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Help With Vector Math

General and Gameplay Programming Programming

Started by NickGravelyn April 02, 2006 11:39 AM

3 comments, last by _goat 18 years ago

NickGravelyn

855

Author

April 02, 2006 11:39 AM

I'm writing up a camera class today and I'm having troubles. The mouse handles perfectly fine, but motion is not so good looking. I believe it may have to do with my vector math functions. Is there anything wrong here? SimStructs.h


typedef struct SimVector
{
    float x, y, z;

    void operator= (SimVector v)
    {
        x = v.x;
        y = v.y;
        z = v.z;
    }

    void operator+= (SimVector v)
    {
        x += v.x;
        y += v.y;
        z += v.z;
    }

    void operator-= (SimVector v)
    {
        x -= v.x;
        y -= v.y;
        z -= v.z;
    }

    void operator*= (float a)
    {
        x *= a;
        y *= a;
        z *= a;
    }

    void operator/= (float a)
    {
        x /= a;
        y /= a;
        z /= a;
    }

    SimVector operator+ (SimVector v)
    {
        SimVector ret;
        ret.x = x + v.x;
        ret.y = y + v.y;
        ret.z = z + v.z;
        return ret;
    }

    SimVector operator- (SimVector v)
    {
        SimVector ret;
        ret.x = x - v.x;
        ret.y = y - v.y;
        ret.z = z - v.z;
        return ret;
    }

    SimVector operator* (float a)
    {
        SimVector ret;
        ret.x = x * a;
        ret.y = y * a;
        ret.z = z * a;
    }

    SimVector operator/ (float a)
    {
        SimVector ret;
        ret.x = x / a;
        ret.y = y / a;
        ret.z = z / a;
        return ret;
    }

    float operator[] (int a)
    {
        if(a == 0)
            return x;
        if(a == 1)
            return y;
        if(a == 2)
            return z;
    }
};

namespace SimStructs
{
    float GetMagnitude(SimVector v);
    void Normalize(SimVector &v);
    float DotProduct(SimVector v1, SimVector v2);
    SimVector CrossProduct(SimVector v1, SimVector v2);
}

SimStructs.cpp


float SimStructs::GetMagnitude(SimVector v)
{
    return sqrt(v.x * v.x + v.y * v.y + v.z * v.z);
}

void SimStructs::Normalize(SimVector &v)
{
    float mag = 1.0f / SimStructs::GetMagnitude(v);

    v *= mag;
}

float SimStructs::DotProduct(SimVector v1, SimVector v2)
{
    return (v1.x * v2.x + v1.y * v2.y + v1.z * v2.z);
}

SimVector SimStructs::CrossProduct(SimVector v1, SimVector v2)
{
    SimVector ret;
    ret.x = (v1.y * v2.z - v1.z * v2.y);
    ret.y = (v1.z * v2.x - v1.x * v2.z);
    ret.z = (v1.x * v2.y - v1.y * v2.x);
    return ret;
}

Camera code:


void SimCamera::Move(float speed, float timestep)
{
    direction = target - position;
    SimStructs::Normalize(direction);

    position += (direction * speed * timestep);
    target += (direction * speed * timestep);
}

void SimCamera::Strafe(float speed, float timestep)
{
    direction = target - position;
    SimStructs::Normalize(direction);

    strafe = SimStructs::CrossProduct(direction, up);
    SimStructs::Normalize(strafe);

    position += (strafe * speed * timestep);
    target += (strafe * speed * timestep);
}

Usage:


    camera.MouseInput();

    if(globalInput.IsKeyDown(SDLK_w))
        camera.Move(1, frameInterval);
    if(globalInput.IsKeyDown(SDLK_s))
        camera.Move(-1, frameInterval);
    if(globalInput.IsKeyDown(SDLK_a))
        camera.Strafe(-1, frameInterval);
    if(globalInput.IsKeyDown(SDLK_d))
        camera.Strafe(1, frameInterval);

LtJax

168

April 02, 2006 11:59 AM

there's a return missing in your operator*

NickGravelyn

855

Author

April 02, 2006 12:29 PM

Thanks :). I feel kinda dumb now.

LtJax

168

April 02, 2006 12:43 PM

Haha. Don't! Happend at least a 100 times to me before. Strangly enough, MSVC doesn't complain or even warn about it.

_goat

804

April 03, 2006 06:00 AM

Now that you've got your class working, it's time to clean it up and make it watertight. I'll take a Zahlman approach to this (that's right - it's official).

// "typedef" isn't required in C++. You can leave it out happily.struct SimVector{	float x, y, z;		// A constructor will make your life a trillion easier. That's	// right, a trillion. Note we initialise via the initialisation	// list.	SimVector(float x_, float y_, float z_) : x(x_), y(y_), z(z_)	{	}		// You don't need to write an assignment operator ( operator = ),	// because C++ will generate one for your automatically, with a 	// member-wise copy. That's what you've got, so delete it and watch	// it still work.		// You should pass by reference rather by value. this means that	// instead of making a new SimVector, we get given a reference to	// the original one. It is declared "const" so we can't change it.	//	// You should return a (non-const) reference so people can do things	// like:	//    SimVector v = SimVector(3, 4, 5);	//    if ( (v += 4).x == 7 ) go_crazy();	//	SimVector& operator += (const SimVector& v)	{		x += v.x; y += v.y; z += v.z;		return *this;	}		// ...		// it's good practice to make your addition, subtraction, division and 	// multiplication friend operators, because otherwise this:	//   SimVector r = 3.6f * my_simvector;	// won't work, as you have only define an operator * that -takes- a float,	// not a float that takes a SimVector for multiplication.	inline friend SimVector operator + (const SimVector& lhs, const SimVector& rhs)	{		// thanks, constructor!		return SimVector(lhs.x + rhs.x, lhs.y + rhs.y, lhs.z + rhs.z);	}		// finally, -I- prefer to have my major functions as friend functions. it gives	// them the same scope as your class, and makes for a logical place to put them.	inline friend float Magnitude(const SimVector& v)	{		return sqrt(v.x * v.x + v.y * v.y + v.z * v.z);	}}

Hope that helps.

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Help With Vector Math

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