PatchRData.cpp

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/* Copyright (C) 2013 Wildfire Games.
 * This file is part of 0 A.D.
 *
 * 0 A.D. is free software: you can redistribute it and/or modify
 * it under the terms of the GNU General Public License as published by
 * the Free Software Foundation, either version 2 of the License, or
 * (at your option) any later version.
 *
 * 0 A.D. 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 General Public License for more details.
 *
 * You should have received a copy of the GNU General Public License
 * along with 0 A.D.  If not, see <http://www.gnu.org/licenses/>.
 */

#include "precompiled.h"

#include <set>
#include <algorithm>
#include <numeric>

#include "graphics/GameView.h"
#include "graphics/LightEnv.h"
#include "graphics/LOSTexture.h"
#include "graphics/Patch.h"
#include "graphics/ShaderManager.h"
#include "graphics/Terrain.h"
#include "graphics/TextRenderer.h"
#include "lib/alignment.h"
#include "lib/allocators/arena.h"
#include "maths/MathUtil.h"
#include "ps/CLogger.h"
#include "ps/Game.h"
#include "ps/Profile.h"
#include "ps/Pyrogenesis.h"
#include "ps/World.h"
#include "ps/GameSetup/Config.h"
#include "renderer/AlphaMapCalculator.h"
#include "renderer/PatchRData.h"
#include "renderer/TerrainRenderer.h"
#include "renderer/Renderer.h"
#include "renderer/WaterManager.h"
#include "simulation2/Simulation2.h"
#include "simulation2/components/ICmpWaterManager.h"

const ssize_t BlendOffsets[9][2] = {
    {  0, -1 },
    { -1, -1 },
    { -1,  0 },
    { -1,  1 },
    {  0,  1 },
    {  1,  1 },
    {  1,  0 },
    {  1, -1 },
    {  0,  0 }
};

///////////////////////////////////////////////////////////////////
// CPatchRData constructor
CPatchRData::CPatchRData(CPatch* patch, CSimulation2* simulation) :
    m_Patch(patch), m_VBSides(0),
    m_VBBase(0), m_VBBaseIndices(0),
    m_VBBlends(0), m_VBBlendIndices(0),
    m_VBWater(0), m_VBWaterIndices(0),
    m_Simulation(simulation)
{
    ENSURE(patch);
    Build();
}

///////////////////////////////////////////////////////////////////
// CPatchRData destructor
CPatchRData::~CPatchRData()
{
    // release vertex buffer chunks
    if (m_VBSides) g_VBMan.Release(m_VBSides);
    if (m_VBBase) g_VBMan.Release(m_VBBase);
    if (m_VBBaseIndices) g_VBMan.Release(m_VBBaseIndices);
    if (m_VBBlends) g_VBMan.Release(m_VBBlends);
    if (m_VBBlendIndices) g_VBMan.Release(m_VBBlendIndices);
    if (m_VBWater) g_VBMan.Release(m_VBWater);
    if (m_VBWaterIndices) g_VBMan.Release(m_VBWaterIndices);
}

/**
 * Represents a blend for a single tile, texture and shape.
 */
struct STileBlend
{
    CTerrainTextureEntry* m_Texture;
    int m_Priority;
    u16 m_TileMask; // bit n set if this blend contains neighbour tile BlendOffsets[n]

    struct DecreasingPriority
    {
        bool operator()(const STileBlend& a, const STileBlend& b) const
        {
            if (a.m_Priority > b.m_Priority)
                return true;
            if (a.m_Priority < b.m_Priority)
                return false;
            if (a.m_Texture && b.m_Texture)
                return a.m_Texture->GetTag() > b.m_Texture->GetTag();
            return false;
        }
    };

    struct CurrentTile
    {
        bool operator()(const STileBlend& a) const
        {
            return (a.m_TileMask & (1 << 8)) != 0;
        }
    };
};

/**
 * Represents the ordered collection of blends drawn on a particular tile.
 */
struct STileBlendStack
{
    u8 i, j;
    std::vector<STileBlend> blends; // back of vector is lowest-priority texture
};

/**
 * Represents a batched collection of blends using the same texture.
 */
struct SBlendLayer
{
    struct Tile
    {
        u8 i, j;
        u8 shape;
    };

    CTerrainTextureEntry* m_Texture;
    std::vector<Tile> m_Tiles;
};

void CPatchRData::BuildBlends()
{
    PROFILE3("build blends");

    m_BlendSplats.clear();

    std::vector<SBlendVertex> blendVertices;
    std::vector<u16> blendIndices;

    CTerrain* terrain = m_Patch->m_Parent;

    std::vector<STileBlendStack> blendStacks;
    blendStacks.reserve(PATCH_SIZE*PATCH_SIZE);

    // For each tile in patch ..
    for (ssize_t j = 0; j < PATCH_SIZE; ++j)
    {
        for (ssize_t i = 0; i < PATCH_SIZE; ++i)
        {
            ssize_t gx = m_Patch->m_X * PATCH_SIZE + i;
            ssize_t gz = m_Patch->m_Z * PATCH_SIZE + j;

            std::vector<STileBlend> blends;
            blends.reserve(9);

            // Compute a blend for every tile in the 3x3 square around this tile
            for (size_t n = 0; n < 9; ++n)
            {
                ssize_t ox = gx + BlendOffsets[n][1];
                ssize_t oz = gz + BlendOffsets[n][0];

                CMiniPatch* nmp = terrain->GetTile(ox, oz);
                if (!nmp)
                    continue;

                STileBlend blend;
                blend.m_Texture = nmp->GetTextureEntry();
                blend.m_Priority = nmp->GetPriority();
                blend.m_TileMask = 1 << n;
                blends.push_back(blend);
            }

            // Sort the blends, highest priority first
            std::sort(blends.begin(), blends.end(), STileBlend::DecreasingPriority());

            STileBlendStack blendStack;
            blendStack.i = i;
            blendStack.j = j;

            // Put the blends into the tile's stack, merging any adjacent blends with the same texture
            for (size_t k = 0; k < blends.size(); ++k)
            {
                if (!blendStack.blends.empty() && blendStack.blends.back().m_Texture == blends[k].m_Texture)
                    blendStack.blends.back().m_TileMask |= blends[k].m_TileMask;
                else
                    blendStack.blends.push_back(blends[k]);
            }

            // Remove blends that are after (i.e. lower priority than) the current tile
            // (including the current tile), since we don't want to render them on top of
            // the tile's base texture
            blendStack.blends.erase(
                std::find_if(blendStack.blends.begin(), blendStack.blends.end(), STileBlend::CurrentTile()),
                blendStack.blends.end());

            blendStacks.push_back(blendStack);
        }
    }

    // Given the blend stack per tile, we want to batch together as many blends as possible.
    // Group them into a series of layers (each of which has a single texture):
    // (This is effectively a topological sort / linearisation of the partial order induced
    // by the per-tile stacks, preferring to make tiles with equal textures adjacent.)

    std::vector<SBlendLayer> blendLayers;

    while (true)
    {
        if (!blendLayers.empty())
        {
            // Try to grab as many tiles as possible that match our current layer,
            // from off the blend stacks of all the tiles

            CTerrainTextureEntry* tex = blendLayers.back().m_Texture;

            for (size_t k = 0; k < blendStacks.size(); ++k)
            {
                if (!blendStacks[k].blends.empty() && blendStacks[k].blends.back().m_Texture == tex)
                {
                    SBlendLayer::Tile t = { blendStacks[k].i, blendStacks[k].j, (u8)blendStacks[k].blends.back().m_TileMask };
                    blendLayers.back().m_Tiles.push_back(t);
                    blendStacks[k].blends.pop_back();
                }
                // (We've already merged adjacent entries of the same texture in each stack,
                // so we don't need to bother looping to check the next entry in this stack again)
            }
        }

        // We've grabbed as many tiles as possible; now we need to start a new layer.
        // The new layer's texture could come from the back of any non-empty stack;
        // choose the longest stack as a heuristic to reduce the number of layers
        CTerrainTextureEntry* bestTex = NULL;
        size_t bestStackSize = 0;

        for (size_t k = 0; k < blendStacks.size(); ++k)
        {
            if (blendStacks[k].blends.size() > bestStackSize)
            {
                bestStackSize = blendStacks[k].blends.size();
                bestTex = blendStacks[k].blends.back().m_Texture;
            }
        }

        // If all our stacks were empty, we're done
        if (bestStackSize == 0)
            break;

        // Otherwise add the new layer, then loop back and start filling it in

        SBlendLayer layer;
        layer.m_Texture = bestTex;
        blendLayers.push_back(layer);
    }

    // Now build outgoing splats
    m_BlendSplats.resize(blendLayers.size());

    for (size_t k = 0; k < blendLayers.size(); ++k)
    {
        SSplat& splat = m_BlendSplats[k];
        splat.m_IndexStart = blendIndices.size();
        splat.m_Texture = blendLayers[k].m_Texture;

        for (size_t t = 0; t < blendLayers[k].m_Tiles.size(); ++t)
        {
            SBlendLayer::Tile& tile = blendLayers[k].m_Tiles[t];
            AddBlend(blendVertices, blendIndices, tile.i, tile.j, tile.shape, splat.m_Texture);
        }

        splat.m_IndexCount = blendIndices.size() - splat.m_IndexStart;
    }

    // Release existing vertex buffer chunks
    if (m_VBBlends)
    {
        g_VBMan.Release(m_VBBlends);
        m_VBBlends = 0;
    }

    if (m_VBBlendIndices)
    {
        g_VBMan.Release(m_VBBlendIndices);
        m_VBBlendIndices = 0;
    }

    if (blendVertices.size())
    {
        // Construct vertex buffer

        m_VBBlends = g_VBMan.Allocate(sizeof(SBlendVertex), blendVertices.size(), GL_STATIC_DRAW, GL_ARRAY_BUFFER);
        m_VBBlends->m_Owner->UpdateChunkVertices(m_VBBlends, &blendVertices[0]);

        // Update the indices to include the base offset of the vertex data
        for (size_t k = 0; k < blendIndices.size(); ++k)
            blendIndices[k] += m_VBBlends->m_Index;

        m_VBBlendIndices = g_VBMan.Allocate(sizeof(u16), blendIndices.size(), GL_STATIC_DRAW, GL_ELEMENT_ARRAY_BUFFER);
        m_VBBlendIndices->m_Owner->UpdateChunkVertices(m_VBBlendIndices, &blendIndices[0]);
    }
}

void CPatchRData::AddBlend(std::vector<SBlendVertex>& blendVertices, std::vector<u16>& blendIndices, 
               u16 i, u16 j, u8 shape, CTerrainTextureEntry* texture)
{
    CTerrain* terrain = m_Patch->m_Parent;

    ssize_t gx = m_Patch->m_X * PATCH_SIZE + i;
    ssize_t gz = m_Patch->m_Z * PATCH_SIZE + j;

    // uses the current neighbour texture
    BlendShape8 shape8;
    for (size_t m = 0; m < 8; ++m)
        shape8[m] = (shape & (1 << m)) ? 0 : 1;

    // calculate the required alphamap and the required rotation of the alphamap from blendshape
    unsigned int alphamapflags;
    int alphamap = CAlphaMapCalculator::Calculate(shape8, alphamapflags);

    // now actually render the blend tile (if we need one)
    if (alphamap == -1)
        return;
    
    float u0 = texture->m_TerrainAlpha->second.m_AlphaMapCoords[alphamap].u0;
    float u1 = texture->m_TerrainAlpha->second.m_AlphaMapCoords[alphamap].u1;
    float v0 = texture->m_TerrainAlpha->second.m_AlphaMapCoords[alphamap].v0;
    float v1 = texture->m_TerrainAlpha->second.m_AlphaMapCoords[alphamap].v1;

    if (alphamapflags & BLENDMAP_FLIPU)
        std::swap(u0, u1);

    if (alphamapflags & BLENDMAP_FLIPV)
        std::swap(v0, v1);

    int base = 0;
    if (alphamapflags & BLENDMAP_ROTATE90)
        base = 1;
    else if (alphamapflags & BLENDMAP_ROTATE180)
        base = 2;
    else if (alphamapflags & BLENDMAP_ROTATE270)
        base = 3;

    SBlendVertex vtx[4];
    vtx[(base + 0) % 4].m_AlphaUVs[0] = u0;
    vtx[(base + 0) % 4].m_AlphaUVs[1] = v0;
    vtx[(base + 1) % 4].m_AlphaUVs[0] = u1;
    vtx[(base + 1) % 4].m_AlphaUVs[1] = v0;
    vtx[(base + 2) % 4].m_AlphaUVs[0] = u1;
    vtx[(base + 2) % 4].m_AlphaUVs[1] = v1;
    vtx[(base + 3) % 4].m_AlphaUVs[0] = u0;
    vtx[(base + 3) % 4].m_AlphaUVs[1] = v1;

    SBlendVertex dst;

    const CLightEnv& lightEnv = g_Renderer.GetLightEnv();
    CVector3D normal;

    bool cpuLighting = (g_Renderer.GetRenderPath() == CRenderer::RP_FIXED);

    size_t index = blendVertices.size();

    terrain->CalcPosition(gx, gz, dst.m_Position);
    terrain->CalcNormal(gx, gz, normal);
    dst.m_Normal = normal;
    dst.m_DiffuseColor = cpuLighting ? lightEnv.EvaluateTerrainDiffuseScaled(normal) : lightEnv.EvaluateTerrainDiffuseFactor(normal);
    dst.m_AlphaUVs[0] = vtx[0].m_AlphaUVs[0];
    dst.m_AlphaUVs[1] = vtx[0].m_AlphaUVs[1];
    blendVertices.push_back(dst);

    terrain->CalcPosition(gx + 1, gz, dst.m_Position);
    terrain->CalcNormal(gx + 1, gz, normal);
    dst.m_Normal = normal;
    dst.m_DiffuseColor = cpuLighting ? lightEnv.EvaluateTerrainDiffuseScaled(normal) : lightEnv.EvaluateTerrainDiffuseFactor(normal);
    dst.m_AlphaUVs[0] = vtx[1].m_AlphaUVs[0];
    dst.m_AlphaUVs[1] = vtx[1].m_AlphaUVs[1];
    blendVertices.push_back(dst);

    terrain->CalcPosition(gx + 1, gz + 1, dst.m_Position);
    terrain->CalcNormal(gx + 1, gz + 1, normal);
    dst.m_Normal = normal;
    dst.m_DiffuseColor = cpuLighting ? lightEnv.EvaluateTerrainDiffuseScaled(normal) : lightEnv.EvaluateTerrainDiffuseFactor(normal);
    dst.m_AlphaUVs[0] = vtx[2].m_AlphaUVs[0];
    dst.m_AlphaUVs[1] = vtx[2].m_AlphaUVs[1];
    blendVertices.push_back(dst);

    terrain->CalcPosition(gx, gz + 1, dst.m_Position);
    terrain->CalcNormal(gx, gz + 1, normal);
    dst.m_Normal = normal;
    dst.m_DiffuseColor = cpuLighting ? lightEnv.EvaluateTerrainDiffuseScaled(normal) : lightEnv.EvaluateTerrainDiffuseFactor(normal);
    dst.m_AlphaUVs[0] = vtx[3].m_AlphaUVs[0];
    dst.m_AlphaUVs[1] = vtx[3].m_AlphaUVs[1];
    blendVertices.push_back(dst);

    bool dir = terrain->GetTriangulationDir(gx, gz);
    if (dir)
    {
        blendIndices.push_back(index+0);
        blendIndices.push_back(index+1);
        blendIndices.push_back(index+3);

        blendIndices.push_back(index+1);
        blendIndices.push_back(index+2);
        blendIndices.push_back(index+3);
    }
    else
    {
        blendIndices.push_back(index+0);
        blendIndices.push_back(index+1);
        blendIndices.push_back(index+2);

        blendIndices.push_back(index+2);
        blendIndices.push_back(index+3);
        blendIndices.push_back(index+0);
    }
}

void CPatchRData::BuildIndices()
{
    PROFILE3("build indices");

    CTerrain* terrain = m_Patch->m_Parent;

    ssize_t px = m_Patch->m_X * PATCH_SIZE;
    ssize_t pz = m_Patch->m_Z * PATCH_SIZE;

    // must have allocated some vertices before trying to build corresponding indices
    ENSURE(m_VBBase);

    // number of vertices in each direction in each patch
    ssize_t vsize=PATCH_SIZE+1;

    std::vector<unsigned short> indices;
    indices.reserve(PATCH_SIZE * PATCH_SIZE * 4);

    // release existing splats
    m_Splats.clear();

    // build grid of textures on this patch
    std::vector<CTerrainTextureEntry*> textures;
    CTerrainTextureEntry* texgrid[PATCH_SIZE][PATCH_SIZE];
    for (ssize_t j=0;j<PATCH_SIZE;j++) {
        for (ssize_t i=0;i<PATCH_SIZE;i++) {
            CTerrainTextureEntry* tex=m_Patch->m_MiniPatches[j][i].GetTextureEntry();
            texgrid[j][i]=tex;
            if (std::find(textures.begin(),textures.end(),tex)==textures.end()) {
                textures.push_back(tex);
            }
        }
    }

    // now build base splats from interior textures
    m_Splats.resize(textures.size());
    // build indices for base splats
    size_t base=m_VBBase->m_Index;
    ENSURE(base + vsize*vsize < 65536); // mustn't overflow u16 indexes
    for (size_t i=0;i<m_Splats.size();i++) {
        CTerrainTextureEntry* tex=textures[i];

        SSplat& splat=m_Splats[i];
        splat.m_Texture=tex;
        splat.m_IndexStart=indices.size();

        for (ssize_t j = 0; j < PATCH_SIZE; j++)
        {
            for (ssize_t i = 0; i < PATCH_SIZE; i++)
            {
                if (texgrid[j][i] == tex)
                {
                    bool dir = terrain->GetTriangulationDir(px+i, pz+j);
                    if (dir)
                    {
                        indices.push_back(u16(((j+0)*vsize+(i+0))+base));
                        indices.push_back(u16(((j+0)*vsize+(i+1))+base));
                        indices.push_back(u16(((j+1)*vsize+(i+0))+base));

                        indices.push_back(u16(((j+0)*vsize+(i+1))+base));
                        indices.push_back(u16(((j+1)*vsize+(i+1))+base));
                        indices.push_back(u16(((j+1)*vsize+(i+0))+base));
                    }
                    else
                    {
                        indices.push_back(u16(((j+0)*vsize+(i+0))+base));
                        indices.push_back(u16(((j+0)*vsize+(i+1))+base));
                        indices.push_back(u16(((j+1)*vsize+(i+1))+base));

                        indices.push_back(u16(((j+1)*vsize+(i+1))+base));
                        indices.push_back(u16(((j+1)*vsize+(i+0))+base));
                        indices.push_back(u16(((j+0)*vsize+(i+0))+base));
                    }
                }
            }
        }
        splat.m_IndexCount=indices.size()-splat.m_IndexStart;
    }

    // Release existing vertex buffer chunk
    if (m_VBBaseIndices)
    {
        g_VBMan.Release(m_VBBaseIndices);
        m_VBBaseIndices = 0;
    }

    ENSURE(indices.size());

    // Construct vertex buffer
    m_VBBaseIndices = g_VBMan.Allocate(sizeof(u16), indices.size(), GL_STATIC_DRAW, GL_ELEMENT_ARRAY_BUFFER);
    m_VBBaseIndices->m_Owner->UpdateChunkVertices(m_VBBaseIndices, &indices[0]);
}


void CPatchRData::BuildVertices()
{
    PROFILE3("build vertices");

    // create both vertices and lighting colors

    // number of vertices in each direction in each patch
    ssize_t vsize=PATCH_SIZE+1;

    std::vector<SBaseVertex> vertices;
    vertices.resize(vsize*vsize);

    // get index of this patch
    ssize_t px=m_Patch->m_X;
    ssize_t pz=m_Patch->m_Z;

    CTerrain* terrain=m_Patch->m_Parent;
    const CLightEnv& lightEnv = g_Renderer.GetLightEnv();

    bool cpuLighting = (g_Renderer.GetRenderPath() == CRenderer::RP_FIXED);

    // build vertices
    for (ssize_t j=0;j<vsize;j++) {
        for (ssize_t i=0;i<vsize;i++) {
            ssize_t ix=px*PATCH_SIZE+i;
            ssize_t iz=pz*PATCH_SIZE+j;
            ssize_t v=(j*vsize)+i;

            // calculate vertex data
            terrain->CalcPosition(ix,iz,vertices[v].m_Position);

            // Calculate diffuse lighting for this vertex
            // Ambient is added by the lighting pass (since ambient is the same
            // for all vertices, it need not be stored in the vertex structure)
            CVector3D normal;
            terrain->CalcNormal(ix,iz,normal);
            
            vertices[v].m_Normal = normal;

            vertices[v].m_DiffuseColor = cpuLighting ? lightEnv.EvaluateTerrainDiffuseScaled(normal) : lightEnv.EvaluateTerrainDiffuseFactor(normal);
        }
    }

    // upload to vertex buffer
    if (!m_VBBase)
        m_VBBase = g_VBMan.Allocate(sizeof(SBaseVertex), vsize * vsize, GL_STATIC_DRAW, GL_ARRAY_BUFFER);

    m_VBBase->m_Owner->UpdateChunkVertices(m_VBBase, &vertices[0]);
}

void CPatchRData::BuildSide(std::vector<SSideVertex>& vertices, CPatchSideFlags side)
{
    ssize_t vsize = PATCH_SIZE + 1;
    CTerrain* terrain = m_Patch->m_Parent;
    CmpPtr<ICmpWaterManager> cmpWaterManager(*m_Simulation, SYSTEM_ENTITY);

    for (ssize_t k = 0; k < vsize; k++)
    {
        ssize_t gx = m_Patch->m_X * PATCH_SIZE;
        ssize_t gz = m_Patch->m_Z * PATCH_SIZE;
        switch (side)
        {
        case CPATCH_SIDE_NEGX: gz += k; break;
        case CPATCH_SIDE_POSX: gx += PATCH_SIZE; gz += PATCH_SIZE-k; break;
        case CPATCH_SIDE_NEGZ: gx += PATCH_SIZE-k; break;
        case CPATCH_SIDE_POSZ: gz += PATCH_SIZE; gx += k; break;
        }

        CVector3D pos;
        terrain->CalcPosition(gx, gz, pos);

        // Clamp the height to the water level
        float waterHeight = 0.f;
        if (cmpWaterManager)
            waterHeight = cmpWaterManager->GetExactWaterLevel(pos.X, pos.Z);
        pos.Y = std::max(pos.Y, waterHeight);

        SSideVertex v0, v1;
        v0.m_Position = pos;
        v1.m_Position = pos;
        v1.m_Position.Y = 0;

        // If this is the start of this tristrip, but we've already got a partial
        // tristrip, add a couple of degenerate triangles to join the strips properly
        if (k == 0 && !vertices.empty())
        {
            vertices.push_back(vertices.back());
            vertices.push_back(v1);
        }

        // Now add the new triangles
        vertices.push_back(v1);
        vertices.push_back(v0);
    }
}

void CPatchRData::BuildSides()
{
    PROFILE3("build sides");

    std::vector<SSideVertex> sideVertices;

    int sideFlags = m_Patch->GetSideFlags();

    // If no sides are enabled, we don't need to do anything
    if (!sideFlags)
        return;

    // For each side, generate a tristrip by adding a vertex at ground/water
    // level and a vertex underneath at height 0.

    if (sideFlags & CPATCH_SIDE_NEGX)
        BuildSide(sideVertices, CPATCH_SIDE_NEGX);

    if (sideFlags & CPATCH_SIDE_POSX)
        BuildSide(sideVertices, CPATCH_SIDE_POSX);

    if (sideFlags & CPATCH_SIDE_NEGZ)
        BuildSide(sideVertices, CPATCH_SIDE_NEGZ);

    if (sideFlags & CPATCH_SIDE_POSZ)
        BuildSide(sideVertices, CPATCH_SIDE_POSZ);

    if (sideVertices.empty())
        return;

    if (!m_VBSides)
        m_VBSides = g_VBMan.Allocate(sizeof(SSideVertex), sideVertices.size(), GL_STATIC_DRAW, GL_ARRAY_BUFFER);
    m_VBSides->m_Owner->UpdateChunkVertices(m_VBSides, &sideVertices[0]);
}

void CPatchRData::Build()
{
    BuildVertices();
    BuildSides();
    BuildIndices();
    BuildBlends();
    BuildWater();
}

void CPatchRData::Update(CSimulation2* simulation)
{
    m_Simulation = simulation;
    if (m_UpdateFlags!=0) {
        // TODO,RC 11/04/04 - need to only rebuild necessary bits of renderdata rather
        // than everything; it's complicated slightly because the blends are dependent
        // on both vertex and index data
        BuildVertices();
        BuildSides();
        BuildIndices();
        BuildBlends();
        BuildWater();

        m_UpdateFlags=0;
    }
}

// Types used for glMultiDrawElements batching:

// To minimise the cost of memory allocations, everything used for computing
// batches uses a arena allocator. (All allocations are short-lived so we can
// just throw away the whole arena at the end of each frame.)

// std::map types with appropriate arena allocators and default comparison operator
#define POOLED_BATCH_MAP(Key, Value) \
    std::map<Key, Value, std::less<Key>, ProxyAllocator<std::pair<Key const, Value>, Allocators::DynamicArena > >

// Equivalent to "m[k]", when it returns a arena-allocated std::map (since we can't
// use the default constructor in that case)
template<typename M>
typename M::mapped_type& PooledMapGet(M& m, const typename M::key_type& k, Allocators::DynamicArena& arena)
{
    return m.insert(std::make_pair(k,
        typename M::mapped_type(typename M::mapped_type::key_compare(), typename M::mapped_type::allocator_type(arena))
    )).first->second;
}

// Equivalent to "m[k]", when it returns a std::pair of arena-allocated std::vectors
template<typename M>
typename M::mapped_type& PooledPairGet(M& m, const typename M::key_type& k, Allocators::DynamicArena& arena)
{
    return m.insert(std::make_pair(k, std::make_pair(
            typename M::mapped_type::first_type(typename M::mapped_type::first_type::allocator_type(arena)),
            typename M::mapped_type::second_type(typename M::mapped_type::second_type::allocator_type(arena))
    ))).first->second;
}

// Each multidraw batch has a list of index counts, and a list of pointers-to-first-indexes
typedef std::pair<std::vector<GLint, ProxyAllocator<GLint, Allocators::DynamicArena > >, std::vector<void*, ProxyAllocator<void*, Allocators::DynamicArena > > > BatchElements;

// Group batches by index buffer
typedef POOLED_BATCH_MAP(CVertexBuffer*, BatchElements) IndexBufferBatches;

// Group batches by vertex buffer
typedef POOLED_BATCH_MAP(CVertexBuffer*, IndexBufferBatches) VertexBufferBatches;

// Group batches by texture
typedef POOLED_BATCH_MAP(CTerrainTextureEntry*, VertexBufferBatches) TextureBatches;

void CPatchRData::RenderBases(const std::vector<CPatchRData*>& patches, const CShaderDefines& context, 
                  ShadowMap* shadow, bool isDummyShader, const CShaderProgramPtr& dummy)
{
    Allocators::DynamicArena arena(1 * MiB);

    TextureBatches batches (TextureBatches::key_compare(), (TextureBatches::allocator_type(arena)));

    PROFILE_START("compute batches");

    // Collect all the patches' base splats into their appropriate batches
    for (size_t i = 0; i < patches.size(); ++i)
    {
        CPatchRData* patch = patches[i];
        for (size_t j = 0; j < patch->m_Splats.size(); ++j)
        {
            SSplat& splat = patch->m_Splats[j];

            BatchElements& batch = PooledPairGet(
                PooledMapGet(
                    PooledMapGet(batches, splat.m_Texture, arena),
                    patch->m_VBBase->m_Owner, arena
                ),
                patch->m_VBBaseIndices->m_Owner, arena
            );

            batch.first.push_back(splat.m_IndexCount);

            u8* indexBase = patch->m_VBBaseIndices->m_Owner->GetBindAddress();
            batch.second.push_back(indexBase + sizeof(u16)*(patch->m_VBBaseIndices->m_Index + splat.m_IndexStart));
        }
    }

    PROFILE_END("compute batches");

    // Render each batch
    for (TextureBatches::iterator itt = batches.begin(); itt != batches.end(); ++itt)
    {
        int numPasses = 1;
        
        CShaderTechniquePtr techBase;
        
        if (!isDummyShader)
        {
            if (itt->first->GetMaterial().GetShaderEffect().length() == 0)
            {
                LOGERROR(L"Terrain renderer failed to load shader effect.\n");
                continue;
            }
                        
            techBase = g_Renderer.GetShaderManager().LoadEffect(itt->first->GetMaterial().GetShaderEffect(),
                        context, itt->first->GetMaterial().GetShaderDefines(0));
            
            numPasses = techBase->GetNumPasses();
        }
        
        for (int pass = 0; pass < numPasses; ++pass)
        {
            if (!isDummyShader)
            {
                techBase->BeginPass(pass);
                TerrainRenderer::PrepareShader(techBase->GetShader(), shadow);
            }
            
            const CShaderProgramPtr& shader = isDummyShader ? dummy : techBase->GetShader(pass);
            
            if (itt->first->GetMaterial().GetSamplers().size() != 0)
            {
                const CMaterial::SamplersVector& samplers = itt->first->GetMaterial().GetSamplers();
                size_t samplersNum = samplers.size();
                
                for (size_t s = 0; s < samplersNum; ++s)
                {
                    const CMaterial::TextureSampler& samp = samplers[s];
                    shader->BindTexture(samp.Name, samp.Sampler);
                }
                
                itt->first->GetMaterial().GetStaticUniforms().BindUniforms(shader);

#if !CONFIG2_GLES
                if (isDummyShader)
                {
                    glMatrixMode(GL_TEXTURE);
                    glLoadMatrixf(itt->first->GetTextureMatrix());
                    glMatrixMode(GL_MODELVIEW);
                }
                else
#endif
                {
                    float c = itt->first->GetTextureMatrix()[0];
                    float ms = itt->first->GetTextureMatrix()[8];
                    shader->Uniform(str_textureTransform, c, ms, -ms, 0.f);
                }
            }
            else
            {
                shader->BindTexture(str_baseTex, g_Renderer.GetTextureManager().GetErrorTexture());
            }

            for (VertexBufferBatches::iterator itv = itt->second.begin(); itv != itt->second.end(); ++itv)
            {
                GLsizei stride = sizeof(SBaseVertex);
                SBaseVertex *base = (SBaseVertex *)itv->first->Bind();
                shader->VertexPointer(3, GL_FLOAT, stride, &base->m_Position[0]);
                shader->ColorPointer(4, GL_UNSIGNED_BYTE, stride, &base->m_DiffuseColor);
                shader->NormalPointer(GL_FLOAT, stride, &base->m_Normal[0]);
                shader->TexCoordPointer(GL_TEXTURE0, 3, GL_FLOAT, stride, &base->m_Position[0]);

                shader->AssertPointersBound();

                for (IndexBufferBatches::iterator it = itv->second.begin(); it != itv->second.end(); ++it)
                {
                    it->first->Bind();

                    BatchElements& batch = it->second;

                    if (!g_Renderer.m_SkipSubmit)
                    {
                        // Don't use glMultiDrawElements here since it doesn't have a significant
                        // performance impact and it suffers from various driver bugs (e.g. it breaks
                        // in Mesa 7.10 swrast with index VBOs)
                        for (size_t i = 0; i < batch.first.size(); ++i)
                            glDrawElements(GL_TRIANGLES, batch.first[i], GL_UNSIGNED_SHORT, batch.second[i]);
                    }

                    g_Renderer.m_Stats.m_DrawCalls++;
                    g_Renderer.m_Stats.m_TerrainTris += std::accumulate(batch.first.begin(), batch.first.end(), 0) / 3;
                }
            }
            
            if (!isDummyShader)
                techBase->EndPass();
        }
    }

#if !CONFIG2_GLES
    if (isDummyShader)
    {
        glMatrixMode(GL_TEXTURE);
        glLoadIdentity();
        glMatrixMode(GL_MODELVIEW);
    }
#endif

    CVertexBuffer::Unbind();
}

/**
 * Helper structure for RenderBlends.
 */
struct SBlendBatch
{
    SBlendBatch(Allocators::DynamicArena& arena) :
        m_Batches(VertexBufferBatches::key_compare(), VertexBufferBatches::allocator_type(arena))
    {
    }

    CTerrainTextureEntry* m_Texture;
    VertexBufferBatches m_Batches;
};

/**
 * Helper structure for RenderBlends.
 */
struct SBlendStackItem
{
    SBlendStackItem(CVertexBuffer::VBChunk* v, CVertexBuffer::VBChunk* i,
            const std::vector<CPatchRData::SSplat>& s, Allocators::DynamicArena& arena) :
        vertices(v), indices(i), splats(s.begin(), s.end(), SplatStack::allocator_type(arena))
    {
    }

    typedef std::vector<CPatchRData::SSplat, ProxyAllocator<CPatchRData::SSplat, Allocators::DynamicArena > > SplatStack;
    CVertexBuffer::VBChunk* vertices;
    CVertexBuffer::VBChunk* indices;
    SplatStack splats;
};

void CPatchRData::RenderBlends(const std::vector<CPatchRData*>& patches, const CShaderDefines& context, 
                  ShadowMap* shadow, bool isDummyShader, const CShaderProgramPtr& dummy)
{
    Allocators::DynamicArena arena(1 * MiB);

    typedef std::vector<SBlendBatch, ProxyAllocator<SBlendBatch, Allocators::DynamicArena > > BatchesStack;
    BatchesStack batches((BatchesStack::allocator_type(arena)));
    
    CShaderDefines contextBlend = context;
    contextBlend.Add(str_BLEND, str_1);

    PROFILE_START("compute batches");

    // Reserve an arbitrary size that's probably big enough in most cases,
    // to avoid heavy reallocations
    batches.reserve(256);

    typedef std::vector<SBlendStackItem, ProxyAllocator<SBlendStackItem, Allocators::DynamicArena > > BlendStacks;
    BlendStacks blendStacks((BlendStacks::allocator_type(arena)));
    blendStacks.reserve(patches.size());

    // Extract all the blend splats from each patch
    for (size_t i = 0; i < patches.size(); ++i)
    {
        CPatchRData* patch = patches[i];
        if (!patch->m_BlendSplats.empty())
        {

            blendStacks.push_back(SBlendStackItem(patch->m_VBBlends, patch->m_VBBlendIndices, patch->m_BlendSplats, arena));
            // Reverse the splats so the first to be rendered is at the back of the list
            std::reverse(blendStacks.back().splats.begin(), blendStacks.back().splats.end());
        }
    }

    // Rearrange the collection of splats to be grouped by texture, preserving
    // order of splats within each patch:
    // (This is exactly the same algorithm used in CPatchRData::BuildBlends,
    // but applied to patch-sized splats rather than to tile-sized splats;
    // see that function for comments on the algorithm.)
    while (true)
    {
        if (!batches.empty())
        {
            CTerrainTextureEntry* tex = batches.back().m_Texture;

            for (size_t k = 0; k < blendStacks.size(); ++k)
            {
                SBlendStackItem::SplatStack& splats = blendStacks[k].splats;
                if (!splats.empty() && splats.back().m_Texture == tex)
                {
                    CVertexBuffer::VBChunk* vertices = blendStacks[k].vertices;
                    CVertexBuffer::VBChunk* indices = blendStacks[k].indices;

                    BatchElements& batch = PooledPairGet(PooledMapGet(batches.back().m_Batches, vertices->m_Owner, arena), indices->m_Owner, arena);
                    batch.first.push_back(splats.back().m_IndexCount);

                    u8* indexBase = indices->m_Owner->GetBindAddress();
                    batch.second.push_back(indexBase + sizeof(u16)*(indices->m_Index + splats.back().m_IndexStart));

                    splats.pop_back();
                }
            }
        }

        CTerrainTextureEntry* bestTex = NULL;
        size_t bestStackSize = 0;

        for (size_t k = 0; k < blendStacks.size(); ++k)
        {
            SBlendStackItem::SplatStack& splats = blendStacks[k].splats;
            if (splats.size() > bestStackSize)
            {
                bestStackSize = splats.size();
                bestTex = splats.back().m_Texture;
            }
        }

        if (bestStackSize == 0)
            break;

        SBlendBatch layer(arena);
        layer.m_Texture = bestTex;
        batches.push_back(layer);
    }

    PROFILE_END("compute batches");

    CVertexBuffer* lastVB = NULL;

    for (BatchesStack::iterator itt = batches.begin(); itt != batches.end(); ++itt)
    {       
        if (itt->m_Texture->GetMaterial().GetSamplers().size() == 0)
            continue;
        
        int numPasses = 1;
        CShaderTechniquePtr techBase;
        
        if (!isDummyShader)
        {
            techBase = g_Renderer.GetShaderManager().LoadEffect(itt->m_Texture->GetMaterial().GetShaderEffect(), contextBlend, itt->m_Texture->GetMaterial().GetShaderDefines(0));
            
            numPasses = techBase->GetNumPasses();
        }
        
        CShaderProgramPtr previousShader;
        for (int pass = 0; pass < numPasses; ++pass)
        {
            if (!isDummyShader)
            {
                techBase->BeginPass(pass);
                TerrainRenderer::PrepareShader(techBase->GetShader(), shadow);
                
                glEnable(GL_BLEND);
                glBlendFunc(GL_SRC_ALPHA, GL_ONE_MINUS_SRC_ALPHA);
            }
                
            const CShaderProgramPtr& shader = isDummyShader ? dummy : techBase->GetShader(pass);
                
            if (itt->m_Texture)
            {
                const CMaterial::SamplersVector& samplers = itt->m_Texture->GetMaterial().GetSamplers();
                size_t samplersNum = samplers.size();
                
                for (size_t s = 0; s < samplersNum; ++s)
                {
                    const CMaterial::TextureSampler& samp = samplers[s];
                    shader->BindTexture(samp.Name, samp.Sampler);
                }

                shader->BindTexture(str_blendTex, itt->m_Texture->m_TerrainAlpha->second.m_hCompositeAlphaMap);

                itt->m_Texture->GetMaterial().GetStaticUniforms().BindUniforms(shader);
                
#if !CONFIG2_GLES
                if (isDummyShader)
                {
                    pglClientActiveTextureARB(GL_TEXTURE0);
                    glMatrixMode(GL_TEXTURE);
                    glLoadMatrixf(itt->m_Texture->GetTextureMatrix());
                    glMatrixMode(GL_MODELVIEW);
                }
                else
#endif
                {
                    float c = itt->m_Texture->GetTextureMatrix()[0];
                    float ms = itt->m_Texture->GetTextureMatrix()[8];
                    shader->Uniform(str_textureTransform, c, ms, -ms, 0.f);
                }
            }
            else
            {
                shader->BindTexture(str_baseTex, g_Renderer.GetTextureManager().GetErrorTexture());
            }

            for (VertexBufferBatches::iterator itv = itt->m_Batches.begin(); itv != itt->m_Batches.end(); ++itv)
            {
                // Rebind the VB only if it changed since the last batch
                if (itv->first != lastVB || shader != previousShader)
                {
                    lastVB = itv->first;
                    previousShader = shader;
                    GLsizei stride = sizeof(SBlendVertex);
                    SBlendVertex *base = (SBlendVertex *)itv->first->Bind();

                    shader->VertexPointer(3, GL_FLOAT, stride, &base->m_Position[0]);
                    shader->ColorPointer(4, GL_UNSIGNED_BYTE, stride, &base->m_DiffuseColor);
                    shader->NormalPointer(GL_FLOAT, stride, &base->m_Normal[0]);
                    shader->TexCoordPointer(GL_TEXTURE0, 3, GL_FLOAT, stride, &base->m_Position[0]);
                    shader->TexCoordPointer(GL_TEXTURE1, 2, GL_FLOAT, stride, &base->m_AlphaUVs[0]);
                }

                shader->AssertPointersBound();

                for (IndexBufferBatches::iterator it = itv->second.begin(); it != itv->second.end(); ++it)
                {
                    it->first->Bind();

                    BatchElements& batch = it->second;

                    if (!g_Renderer.m_SkipSubmit)
                    {
                        for (size_t i = 0; i < batch.first.size(); ++i)
                            glDrawElements(GL_TRIANGLES, batch.first[i], GL_UNSIGNED_SHORT, batch.second[i]);
                    }

                    g_Renderer.m_Stats.m_DrawCalls++;
                    g_Renderer.m_Stats.m_BlendSplats++;
                    g_Renderer.m_Stats.m_TerrainTris += std::accumulate(batch.first.begin(), batch.first.end(), 0) / 3;
                }
            }
            
            if (!isDummyShader)
            {
                glDisable(GL_BLEND);
                techBase->EndPass();
            }
        }
    }

#if !CONFIG2_GLES
    if (isDummyShader)
    {
        pglClientActiveTextureARB(GL_TEXTURE0);
        glMatrixMode(GL_TEXTURE);
        glLoadIdentity();
        glMatrixMode(GL_MODELVIEW);
    }
#endif

    CVertexBuffer::Unbind();
}

void CPatchRData::RenderStreams(const std::vector<CPatchRData*>& patches, const CShaderProgramPtr& shader, int streamflags)
{
    // Each batch has a list of index counts, and a list of pointers-to-first-indexes
    typedef std::pair<std::vector<GLint>, std::vector<void*> > BatchElements;

    // Group batches by index buffer
    typedef std::map<CVertexBuffer*, BatchElements> IndexBufferBatches;

    // Group batches by vertex buffer
    typedef std::map<CVertexBuffer*, IndexBufferBatches> VertexBufferBatches;

    VertexBufferBatches batches;

    PROFILE_START("compute batches");

    // Collect all the patches into their appropriate batches
    for (size_t i = 0; i < patches.size(); ++i)
    {
        CPatchRData* patch = patches[i];
        BatchElements& batch = batches[patch->m_VBBase->m_Owner][patch->m_VBBaseIndices->m_Owner];

        batch.first.push_back(patch->m_VBBaseIndices->m_Count);

        u8* indexBase = patch->m_VBBaseIndices->m_Owner->GetBindAddress();
        batch.second.push_back(indexBase + sizeof(u16)*(patch->m_VBBaseIndices->m_Index));
    }

    PROFILE_END("compute batches");

    ENSURE(!(streamflags & ~(STREAM_POS|STREAM_COLOR|STREAM_POSTOUV0|STREAM_POSTOUV1)));

    // Render each batch
    for (VertexBufferBatches::iterator itv = batches.begin(); itv != batches.end(); ++itv)
    {
        GLsizei stride = sizeof(SBaseVertex);
        SBaseVertex *base = (SBaseVertex *)itv->first->Bind();

        shader->VertexPointer(3, GL_FLOAT, stride, &base->m_Position);
        if (streamflags & STREAM_POSTOUV0)
            shader->TexCoordPointer(GL_TEXTURE0, 3, GL_FLOAT, stride, &base->m_Position);
        if (streamflags & STREAM_POSTOUV1)
            shader->TexCoordPointer(GL_TEXTURE1, 3, GL_FLOAT, stride, &base->m_Position);
        if (streamflags & STREAM_COLOR)
            shader->ColorPointer(4, GL_UNSIGNED_BYTE, stride, &base->m_DiffuseColor);

        shader->AssertPointersBound();

        for (IndexBufferBatches::iterator it = itv->second.begin(); it != itv->second.end(); ++it)
        {
            it->first->Bind();

            BatchElements& batch = it->second;

            if (!g_Renderer.m_SkipSubmit)
            {
                for (size_t i = 0; i < batch.first.size(); ++i)
                    glDrawElements(GL_TRIANGLES, batch.first[i], GL_UNSIGNED_SHORT, batch.second[i]);
            }

            g_Renderer.m_Stats.m_DrawCalls++;
            g_Renderer.m_Stats.m_TerrainTris += std::accumulate(batch.first.begin(), batch.first.end(), 0) / 3;
        }
    }

    CVertexBuffer::Unbind();
}

void CPatchRData::RenderOutline()
{
    CTerrain* terrain = m_Patch->m_Parent;
    ssize_t gx = m_Patch->m_X * PATCH_SIZE;
    ssize_t gz = m_Patch->m_Z * PATCH_SIZE;

    CVector3D pos;
    std::vector<CVector3D> line;

    ssize_t i, j;

    for (i = 0, j = 0; i <= PATCH_SIZE; ++i)
    {
        terrain->CalcPosition(gx + i, gz + j, pos);
        line.push_back(pos);
    }
    for (i = PATCH_SIZE, j = 1; j <= PATCH_SIZE; ++j)
    {
        terrain->CalcPosition(gx + i, gz + j, pos);
        line.push_back(pos);
    }
    for (i = PATCH_SIZE-1, j = PATCH_SIZE; i >= 0; --i)
    {
        terrain->CalcPosition(gx + i, gz + j, pos);
        line.push_back(pos);
    }
    for (i = 0, j = PATCH_SIZE-1; j >= 0; --j)
    {
        terrain->CalcPosition(gx + i, gz + j, pos);
        line.push_back(pos);
    }

#if CONFIG2_GLES
#warning TODO: implement CPatchRData::RenderOutlines for GLES
#else
    glVertexPointer(3, GL_FLOAT, sizeof(CVector3D), &line[0]);
    glDrawArrays(GL_LINE_STRIP, 0, line.size());
#endif
}

void CPatchRData::RenderSides(CShaderProgramPtr& shader)
{
    ENSURE(m_UpdateFlags==0);

    if (!m_VBSides)
        return;

    SSideVertex *base = (SSideVertex *)m_VBSides->m_Owner->Bind();

    // setup data pointers
    GLsizei stride = sizeof(SSideVertex);
    shader->VertexPointer(3, GL_FLOAT, stride, &base->m_Position);

    shader->AssertPointersBound();

    if (!g_Renderer.m_SkipSubmit)
        glDrawArrays(GL_TRIANGLE_STRIP, m_VBSides->m_Index, (GLsizei)m_VBSides->m_Count);

    // bump stats
    g_Renderer.m_Stats.m_DrawCalls++;
    g_Renderer.m_Stats.m_TerrainTris += m_VBSides->m_Count - 2;

    CVertexBuffer::Unbind();
}

void CPatchRData::RenderPriorities(CTextRenderer& textRenderer)
{
    CTerrain* terrain = m_Patch->m_Parent;
    CCamera* camera = g_Game->GetView()->GetCamera();

    for (ssize_t j = 0; j < PATCH_SIZE; ++j)
    {
        for (ssize_t i = 0; i < PATCH_SIZE; ++i)
        {
            ssize_t gx = m_Patch->m_X * PATCH_SIZE + i;
            ssize_t gz = m_Patch->m_Z * PATCH_SIZE + j;

            CVector3D pos;
            terrain->CalcPosition(gx, gz, pos);

            // Move a bit towards the center of the tile
            pos.X += TERRAIN_TILE_SIZE/4.f;
            pos.Z += TERRAIN_TILE_SIZE/4.f;

            float x, y;
            camera->GetScreenCoordinates(pos, x, y);

            textRenderer.PrintfAt(x, y, L"%d", m_Patch->m_MiniPatches[j][i].Priority);
        }
    }
}

//
// Water build and rendering
//

// Build vertex buffer for water vertices over our patch
void CPatchRData::BuildWater()
{
    PROFILE3("build water");

    // number of vertices in each direction in each patch
    ENSURE((PATCH_SIZE % water_cell_size) == 0);

    if (m_VBWater)
    {
        g_VBMan.Release(m_VBWater);
        m_VBWater = 0;
    }
    if (m_VBWaterIndices)
    {
        g_VBMan.Release(m_VBWaterIndices);
        m_VBWaterIndices = 0;
    }
    m_WaterBounds.SetEmpty();

    // We need to use this to access the water manager or we may not have the
    // actual values but some compiled-in defaults
    CmpPtr<ICmpWaterManager> cmpWaterManager(*m_Simulation, SYSTEM_ENTITY);
    if (!cmpWaterManager)
        return;
    
    // Build data for water
    std::vector<SWaterVertex> water_vertex_data;
    std::vector<GLushort> water_indices;
    u16 water_index_map[PATCH_SIZE+1][PATCH_SIZE+1];
    memset(water_index_map, 0xFF, sizeof(water_index_map));

    // TODO: This is not (yet) exported via the ICmp interface so... we stick to these values which can be compiled in defaults
    WaterManager* WaterMgr = g_Renderer.GetWaterManager();

    if (WaterMgr->m_NeedInfoUpdate)
    {
        WaterMgr->m_NeedInfoUpdate = false;
        WaterMgr->CreateSuperfancyInfo(m_Simulation);
    }
    CPatch* patch = m_Patch;
    CTerrain* terrain = patch->m_Parent;

    ssize_t mapSize = (size_t)terrain->GetVerticesPerSide();

    ssize_t x1 = m_Patch->m_X*PATCH_SIZE;
    ssize_t z1 = m_Patch->m_Z*PATCH_SIZE;

    // build vertices, uv, and shader varying
    for (ssize_t z = 0; z < PATCH_SIZE; z += water_cell_size)
    {
        for (ssize_t x = 0; x <= PATCH_SIZE; x += water_cell_size)
        {
            // Check that the edge at x is partially underwater
            float startTerrainHeight[2] = { terrain->GetVertexGroundLevel(x+x1, z+z1), terrain->GetVertexGroundLevel(x+x1, z+z1 + water_cell_size) };
            float startWaterHeight[2] = { cmpWaterManager->GetExactWaterLevel(x+x1, z+z1), cmpWaterManager->GetExactWaterLevel(x+x1, z+z1 + water_cell_size) };
            if (startTerrainHeight[0] >= startWaterHeight[0] && startTerrainHeight[1] >= startWaterHeight[1])
                continue;

            // Move x back one cell (unless at start of patch), then scan rightwards
            bool belowWater = true;
            ssize_t stripStart;
            for (stripStart = x = std::max(x-water_cell_size, (ssize_t)0); x <= PATCH_SIZE; x += water_cell_size)
            {
                // If this edge is not underwater, and neither is the previous edge
                // (i.e. belowWater == false), then stop this strip since we've reached
                // a cell that's entirely above water
                float terrainHeight[2] = { terrain->GetVertexGroundLevel(x+x1, z+z1), terrain->GetVertexGroundLevel(x+x1, z+z1 + water_cell_size) };
                float waterHeight[2] = { cmpWaterManager->GetExactWaterLevel(x+x1, z+z1), cmpWaterManager->GetExactWaterLevel(x+x1, z+z1 + water_cell_size) };
                if (terrainHeight[0] >= waterHeight[0] && terrainHeight[1] >= waterHeight[1])
                {
                    if (!belowWater)
                        break;
                    belowWater = false;
                }
                else
                    belowWater = true;

                // Edge (x,z)-(x,z+1) is at least partially underwater, so extend the water plane strip across it

                // Compute vertex data for the 2 points on the edge
                for (int j = 0; j < 2; j++)
                {
                    // Check if we already computed this vertex from an earlier strip
                    if (water_index_map[z+j*water_cell_size][x] != 0xFFFF)
                        continue;

                    SWaterVertex vertex;

                    terrain->CalcPosition(x+x1, z+z1 + j*water_cell_size, vertex.m_Position);
                    float depth = waterHeight[j] - vertex.m_Position.Y;
                    vertex.m_Position.Y = waterHeight[j];
                    m_WaterBounds += vertex.m_Position;

                    // NB: Usually this factor is view dependent, but for performance reasons
                    // we do not take it into account with basic non-shader based water.
                    // Average constant Fresnel effect for non-fancy water
                    float alpha = clamp(depth / WaterMgr->m_WaterFullDepth + WaterMgr->m_WaterAlphaOffset, WaterMgr->m_WaterAlphaOffset, WaterMgr->m_WaterMaxAlpha);

                    // Split the depth data across 24 bits, so the fancy-water shader can reconstruct
                    // the depth value while the simple-water can just use the precomputed alpha
                    float depthInt = floor(depth);
                    float depthFrac = depth - depthInt;
                    vertex.m_DepthData = SColor4ub(
                        u8(clamp(depthInt, 0.0f, 255.0f)),
                        u8(clamp(-depthInt, 0.0f, 255.0f)),
                        u8(clamp(depthFrac*255.0f, 0.0f, 255.0f)),
                        u8(clamp(alpha*255.0f, 0.0f, 255.0f)));

                    int tx = x+x1;
                    int ty = z+z1 + j*water_cell_size;

                    vertex.m_WaterData = CVector4D(WaterMgr->m_WaveX[tx + ty*mapSize],
                                                   WaterMgr->m_WaveZ[tx + ty*mapSize],
                                                   WaterMgr->m_DistanceToShore[tx + ty*mapSize],
                                                   WaterMgr->m_FoamFactor[tx + ty*mapSize]);

                    water_index_map[z+j*water_cell_size][x] = water_vertex_data.size();
                    water_vertex_data.push_back(vertex);
                }

                // If this was not the first x in the strip, then add a quad
                // using the computed vertex data

                if (x <= stripStart)
                    continue;

                water_indices.push_back(water_index_map[z + water_cell_size][x - water_cell_size]);
                water_indices.push_back(water_index_map[z][x - water_cell_size]);
                water_indices.push_back(water_index_map[z][x]);
                water_indices.push_back(water_index_map[z + water_cell_size][x]);
            }
        }
    }

    // no vertex buffers if no data generated
    if (water_indices.size() == 0)
        return;

    // allocate vertex buffer
    m_VBWater = g_VBMan.Allocate(sizeof(SWaterVertex), water_vertex_data.size(), GL_STATIC_DRAW, GL_ARRAY_BUFFER);
    m_VBWater->m_Owner->UpdateChunkVertices(m_VBWater, &water_vertex_data[0]);

    // Construct indices buffer
    m_VBWaterIndices = g_VBMan.Allocate(sizeof(GLushort), water_indices.size(), GL_STATIC_DRAW, GL_ELEMENT_ARRAY_BUFFER);
    m_VBWaterIndices->m_Owner->UpdateChunkVertices(m_VBWaterIndices, &water_indices[0]);
}

void CPatchRData::RenderWater(CShaderProgramPtr& shader)
{
    ASSERT(m_UpdateFlags==0);

    if (!m_VBWater)
        return;

    SWaterVertex *base=(SWaterVertex *)m_VBWater->m_Owner->Bind();

    // setup data pointers
    GLsizei stride = sizeof(SWaterVertex);
    shader->ColorPointer(4, GL_UNSIGNED_BYTE, stride, &base[m_VBWater->m_Index].m_DepthData);
    shader->VertexPointer(3, GL_FLOAT, stride, &base[m_VBWater->m_Index].m_Position);
    shader->TexCoordPointer(GL_TEXTURE0, 4, GL_FLOAT, stride, &base[m_VBWater->m_Index].m_WaterData);

    shader->AssertPointersBound();

    // render
    if (!g_Renderer.m_SkipSubmit)
    {
        u8* indexBase = m_VBWaterIndices->m_Owner->Bind();
#if CONFIG2_GLES
#warning TODO: fix CPatchRData::RenderWater for GLES (avoid GL_QUADS)
#else
        glDrawElements(GL_QUADS, (GLsizei) m_VBWaterIndices->m_Count,
            GL_UNSIGNED_SHORT, indexBase + sizeof(u16)*(m_VBWaterIndices->m_Index));
#endif
    }

    // bump stats
    g_Renderer.m_Stats.m_DrawCalls++;
    g_Renderer.m_Stats.m_WaterTris += m_VBWaterIndices->m_Count / 2;

    CVertexBuffer::Unbind();
}