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game/client/c_tracer.cpp

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+//========= Copyright Valve Corporation, All rights reserved. ============//
+//
+// Purpose: 
+//
+// $NoKeywords: $
+//
+//=============================================================================//
+#include "cbase.h"
+#include "particledraw.h"
+#include "materialsystem/imesh.h"
+
+// memdbgon must be the last include file in a .cpp file!!!
+#include "tier0/memdbgon.h"
+
+//-----------------------------------------------------------------------------
+// Sees if the tracer is behind the camera or should be culled
+//-----------------------------------------------------------------------------
+
+static bool ClipTracer( const Vector &start, const Vector &delta, Vector &clippedStart, Vector &clippedDelta )
+{
+	// dist1 = start dot forward - origin dot forward
+	// dist2 = (start + delta ) dot forward - origin dot forward
+	// in camera space this is -start[2] since origin = 0 and vecForward = (0, 0, -1)
+	float dist1 = -start[2];
+	float dist2 = dist1 - delta[2];
+	
+	// Clipped, skip this tracer
+	if ( dist1 <= 0 && dist2 <= 0 )
+		return true;
+
+	clippedStart = start;
+	clippedDelta = delta;
+	
+	// Needs to be clipped
+	if ( dist1 <= 0 || dist2 <= 0 )
+	{
+		float fraction = dist2 - dist1;
+
+		// Too close to clipping plane
+		if ( fraction < 1e-3 && fraction > -1e-3 )
+			return true;
+
+		fraction = -dist1 / fraction;
+
+		if ( dist1 <= 0 )
+		{
+			VectorMA( start, fraction, delta, clippedStart );
+		}
+		else
+		{
+			VectorMultiply( delta, fraction, clippedDelta );
+		}
+	}
+
+	return false;
+}
+
+
+//-----------------------------------------------------------------------------
+// Computes the four verts to draw the tracer with
+//-----------------------------------------------------------------------------
+bool Tracer_ComputeVerts( const Vector &start, const Vector &delta, float width, Vector *pVerts )
+{
+	Vector clippedStart, clippedDelta;
+
+	// Clip the tracer
+	if ( ClipTracer( start, delta, clippedStart, clippedDelta ) )
+		return false;
+
+	// Figure out direction in camera space of the normal
+	Vector normal;
+	CrossProduct( clippedDelta, clippedStart, normal );
+					  
+	// don't draw if they are parallel
+	float sqLength = DotProduct( normal, normal );
+	if (sqLength < 1e-3)
+		return false;
+
+	// Resize the normal to be appropriate based on the width
+	VectorScale( normal, 0.5f * width / sqrt(sqLength), normal );
+
+	VectorSubtract( clippedStart, normal, pVerts[0] );
+	VectorAdd( clippedStart, normal, pVerts[1] );
+
+	VectorAdd( pVerts[0], clippedDelta, pVerts[2] );
+	VectorAdd( pVerts[1], clippedDelta, pVerts[3] );
+
+	return true;
+}
+
+
+void Tracer_Draw( CMeshBuilder *pMeshBuilder, Vector& start, Vector& delta, float width, float* color, float startV, float endV )
+{
+	// Clip the tracer
+	Vector verts[4];
+	if (!Tracer_ComputeVerts( start, delta, width, verts ))
+		return;
+
+	// NOTE: Gotta get the winding right so it's not backface culled
+	// (we need to turn of backface culling for these bad boys)
+	pMeshBuilder->Position3f( verts[0].x, verts[0].y, verts[0].z );
+	pMeshBuilder->TexCoord2f( 0, 0.0f, startV );
+	if (color)
+	{
+		pMeshBuilder->Color4fv( color );
+	}
+	else
+	{
+		pMeshBuilder->Color4ub( 255, 255, 255, 255 );
+	}
+	pMeshBuilder->AdvanceVertex();
+
+	pMeshBuilder->Position3f( verts[1].x, verts[1].y, verts[1].z );
+	pMeshBuilder->TexCoord2f( 0, 1.0f, startV );
+	if (color)
+	{
+		pMeshBuilder->Color4fv( color );
+	}
+	else
+	{
+		pMeshBuilder->Color4ub( 255, 255, 255, 255 );
+	}
+	pMeshBuilder->AdvanceVertex();
+
+	pMeshBuilder->Position3f( verts[3].x, verts[3].y, verts[3].z );
+	pMeshBuilder->TexCoord2f( 0, 1.0f, endV );
+	if (color)
+		pMeshBuilder->Color4fv( color );
+	else
+		pMeshBuilder->Color4ub( 255, 255, 255, 255 );
+	pMeshBuilder->AdvanceVertex();
+
+	pMeshBuilder->Position3f( verts[2].x, verts[2].y, verts[2].z );
+	pMeshBuilder->TexCoord2f( 0, 0.0f, endV );
+	if (color)
+		pMeshBuilder->Color4fv( color );
+	else
+		pMeshBuilder->Color4ub( 255, 255, 255, 255 );
+	pMeshBuilder->AdvanceVertex();
+}
+
+
+//-----------------------------------------------------------------------------
+// draw a tracer.
+//-----------------------------------------------------------------------------
+void Tracer_Draw( ParticleDraw* pDraw, Vector& start, Vector& delta, float width, float* color, float startV, float endV )
+{
+	if( !pDraw->GetMeshBuilder() )
+		return;
+
+	Tracer_Draw( pDraw->GetMeshBuilder(), start, delta, width, color, startV, endV );
+}