What you're experiencing here is normal behavior.
When you draw a quad or any other polygon, if you switch on filtering all it does is filter the internal pixels of the polygon. It still considers the edges of the polygon to be whole pixels. It doesn't alphablend the edges with the background. When you position your object at a sub-pixel floating point coordinate, it will try to properly weight the pixel colors to make it look like the object is positioned accurately, but it still wont do anything to make the edge look smooth, especially at a rotation angle.
What you're doing when you add a `border` around the edge of the actual graphic that you want to draw, you're giving it extra allowed space in which to continue filtering. So then there is pixel space in which to apply the filtering process because it's technically within the polygon boundaries.
What you normally would need to do, to allow your graphic to go to the edges and still have a smooth edge, is to switch on polygon smoothing which is a separate process that actually alphablends/antialiases the edge of the polygon with what is behind it. I also have heard you need to enable blending and set it to a modulation mode in order for the polygons to be properly antialiased together. At least this is how I think it works in OpenGL. I'm not surprised you see jitters and stuff at the edge of your objects if you don't have polygon smoothing switched on. I noticed this on my blobby objects demo thing, where the internals are perfectly filtered but the edges were as if integer-based.
Having said all that, it is a good tip to know that adding a border around the image helps with filtering the edges.
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