
					if ((tdelta < 0 && height < sample.mV[2]) ||
						(height > sample.mV[2] && tdelta > 0))
					{ //jumped over intersection point, go back
						tdelta = -tdelta;
					}
					tdelta *= 0.5f;
					dist = fabsf(sample.mV[2] - height);
				}

				if (intersection)
				{
					F32 height = mRegionp->getLandHeightRegion(sample);
					if (fabsf(sample.mV[2]-height) < delta.length()*tdelta)
					{
						sample.mV[2] = mRegionp->getLandHeightRegion(sample);
					}
					intersection->load3((sample + mRegionp->getOriginAgent()).mV);
				}

				if (normal)
				{
					normal->load3((mRegionp->getLand().resolveNormalGlobal(mRegionp->getPosGlobalFromRegion(sample))).mV);
				}

				return TRUE;
			}
		}

		t += tdelta;
		if (t > 1 && t < 1.f+tdelta*0.99f)
		{ //make sure end point is checked (saves vertical lines coming up negative)
			t = 1.f;
		}
	}


	return FALSE;
}

void LLVOSurfacePatch::updateSpatialExtents(LLVector4a& newMin, LLVector4a &newMax)
{
	LLVector3 posAgent = getPositionAgent();
	LLVector3 scale = getScale();
	//make z-axis scale at least 1 to avoid shadow artifacts on totally flat land
	scale.mV[VZ] = llmax(scale.mV[VZ], 1.f);
	newMin.load3( (posAgent-scale*0.5f).mV); // Changing to 2.f makes the culling a -little- better, but still wrong
	newMax.load3( (posAgent+scale*0.5f).mV);
	LLVector4a pos;
	pos.setAdd(newMin,newMax);
	pos.mul(0.5f);
	mDrawable->setPositionGroup(pos);
}

U32 LLVOSurfacePatch::getPartitionType() const
{ 
	return LLViewerRegion::PARTITION_TERRAIN; 
}

LLTerrainPartition::LLTerrainPartition(LLViewerRegion* regionp)
: LLSpatialPartition(LLDrawPoolTerrain::VERTEX_DATA_MASK, FALSE, GL_DYNAMIC_DRAW, regionp)
{
	mOcclusionEnabled = FALSE;
	mInfiniteFarClip = TRUE;
	mDrawableType = LLPipeline::RENDER_TYPE_TERRAIN;
	mPartitionType = LLViewerRegion::PARTITION_TERRAIN;
}

LLVertexBuffer* LLTerrainPartition::createVertexBuffer(U32 type_mask, U32 usage)
{
	return new LLVertexBufferTerrain();
}

void LLTerrainPartition::getGeometry(LLSpatialGroup* group)
{
    LL_PROFILE_ZONE_SCOPED;

	LLVertexBuffer* buffer = group->mVertexBuffer;

	//get vertex buffer striders
	LLStrider<LLVector3> vertices;
	LLStrider<LLVector3> normals;
	LLStrider<LLVector2> texcoords2;
	LLStrider<LLVector2> texcoords;
	LLStrider<U16> indices;

	llassert_always(buffer->getVertexStrider(vertices));
	llassert_always(buffer->getNormalStrider(normals));
	llassert_always(buffer->getTexCoord0Strider(texcoords));
	llassert_always(buffer->getTexCoord1Strider(texcoords2));
	llassert_always(buffer->getIndexStrider(indices));

	U32 indices_index = 0;
	U32 index_offset = 0;

	for (std::vector<LLFace*>::iterator i = mFaceList.begin(); i != mFaceList.end(); ++i)
	{
		LLFace* facep = *i;

		facep->setIndicesIndex(indices_index);
		facep->setGeomIndex(index_offset);
		facep->setVertexBuffer(buffer);

		LLVOSurfacePatch* patchp = (LLVOSurfacePatch*) facep->getViewerObject();
		patchp->getGeometry(vertices, normals, texcoords, texcoords2, indices);

		indices_index += facep->getIndicesCount();
		index_offset += facep->getGeomCount();
	}

	buffer->flush();
	mFaceList.clear();
}