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# Mouse in 3D

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Dose anyone have some sample code of how to determin if the mouse is pointing at a 3D object. By 3D object, I meen a list of D3DVERTEX''s. I know the function "PointInPoly" but that only checks a single poly in 2D. Is there anyway to pull the transformed data of the card ? Or transform the Mouse into 3D. If anyone has some sample code it would be great !

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You have to use a technique that''s called "ray casting". First, you get the 3D line that the mouse cursor''s on (it''s like "x=az+b, y=cz+d"). Then, you do some intersection tests with the polygons in the object to see if the rays intersect (if the object''s solid, you only need to test with the polygons whose normals are facing the camera, and you can reuse lighting information with that). Also, if you can access the Z-Buffer on the display card and read from it, you can check the z-buffer''s value at those mouse coordinates and only check with polygons that have points with both higher and lower Z values than that.

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Actually, you should only have to do it in 2d. Just loop through all the polygons it could possibly be on, and see which is the closest that the mouse point is inside of. It works great!

~BenDilts(LPWEBSITE www.geocities.com/benbeandogdilts);

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Dose any of you have some sample code on that ?

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This is how I did it:

D3DVECTOR CMyD3DApplication::MouseTo3D (int x, int y, float z){	double d;	D3DVECTOR tv, norm;	D3DVIEWPORT7 vp;	D3DMATRIX M, preM, invM, Proj, View, World, invProj, invView, invWorld;	m_pd3dDevice->GetViewport(&vp);    	norm.x=(float)((x-vp.dwX)*2.0/vp.dwWidth)-1.0f;	norm.y=(float)((y-vp.dwY)*2.0/vp.dwHeight)-1.0f;	norm.z=0.0f;	norm.y*=-1;	if (z==0)	{		tv.x=viewx;		tv.z=viewz;		tv.y=viewy;	}	if (z==1)	{	m_pd3dDevice->GetTransform(D3DTRANSFORMSTATE_VIEW,(D3DMATRIX *)&View);	m_pd3dDevice->GetTransform(D3DTRANSFORMSTATE_PROJECTION,(D3DMATRIX *)&Proj);	m_pd3dDevice->GetTransform(D3DTRANSFORMSTATE_WORLD,(D3DMATRIX *)&World);	View._14=0;	View._24=0;	View._34=0;	View._44=1;	Proj._14=0;	Proj._24=0;	Proj._34=0;	Proj._44=1;	World._14=0;	World._24=0;	World._34=0;	World._44=1;	D3DMath_MatrixInvert(invView,View);	D3DMath_MatrixInvert(invProj,Proj);	D3DMath_MatrixInvert(invWorld,World);	D3DMath_MatrixMultiply(preM,invProj,invView);	D3DMath_MatrixMultiply(M,preM,invWorld);	D3DMath_VectorMatrixMultiply(tv,norm,M);	}	return (tv);}

The function returns a Vector with the coordinates in the 3D space.
The parameters x/y are the screen mouse-coordinates, z is 1 (point at the near clipping plane) or 0 (the camera point).
After you''ve got the point on the near clipping plane you can make a ray-triangle intersection test for example.

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