ID3DXLine to world space (instead of screen)

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Hello,

I am using the LPD3DXLINE class. I have 2D sprites being rendered and each sprite has a physics object (4 verlets), I am trying to use the LPD3DXLINE class to Draw lines between each physics verlet/vertex.

But when I pass the physics variables (world space) to the Line-> draw(); function it draws the lines in places I don't want (pixel/screen space, I think)

Here is what I mean:

There should be a red line around each sprite, (the bottom left corner is my world's (0,0)  so when it draws (0,0) it does it from the top left (the screens (0,0)).

So I assume this is a matrix problem? So do I need to give the LPD3DXLINE my view*world*porj matrix?

The LPD3DXLINE->DrawTransform(); function takes D3DVECTOR3 but the ->Draw(); uses a D3DVECTOR2 so I'm confused what to put here?

Or is it somehing else I'm doing wrong?

Here is the code for drawing the lines (if it helps):

	LPD3DXLINE myLine = NULL;
D3DXCreateLine(g_pd3dDevice, &myLine);
myLine->SetWidth(1);
//myLine->SetGLLines(TRUE);

myLine->Begin();

for (int i = 0; i < PhysicsWorld.GetBodyCount(); i++)
{
int size = PhysicsWorld.Bodies[i]->VertexCount;

//int* array=new int[len];
D3DXVECTOR2* Vetecies = new D3DXVECTOR2[size];

for (int j = 0; j < PhysicsWorld.Bodies[i]->VertexCount; j++)
{
Vetecies[j].x =  PhysicsWorld.Bodies[i]->Vertices[j]->Position.x;
Vetecies[j].y =  PhysicsWorld.Bodies[i]->Vertices[j]->Position.y;
}
//myLine->DrawTransform(Vetecies, PhysicsWorld.Bodies[i]->VertexCount, ,
myLine->Draw( Vetecies, PhysicsWorld.Bodies[i]->VertexCount, D3DCOLOR_ARGB( 255, 255, 0, 0 ));
delete Vetecies;
Vetecies = NULL;
}
myLine->End();
myLine->Release();


Thanks

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If your objects are in world space, you need to convert their coordinates to screen space if you want to use the line->Draw() method. The DrawTransform method takes a matrix to automatically transform the vertices for you, and you can read about it on MSDN [url=http://msdn.microsoft.com/en-us/library/windows/desktop/bb174019(v=vs.85).aspx]here[/url]. I suggest you try both methods and see what works for you.

On an unrelated note, why are you calling 'new' inside your loop? Why not just make the list on the stack?

const int size = PhysicsWorld.Bodies[i]->VertexCount;

D3DXVECTOR2 Vetecies[size];

myLine->Draw( &Vetecies, PhysicsWorld.Bodies[i]->VertexCount, D3DCOLOR_ARGB( 255, 255, 0, 0 ));


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If your objects are in world space, you need to convert their coordinates to screen space if you want to use the line->Draw() method. The DrawTransform method takes a matrix to automatically transform the vertices for you, and you can read about it on MSDN here. I suggest you try both methods and see what works for you.

The LPD3DXLINE->DrawTransform(); function takes D3DVECTOR3 but the ->Draw(); uses a D3DVECTOR2 so I'm confused what to put here?

On an unrelated note, why are you calling 'new' inside your loop? Why not just make the list on the stack?

const int size = PhysicsWorld.Bodies[i]->VertexCount;

D3DXVECTOR2 Vetecies[size];

myLine->Draw( &Vetecies, PhysicsWorld.Bodies[i]->VertexCount, D3DCOLOR_ARGB( 255, 255, 0, 0 ));


Because I get the "hast to be a constant value" error if I don't

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The LPD3DXLINE->DrawTransform(); function takes D3DVECTOR3 but the ->Draw(); uses a D3DVECTOR2 so I'm confused what to put here?

Because DrawTransform transforms 3D coordinates to 2D screen coordinates, while Draw directly uses 2D screen coordinates.
As you're doing 2D graphics with sprites, i'd suggest just transforming the vertices manually from your world coords to screen coords.

Because I get the "has to be a constant value" error if I don't

Well then pass in a const int - you did note the const modifier in front of the int in my edited code, right?

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Well then pass in a const int - you did note the const modifier in front of the int in my edited code, right?

Yeah, I know. It still gives me the error though

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Ah ok, my bad, i honestly thought that would work, and had no way to check until now. :)

Theoretically you could use an std::vector<D3DXVECTOR2> and just push back values as needed, and then draw them by passing the address of the first element (&vec[0]), and it would work the same, and would be exception safe too, as right now if you get an exception in between the new and delete calls by any chance, you leak the memory.

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Never mind

Edited by AussieSpoon

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