/*
-----------------------------------------------------------------------------
This source file is part of OGRE
    (Object-oriented Graphics Rendering Engine)
For the latest info, see http://www.ogre3d.org/

Copyright © 2000-2003 The OGRE Team
Also see acknowledgements in Readme.html

You may use this sample code for anything you like, it is not covered by the
LGPL like the rest of the engine.
-----------------------------------------------------------------------------
*/


#include "WaterMesh.h"

#define ANIMATIONS_PER_SECOND 100.0f

WaterMesh::WaterMesh(const String& meshName, Real planeSize, int complexity)
{
	int x,y,b; // I prefer to initialize for() variables inside it, but VC doesn't like it ;(
	
	this->meshName = meshName ;
	this->complexity =  complexity ;
	numFaces = 2 * complexity * complexity; 
	numVertices = (complexity + 1) * (complexity + 1) ;
	lastTimeStamp = 0 ;
	lastAnimationTimeStamp = 0;
	lastFrameTime = 0 ;
	
	// initialize algorithm parameters
	PARAM_C = 0.3f ; // ripple speed 
	PARAM_D = 0.4f ; // distance
	PARAM_U = 0.05f ; // viscosity
	PARAM_T = 0.13f ; // time
	useFakeNormals = false ;
	
	// allocate space for normal calculation
	vNormals = new Vector3[numVertices];
	
	// create mesh and submesh
	mesh= (Mesh*) MeshManager::getSingleton().createManual(meshName) ;
	subMesh = mesh->createSubMesh();
	subMesh->useSharedVertices=false;
	
	// Vertex buffers
	subMesh->vertexData = new VertexData();
	subMesh->vertexData->vertexStart = 0;
	subMesh->vertexData->vertexCount = numVertices;

	VertexDeclaration* vdecl = subMesh->vertexData->vertexDeclaration; 
	VertexBufferBinding* vbind = subMesh->vertexData->vertexBufferBinding;
	

	vdecl->addElement(0, 0, VET_FLOAT3, VES_POSITION);
	vdecl->addElement(1, 0, VET_FLOAT3, VES_NORMAL);
	vdecl->addElement(2, 0, VET_FLOAT2, VES_TEXTURE_COORDINATES);
	
	// Prepare buffer for positions - todo: first attempt, slow
	posVertexBuffer = 
         HardwareBufferManager::getSingleton().createVertexBuffer( 
            3*sizeof(Real), 
			numVertices, 
			HardwareBuffer::HBU_DYNAMIC_WRITE_ONLY_DISCARDABLE);
	vbind->setBinding(0, posVertexBuffer);

	// Prepare buffer for normals - write only
	normVertexBuffer = 
         HardwareBufferManager::getSingleton().createVertexBuffer( 
            3*sizeof(Real), 
			numVertices, 
			HardwareBuffer::HBU_DYNAMIC_WRITE_ONLY_DISCARDABLE);
	vbind->setBinding(1, normVertexBuffer);
	
	// Prepare texture coords buffer - static one
	// todo: optimize to write directly into buffer
	Real *texcoordsBufData = new Real[numVertices*2];
	for(y=0;y<=complexity;y++) {
		for(x=0;x<=complexity;x++) {
			texcoordsBufData[2*(y*(complexity+1)+x)+0] = (float)x / complexity ;
			texcoordsBufData[2*(y*(complexity+1)+x)+1] = 1.0f - ((float)y / (complexity)) ;
		}
	}
	texcoordsVertexBuffer = 
         HardwareBufferManager::getSingleton().createVertexBuffer( 
            2*sizeof(Real), 
			numVertices, 
			HardwareBuffer::HBU_STATIC_WRITE_ONLY); 
	texcoordsVertexBuffer->writeData(0, 
		texcoordsVertexBuffer->getSizeInBytes(),
		texcoordsBufData,
		true); // true?
	delete [] texcoordsBufData;
    vbind->setBinding(2, texcoordsVertexBuffer); 
	
	// Prepare buffer for indices
	indexBuffer = 
		HardwareBufferManager::getSingleton().createIndexBuffer(
			HardwareIndexBuffer::IT_16BIT, 
			3*numFaces, 
			HardwareBuffer::HBU_STATIC, true);
	unsigned short *faceVertexIndices = (unsigned short*) 
		indexBuffer->lock(0, numFaces*3*2, HardwareBuffer::HBL_DISCARD);
	for(y=0 ; y<complexity ; y++) {
		for(int x=0 ; x<complexity ; x++) {
			unsigned short *twoface = faceVertexIndices + (y*complexity+x)*2*3;
			int p0 = y*(complexity+1) + x ;
			int p1 = y*(complexity+1) + x + 1 ;
			int p2 = (y+1)*(complexity+1) + x ;
			int p3 = (y+1)*(complexity+1) + x + 1 ;
			twoface[0]=p2; //first tri
			twoface[1]=p1;
			twoface[2]=p0;
			twoface[3]=p2; //second tri
			twoface[4]=p3;
			twoface[5]=p1;
		}
	}
	indexBuffer->unlock();
	// Set index buffer for this submesh
	subMesh->indexData->indexBuffer = indexBuffer;
	subMesh->indexData->indexStart = 0;
	subMesh->indexData->indexCount = 3*numFaces;
	
	/*	prepare vertex positions
	 *	note - we use 3 vertex buffers, since algorighm uses two last phases 
	 *	to calculate the next one
	 */
	for(b=0;b<3;b++) {
		vertexBuffers[b] = new Real[numVertices * 3] ;
		for(y=0;y<=complexity;y++) {
			for(x=0;x<=complexity;x++) {
				int numPoint = y*(complexity+1) + x ;
				Real* vertex = vertexBuffers[b] + 3*numPoint ;
				vertex[0]=(float)(x) / (float)(complexity) * (float) planeSize ;
				vertex[1]= 0 ; // rand() % 30 ;
				vertex[2]=(float)(y) / (float)(complexity) * (float) planeSize ;
			}
		}
	}
	
	AxisAlignedBox meshBounds(0,0,0,
		planeSize,0, planeSize);
	mesh->_setBounds(meshBounds);
	
	currentBuffNumber = 0 ;
	posVertexBuffer->writeData(0, 
		posVertexBuffer->getSizeInBytes(), // size 
		vertexBuffers[currentBuffNumber], // source
		true); // discard?

    mesh->load();
    mesh->touch();
}
/* ========================================================================= */
WaterMesh::~WaterMesh ()
{
 	delete[] vertexBuffers[0];
 	delete[] vertexBuffers[1];
 	delete[] vertexBuffers[2];

	delete[] vNormals;
}
/* ========================================================================= */
void WaterMesh::push(Real x, Real y, Real depth, bool absolute)
{
	Real *buf = vertexBuffers[currentBuffNumber]+1 ;
	// scale pressure according to time passed
	depth = depth * lastFrameTime * ANIMATIONS_PER_SECOND ;
#define _PREP(addx,addy) { \
	Real *vertex=buf+3*((int)(y+addy)*(complexity+1)+(int)(x+addx)) ; \
	Real diffy = y - floor(y+addy); \
	Real diffx = x - floor(x+addx); \
	Real dist=sqrt(diffy*diffy + diffx*diffx) ; \
	Real power = 1 - dist ; \
	if (power<0)  \
		power = 0; \
	if (absolute) \
		*vertex = depth*power ;  \
	else \
		*vertex += depth*power ;  \
} /* #define */
	_PREP(0,0);
	_PREP(0,1);
	_PREP(1,0);
	_PREP(1,1);
#undef _PREP	
}
/* ========================================================================= */
Real WaterMesh::getHeight(Real x, Real y)
{
#define hat(_x,_y) buf[3*((int)_y*(complexity+1)+(int)(_x))]
	Real *buf = vertexBuffers[currentBuffNumber] ;
	Real xa = floor(x);
	Real xb = xa + 1 ;
	Real ya = floor(y);
	Real yb = ya + 1 ;
	Real *vertex = buf + 3*((int)(ya)*(complexity+1)+(int)(xa));
	Real yaxavg = hat(xa,ya) * (1.0f-fabs(xa-x)) + hat(xb,ya) * (1.0f-fabs(xb-x));
	Real ybxavg = hat(xa,yb) * (1.0f-fabs(xa-x)) + hat(xb,yb) * (1.0f-fabs(xb-x));
	Real yavg = yaxavg * (1.0f-fabs(ya-y)) + ybxavg * (1.0f-fabs(yb-y)) ;
	return yavg ;
}
/* ========================================================================= */
void WaterMesh::calculateFakeNormals()
{
	int x,y;
	Real *buf = vertexBuffers[currentBuffNumber] + 1;
	Real *pNormals = (Real*) normVertexBuffer->lock(
		0,normVertexBuffer->getSizeInBytes(), HardwareBuffer::HBL_DISCARD);
	for(y=1;y<complexity;y++) {
		Real *nrow = pNormals + 3*y*(complexity+1);
		Real *row = buf + 3*y*(complexity+1) ;
		Real *rowup = buf + 3*(y-1)*(complexity+1) ;
		Real *rowdown = buf + 3*(y+1)*(complexity+1) ;
		for(x=1;x<complexity;x++) {
			Real xdiff = row[3*x+3] - row[3*x-3] ;
			Real ydiff = rowup[3*x] - rowdown[3*x-3] ;
			Vector3 norm(xdiff,30,ydiff);
			norm.normalise();
			nrow[3*x+0] = norm.x;
			nrow[3*x+1] = norm.y;
			nrow[3*x+2] = norm.z;
		}
	}
	normVertexBuffer->unlock();
}
/* ========================================================================= */
void WaterMesh::calculateNormals()
{
	int i,x,y;
	Real *buf = vertexBuffers[currentBuffNumber] + 1;
	// zero normals
	for(i=0;i<numVertices;i++) {
		vNormals[i] = Vector3::ZERO;
	}
	// first, calculate normals for faces, add them to proper vertices
	buf = vertexBuffers[currentBuffNumber] ;
	unsigned short* vinds = (unsigned short*) indexBuffer->lock(
		0, indexBuffer->getSizeInBytes(), HardwareBuffer::HBL_READ_ONLY);
	Real *pNormals = (Real*) normVertexBuffer->lock(
		0, normVertexBuffer->getSizeInBytes(), HardwareBuffer::HBL_DISCARD);
	for(i=0;i<numFaces;i++) {
		int p0 = vinds[3*i] ;
		int p1 = vinds[3*i+1] ;
		int p2 = vinds[3*i+2] ;
		Vector3 v0(buf[3*p0], buf[3*p0+1], buf[3*p0+2]);
		Vector3 v1(buf[3*p1], buf[3*p1+1], buf[3*p1+2]);
		Vector3 v2(buf[3*p2], buf[3*p2+1], buf[3*p2+2]);
		Vector3 diff1 = v2 - v1 ;
		Vector3 diff2 = v0 - v1 ;
		Vector3 fn = diff1.crossProduct(diff2);
		vNormals[p0] += fn ;
		vNormals[p1] += fn ;
		vNormals[p2] += fn ;
	}
	// now normalize vertex normals
	for(y=0;y<=complexity;y++) {
		for(x=0;x<=complexity;x++) {
			int numPoint = y*(complexity+1) + x ;
			Vector3 n = vNormals[numPoint] ;
			n.normalise() ;
			Real* normal = pNormals + 3*numPoint ;
			normal[0]=n.x;
			normal[1]=n.y;
			normal[2]=n.z;
		}
	}
	indexBuffer->unlock();
	normVertexBuffer->unlock();
}
/* ========================================================================= */
void WaterMesh::updateMesh(Real timeSinceLastFrame)
{
	int x, y ;
	
	lastFrameTime = timeSinceLastFrame ;
	lastTimeStamp += timeSinceLastFrame ;
	
	// do rendering to get ANIMATIONS_PER_SECOND
	while(lastAnimationTimeStamp <= lastTimeStamp) {
	
		// switch buffer numbers
		currentBuffNumber = (currentBuffNumber + 1) % 3 ;
		Real *buf = vertexBuffers[currentBuffNumber] + 1 ; // +1 for Y coordinate
		Real *buf1 = vertexBuffers[(currentBuffNumber+2)%3] + 1 ; 
		Real *buf2 = vertexBuffers[(currentBuffNumber+1)%3] + 1; 	
	
		/* we use an algorithm from
		 * http://collective.valve-erc.com/index.php?go=water_simulation
		 * The params could be dynamically changed every frame ofcourse
		 */
		double C = PARAM_C; // ripple speed 
		double D = PARAM_D; // distance
		double U = PARAM_U; // viscosity
		double T = PARAM_T; // time
		Real TERM1 = ( 4.0f - 8.0f*C*C*T*T/(D*D) ) / (U*T+2) ;
		Real TERM2 = ( U*T-2.0f ) / (U*T+2.0f) ;
		Real TERM3 = ( 2.0f * C*C*T*T/(D*D) ) / (U*T+2) ;
		for(y=1;y<complexity;y++) { // don't do anything with border values
			Real *row = buf + 3*y*(complexity+1) ;
			Real *row1 = buf1 + 3*y*(complexity+1) ;
			Real *row1up = buf1 + 3*(y-1)*(complexity+1) ;
			Real *row1down = buf1 + 3*(y+1)*(complexity+1) ;
			Real *row2 = buf2 + 3*y*(complexity+1) ;
			for(x=1;x<complexity;x++) {
				row[3*x] = TERM1 * row1[3*x] 
					+ TERM2 * row2[3*x]
					+ TERM3 * ( row1[3*x-3] + row1[3*x+3] + row1up[3*x]+row1down[3*x] ) ;
			}
		}
		
		lastAnimationTimeStamp += (1.0f / ANIMATIONS_PER_SECOND);
	}

	if (useFakeNormals) {
		calculateFakeNormals();
	} else {
		calculateNormals();
	}

	// set vertex buffer
	posVertexBuffer->writeData(0, 
		posVertexBuffer->getSizeInBytes(), // size 
		vertexBuffers[currentBuffNumber], // source
		true); // discard?
}
