However it's not working. It selectes only the tile that would be 0,0 in the original system (the non rotated, top view) and it does so for about width/2 to the left and height/2 above. This made me realize though that I failed to mention my coordinate system (XNA) has it's (0,0) at the top left, not the bottom left of the window.
Yesterday I've tried thinking up some formulas, but to no avail. I was sure this would be correct, but it doesn't work for some reason... I'll have to try again after work..
x = mX / TileWidth + (mY / TileHeight / 2 - maxX / 2) * TileWidth y = mY / TileHeight + (mX / TileWidth / 2 - maxY / 2) * TileHeight
mX is the mouse X position, offsetted by the X drawing offset
mX is the mouse Y position, offsetted by the Y drawing offset
maxX is the number of virtual tiles on X axis
maxY is the number of virtual tiles on Y axis
what virtual tiles means is, the bounding rectangle of a drawn tile, divided by 2, by an axis is in the non-rotated top view, not the isometric view.
Ofcourse, it should work only for that virtual tile and then I could use a color map to determine which exact tile is selected, but even without a color map, I can see this does not work.