impostor.cpp

大型多人在线游戏开发,该书光盘上附带的源码

/*
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Copyright (c) 2000, Sean O'Neil
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*/

#include "Master.h"
#include "GameApp.h"
#include "Impostor.h"

float CImpostor::CalculateError(C3DObject *pCamera)
{
	CVector vOffset = m_vCamera - pCamera->GetPosition();
	return vOffset.Magnitude();
}

bool CImpostor::IsInView(C3DObject *pCamera)
{
	// Create the 8 corner vertices of the model's 3D bounding box
	CVector vCorner[8];
	vCorner[0] = CVector(m_vDimension.x, m_vDimension.y, m_vDimension.z);
	vCorner[1] = CVector(m_vDimension.x, m_vDimension.y, -m_vDimension.z);
	vCorner[2] = CVector(m_vDimension.x, -m_vDimension.y, -m_vDimension.z);
	vCorner[3] = CVector(m_vDimension.x, -m_vDimension.y, m_vDimension.z);
	vCorner[4] = CVector(-m_vDimension.x, m_vDimension.y, m_vDimension.z);
	vCorner[5] = CVector(-m_vDimension.x, m_vDimension.y, -m_vDimension.z);
	vCorner[6] = CVector(-m_vDimension.x, -m_vDimension.y, -m_vDimension.z);
	vCorner[7] = CVector(-m_vDimension.x, -m_vDimension.y, m_vDimension.z);

	// Calculate the camera model-view matrix for testing the bounding box
	CVector v = m_vPosition - pCamera->GetPosition();
	CMatrix mView = pCamera->GetViewMatrix();
	CMatrix mModel;
	mModel.ModelMatrix(*this, v);
	CMatrix mCamera = mView * mModel;

	CVector vActual;
	for(int i=0; i<8; i++)
	{
		// Transform each corner vertex and divide by -z (equivalent to 90 degree fov projection)
		// This will help us find the 2D bounding box we need to fit around our impostor
		vActual = mCamera.TransformVector(vCorner[i]);
		if(vActual.z < 0)
		{
			vActual.x /= -vActual.z;
			vActual.y /= -vActual.z;
			if(Abs(vActual.x) < 1 && Abs(vActual.y) < 1)
				return true;
		}
	}
	return false;
}

void CImpostor::InitImpostorRender(C3DObject *pCamera)
{
	// Create the 8 corner vertices of the model's 3D bounding box
	CVector vCorner[8];
	vCorner[0] = CVector(m_vDimension.x, m_vDimension.y, m_vDimension.z);
	vCorner[1] = CVector(m_vDimension.x, m_vDimension.y, -m_vDimension.z);
	vCorner[2] = CVector(m_vDimension.x, -m_vDimension.y, -m_vDimension.z);
	vCorner[3] = CVector(m_vDimension.x, -m_vDimension.y, m_vDimension.z);
	vCorner[4] = CVector(-m_vDimension.x, m_vDimension.y, m_vDimension.z);
	vCorner[5] = CVector(-m_vDimension.x, m_vDimension.y, -m_vDimension.z);
	vCorner[6] = CVector(-m_vDimension.x, -m_vDimension.y, -m_vDimension.z);
	vCorner[7] = CVector(-m_vDimension.x, -m_vDimension.y, m_vDimension.z);

	// Calculate the impostor model-view matrix so we can find the 2D bounding box for the billboard texture
	// Currently the up vector is arbitrary. It is chosen in such a way that it can't be parallel to the view vector.
	// (We can optimize impostor resolution by picking a better up vector, but we'd have to be careful that it is always perpendicular to the view vector.)
	CVector v = m_vPosition - pCamera->GetPosition();
	CMatrix mModel, mView;
	mModel.ModelMatrix(*this, v);
	mView.ViewMatrix(CVector(0.0f), v, CVector(v.y, -v.z, v.x));
	m_vUp = CVector(mView.f12, mView.f22, mView.f32);
	CMatrix m = mView * mModel;

	m_fMinx = 1; m_fMiny = 1; m_fMaxx = -1; m_fMaxy = -1;
	for(int i=0; i<8; i++)
	{
		// Transform each corner vertex and divide by -z (equivalent to 90 degree fov projection)
		// This will help us find the 2D bounding box we need to fit around our impostor
		vCorner[i] = m.TransformVector(vCorner[i]);
		vCorner[i] /= -vCorner[i].z;
		m_fMinx = Min(m_fMinx, vCorner[i].x);
		m_fMiny = Min(m_fMiny, vCorner[i].y);
		m_fMaxx = Max(m_fMaxx, vCorner[i].x);
		m_fMaxy = Max(m_fMaxy, vCorner[i].y);
	}

	// Use the size of the bounding box to determine the resolution we need for the impostor
	float fTemp = Max(m_fMaxx-m_fMinx, m_fMaxy-m_fMiny) * 0.5f;

	// If it goes too far past the boundaries of the screen, handle it as a special case
	m_vOffset = CVector(0.0f);
	if(fTemp > 1.0f)
	{
		// When really close to the impostor, these numbers tend to approach infinity. We need to do something to address that
		float fDist = Max(v.Magnitude(), 32);
		m_fMinx = -fDist;
		m_fMaxx = fDist;
		m_fMiny = -fDist;
		m_fMaxy = fDist;
		m_nResolution = 256;
		m_vUp = pCamera->GetUpAxis();

		m_vOffset = GetPosition() - (pCamera->GetPosition() + pCamera->GetViewAxis()*fDist);

		glViewport(0, 0, m_nResolution, m_nResolution);
		glMatrixMode(GL_MODELVIEW);
		glPushMatrix();
		v = m_vPosition - pCamera->GetPosition();
		CMatrix mView = pCamera->GetViewMatrix();
		CMatrix mModel;
		mModel.ModelMatrix(*this, v);
		CMatrix mCamera = mView * mModel;
		glLoadMatrixf(mCamera);
		glMatrixMode(GL_PROJECTION);
		glPushMatrix();
		glLoadIdentity();
		glFrustum(-1.0f, 1.0f, -1.0f, 1.0f, 1.0, 1000.0);
		return;
	}

	if(fTemp > 0.75f)
		m_nResolution = 256;
	else if(fTemp > 0.25f)
		m_nResolution = 128;
	else if(fTemp > 0.1f)
		m_nResolution = 64;
	else
		m_nResolution = 32;

	// Set up the necessary viewport, modelview matrix, and projection matrix for rendering to the impostor texture
	glViewport(0, 0, m_nResolution, m_nResolution);
	glMatrixMode(GL_MODELVIEW);
	glPushMatrix();
	glLoadMatrixf(m);
	glMatrixMode(GL_PROJECTION);
	glPushMatrix();
	glLoadIdentity();
	glFrustum(m_fMinx, m_fMaxx, m_fMiny, m_fMaxy, 1.0, 1000.0);

	// Scale these up by distance so they can be used to determine billboard vertices
	float fDist = v.Magnitude();
	m_fMinx *= fDist;
	m_fMiny *= fDist;
	m_fMaxx *= fDist;
	m_fMaxy *= fDist;
}

void CImpostor::FinishImpostorRender()
{
	// Copy the currently rendered viewport into the impostor texture
	m_tImpostor.InitCopy(0, 0, m_nResolution, m_nResolution);

	// Clean up the OpenGL matrix stack and viewport
	glMatrixMode(GL_PROJECTION);
	glPopMatrix();
	glMatrixMode(GL_MODELVIEW);
	glPopMatrix();
	glViewport(0, 0, GetGameApp()->GetWidth(), GetGameApp()->GetHeight());
}

void CImpostor::Draw(C3DObject *pCamera)
{
	// First determine the actual normal, up, and right vectors for the billboard
	CVector vPos = (m_vPosition - m_vOffset) - pCamera->GetPosition();
	float fDistance = vPos.Magnitude();
	CVector vNormal = vPos / -fDistance;
	CVector vRight = m_vUp ^ vNormal;
	vRight.Normalize();
	CVector vUp = vNormal ^ vRight;
	vUp.Normalize();

	// Then draw the billboarded rectangle
	m_tImpostor.Enable();
	glBlendFunc(GL_ONE, GL_ONE_MINUS_SRC_ALPHA);
	glEnable(GL_BLEND);
	glBegin(GL_QUADS);
	glTexCoord2f(0, 1);
	glVertex3fv(vPos + vUp*m_fMaxy + vRight*m_fMinx);
	glTexCoord2f(0, 0);
	glVertex3fv(vPos + vUp*m_fMiny + vRight*m_fMinx);
	glTexCoord2f(1, 0);
	glVertex3fv(vPos + vUp*m_fMiny + vRight*m_fMaxx);
	glTexCoord2f(1, 1);
	glVertex3fv(vPos + vUp*m_fMaxy + vRight*m_fMaxx);
	glEnd();
	glDisable(GL_BLEND);
	m_tImpostor.Disable();
}