Projectile Movement C++

For Beginners

Started by mypel16000 January 09, 2013 10:36 PM

9 comments, last by mypel16000 11 years, 3 months ago

Author

January 09, 2013 10:36 PM

Hi, I am using C++ and trying to make my player shoot projectiles. I have done OK so far, but the problem is that what I have done to move them is just use:

bulletX += xOffset( betwen player and mouse ) /100

bulletY += yOffset / 100

This gave me the right direction although there was an issue, the closer the mouse was to the player, the slower the bullet went ( as you can probably tell from the code above ). I have tried:

Dlen = sqrt(Dx*Dx + Dy*Dy)

Dx/=Dlen;

Dy/=Dlen

Bx=Bx+Dx*Bs;

By=By+Dy*Bs;

*Dlen = normalised value, Dx = xOffset, Dy = yOffset, Bx= bulletX, By= bulletY, Bs = bullet Speed.

but I was unsuccesful.... the bullet went in completely random directions very different to where I was aiming.

I also tried to find a ratio :

yOffset / xOffset and then always move X by 1 or -1 and y by 1 or -1 multiplied by the ratio.

Again unscuccesful.

Is there any way to achieve a constant speed when shooting projectiles from a player in the direction of the mouse cursor that will work? Please put an explained example.

Madhed

4,095

January 10, 2013 12:13 AM

Using the normalised difference vector is correct.

What data type are you using to store Dx, Dy? If you are using int, that won't work because the decimal component will be truncated.

Use float instead.

incertia

787

January 10, 2013 01:37 AM

Probably because integers are bad for division.

what

Aardvajk

13,217

January 10, 2013 03:25 PM

Here's a very basic 2D vector class:

[source]
#ifndef VEC2_H
#define VEC2_H

#include

class Vec2
{
public:
Vec2(){ }
Vec2(float x, float y) : x(x), y(y) { }

Vec2 &operator+=(const Vec2 &v){ x += v.x; y += v.y; return *this; }
Vec2 &operator-=(const Vec2 &v){ x -= v.x; y -= v.y; return *this; }

Vec2 &operator*=(float v){ x *= v; y *= v; return *this; }

Vec2 operator+(const Vec2 &v) const { Vec2 r = *this; r += v; return r; }
Vec2 operator-(const Vec2 &v) const { Vec2 r = *this; r -= v; return r; }

Vec2 operator-() const { return *this * -1.0f; }

Vec2 operator*(float v) const { Vec2 r = *this; r *= v; return r; }

float dot(const Vec2 &v) const { return (x * v.x) + (y * v.y); }

float length() const { return sqrt(dot(*this)); }

Vec2 normalised() const { float n = length(); return Vec2(x / n, y / n); }

float x, y;
};

inline Vec2 operator*(float f, const Vec2 &v){ Vec2 r = v; r *= f; return r; }

#endif // VEC2_H
[/source]

Now it is simple:

[source]
void f()
{
Vec2 pos(50, 40);
Vec2 target(200, 300);

Vec3 dir = target - pos;
dir = dir.normalised();

while((target - pos).length() < epsilon)
{
pos += dir * speed;
}

pos = target;
}
[/source]

A vector class with overloads is a great idea when doing this kind of stuff.

Post editor ate my spaces. Sorry. The editor is still glitchy as hell on this site.

journal | website | twitter | youtube

Serapth

6,672

January 10, 2013 05:47 PM

Check out this tutorial on the math behind sprite based shooting. It's Javascript based, but the code is easily groked to a C++ programmer. The entire math tutorial series may prove helpful.

Huge Collection of Game Development Tutorials || Getting Started? Start Here

mypel16000

Author

January 11, 2013 08:03 PM

Soz

Madhed

4,095

January 11, 2013 09:58 PM

[quote name='mypel16000' timestamp='1357934604' post='5020436']
@Madhed: You are not really helping...
[/quote]

Why is that so? Tell me why it wasn't helpful and I might give it another try.

BeerNutts

4,410

January 11, 2013 10:14 PM

@Madhed: You are not really helping...
@Serapth: That tutorial has exactly the same problem as me....

Any more GOOD help??

Good luck getting any more help with those kind of response.

My Gamedev Journal: 2D Game Making, the Easy Way

---(Old Blog, still has good info): 2dGameMaking
-----
"No one ever posts on that message board; it's too crowded." - Yoga Berra (sorta)

Serapth

6,672

January 12, 2013 03:47 AM

@Madhed: You are not really helping...
@Serapth: That tutorial has exactly the same problem as me....

Any more GOOD help??

Yeah.... On. Your. Own.

Enjoy never, ever getting help from me.

Ciao.

Huge Collection of Game Development Tutorials || Getting Started? Start Here

Aardvajk

13,217

January 12, 2013 02:14 PM

Madhead's advice was extremely relevant and correct. The tutorial that Serapth linked to blatantly doesn't suffer from the same issues as you - have you actually tried clicking on the window top right on that page and observing the projectiles moving towards the mouse point rather than going in "completely random directions"?

Two minutes on Google would have answered your question. Instead you choose to take up our time by posting on a forum, then act very rudely to respondents.

Think on please.

journal | website | twitter | youtube

Projectile Movement C++

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