gpu: add binding flags to Backend.NewTexture

Direct3D needs to know the texture bind usage up front, in particular
whether the texture is going to be used as a render target.

Signed-off-by: Elias Naur <mail@eliasnaur.com>

gpu/path.go

@@ -210,7 +210,8 @@ func (s *fboSet) resize(ctx Backend, sizes []image.Point) {
 				f.tex.Release()
 			}
 			f.size = sz
-			f.tex = ctx.NewTexture(TextureFormatFloat, sz.X, sz.Y, FilterNearest, FilterNearest)
+			f.tex = ctx.NewTexture(TextureFormatFloat, sz.X, sz.Y, FilterNearest, FilterNearest,
+				BufferBindingTexture|BufferBindingFramebuffer)
 			f.fbo.BindTexture(f.tex)
 		}
 	}