Hello all! I finally managed to get my Tile picking code working well badly anyway. As the picture below illustrates something is seriously wrong here. I was following the guidelines on http://www.toymaker.info/Games/html/picking.html (Which is really good BTW) and here is my MouseOver() function which detects if the mouse is over a tile: And here is a picture of my problems: Please help me out [help] so close but yet so far!

No the vertices for the triangles are transformed into World View when they are created and then stored in vectors which can be accessed later. here is how I do it:

D3DXVec3TransformCoord(&W1, &D3DXVECTOR3(-1.0f, -1.0f, 0.0f), &WorldMat);	D3DXVec3TransformCoord(&W2, &D3DXVECTOR3(-1.0f, 0.5f, 0.0f), &WorldMat);	D3DXVec3TransformCoord(&W3, &D3DXVECTOR3(0.0f, -1.0f, 0.0f), &WorldMat);	D3DXVec3TransformCoord(&W4, &D3DXVECTOR3(0.0f, 0.5f, 0.0f), &WorldMat);

It may be a problem here I'm not sure but after researching object picking it seems there are two ways of casting a ray from the cursor...

Also in regards to your suggestion:

D3DXMatrixInverse(&invView, NULL, &ViewMat);
D3DXMatrixInverse(&invWorld, NULL, &WorldMat);

D3DXMATRIX m = (invView * invWorld);

Then what do we do with the Matrix m, should that be passed to InteresectTri()?

Yeah ill try using the untransformed vertices, I'll report back with my findings.
No, passing the untrasformed vertices to D3DXIntersectTri()doesn't do anything not even bad picking.

Woo I've made some progress I changed:

m3d.x = (((2.0f * mousex) / width) - 1) / ProjMat._11; //Converts 2D mouse coordinates into 3D world coordinates	m3d.y = -(((2.0f * mousey) / height) - 1) / ProjMat._22; //Converts 2D mouse coordinates into 3D world coordinates

to

m3d.x = (((2.0f * mousex) / d3dpp.BackBufferWidth) - 1) / ProjMat._11; //Converts 2D mouse coordinates into 3D world coordinates	m3d.y = -(((2.0f * mousey) / d3dpp.BackBufferHeight) - 1) / ProjMat._22; //Converts 2D mouse coordinates into 3D world coordinates

And now I can select the tiles in the first column perfectly however the rest are still totally off! Oh I should also say the intersect is perfect now as far as no tile is selected if the cursor is over the black. If that made any sense.

I think it might be a problem with the way I am creating and checking for intersect on my tiles. i am using two for loops to create the tile grid and this may be messing up the Tile ID numbers... I'll experiment.

Hehe yeah it was that it was creating the tiles in a totally weird order so tile number 2 might've been next to tile number 37! But yeah it all works now but the framerate has dropped DRAMATICALLY! I am checking for mouse over every frame, could that be why? And also I am rendering and checking all the tiles even if they are not on screen, how do you check if an object isn't on screen?