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# Firing from cross hair towards the forward direction

## 10 posts in this topic

I'm trying to allow the player to fire from their weapons, what I'm doing is that I will cast a ray from the middle of the screen to a forward direction, so I will have a method like void fire(float distance) doing the following;
D3DXVECTOR3 rayFrom = ScreenToWorld(); // rayFrom = Cross hair position, middle of the screen position in 3D
D3DXVECTOR3 rayTo = ???;

How do I set rayTo? it should be FORWARD since the cross hair always shoot forward, I want to set the value of rayTo while taking care of the parameter float distance so I can allow the player to fire and limit the distance.
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This depends directly on your other query, regarding zoom effect.

Ideally, you can set your limit to the distance upto which your view doesn't get inverted.

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@NewDisplayName: This question is not related to the other question regarding the zoom effect, I'm trying to get rayTo by using the two values rayFrom and distance. Edited by Medo3337
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Well, if you're trying to figure out the maximum distance your weapon can fire efficiently then it is the value at which your FOV changes to an upside down world.

That's how I meant that this is related to your other query.

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No it isn't. His mistake last time was adding an amount on to the FOV (potentially going above 180 degrees/PI radians) when he should have been dividing the FOV by a factor (multiplying by a value between 0 and 1).

Are you casting a ray backwards from the desired hit point? Because that sounds backwards to me, you need to fire a ray from the weapon muzzle along the direction from the muzzle to the desired hit point, and if you want to limit the range you need to normalise the fire direction and scale it by the max range for the weapon.
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@Paradigm Shifter: No, it's not backward, I'm trying to cast a ray from the cross hair to the forward direction (limited to certain range)

Take a look at what I'm doing:

D3DXVECTOR3 ScreenToWorld(HWND Hw,float X,float Y,const D3DXMATRIX &View,const D3DXMATRIX &Proj)
{
RECT R; GetClientRect(Hw,&R);
D3DVIEWPORT9 Vp;
Vp.X=R.left;
Vp.Y=R.top;
Vp.Width=R.right-R.left;
Vp.Height=R.bottom-R.top;
Vp.MinZ=0;
Vp.MaxZ=1;
D3DXVECTOR3 V(X,Y,0);
D3DXMATRIX World; D3DXMatrixIdentity(&World);
D3DXVec3Unproject(&V,&V,&Vp,&Proj,&View,&World);
return V;
}

// WEAPON FIRING RAYCASTING

rayFrom = ScreenToWorld(hWnd, WINDOW_WIDTH/2, WINDOW_HEIGHT/2, &viewMatrix, &projectionMatrix); // From cross hair

rayTo = ?; // The direction should be forward from the origin (the cross hair)

Raycasting(rayFrom, rayTo);

// Code to test for hit here and then apply damage...

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The cross hair isn't the origin... it's the target. The gun muzzle (or the camera) is the origin...
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If you unproject both (X, Y, 0.0f) and (X, Y, 1.0f) you can use the difference between those two positions to find the direction you need.

If you normalize that direction vector and then scale it by the distance parameter you'll have your destination point. Just make sure you do the subtraction in the correct order or you'll be shooting backwards.

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The cross hair isn't the origin... it's the target. The gun muzzle (or the camera) is the origin...

So, that means I was not working on the correct way, I changed the code to:

D3DXVECTOR3 rayFrom = camera->GetPosition();
D3DXVECTOR3 rayTo = ScreenToWorld(...);
Raycasting(rayFrom, rayTo);


Is that the correct way?

Let me know how I can set the distance (range the bullet can hit).

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Try it and see (draw some debug arrows or points along the ray, see if they look correct).

To set the range, normalise the direction vector (rayTo - rayFrom) and scale it by the distance you can fire.
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Okay, I tried the following but can't get it to work yet:

float distance = 1000.0f;
D3DXVECTOR3 rayFrom = camera->GetPosition();
D3DXVECTOR3 rayTo = ScreenToWorld(hWnd, WINDOW_WIDTH/2, WINDOW_HEIGHT/2, camera->viewMatrix(), camera->projectionMatrix());
D3DXVECTOR3 direction;
D3DXVec3Normalize(&direction, &(rayTo - rayFrom));
D3DXVec3Scale(&direction, &direction, distance);
Raycasting(rayFrom, direction);
Edited by Medo3337
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