Question

I’ve had this problem on a couple of machines now – almost always laptops and I think usually those with Intel graphics chipsets, when using ID3DXLine.

I have some code that vaguely looks like this:

MyLine->SetWidth(MyLineThickness);
MyLine->SetPattern(MyLinePattern);
MyLine->Begin();
{   
    ... Draw some lines with ->MyLine->Draw
}               
MyLine->End();

With MyLine being a CComPtr (ID3DXLine). When MyLineThickness is 1.0, these machines draw thick lines (looking as if they’re drawn with a felt-tip pen!). When I change MyLineThickness to 1.1, or 1.5, I then get nice thin lines. Obviously increasing that to around 8.f will give me thick lines again.

So ID3DXLine on these machines seems to do something really odd when thickness is 1.0. At < 1.f and > 1.f it seems to behave as you would expect!

Has anyone else experienced any strangeness in ID3DXLine? I’m using D3D 9.0c btw, alongside the Feb 2010 SDK.

Answer 1

According to DX9 documentation lines of thickness 1.0f are drawn using native hardware line drawing support if one exists. All other sizes are drawn by producing a pair of triangles and, hence, rendered via vertex shader. Try checking D3DCAPS9::LineCaps for supported capabilities.

After some playing with ID3DXLine I decided to use DrawPrimitives for drawing lines – it’s probably a bit slower but at least you get same result on any system.