I've written a simple outline shader that adds a single pixel border around a sprite. It works well, except because sprite textures are commonly cropped, the outline is missing at the edges of the image. I've included a blown up image to show you what I mean. See how the border is missing at the tops of the ears and at the extremities of the limbs?
What's the common way of dealing with shaders (like outline, blur, glow, etc.) that go over the edge of a cropped texture? Is there an easy way of adding a transparent margin around a texture? Or do I need to write a vertex shader to expand the size? I'm a little new to this, so I'd be grateful to learn of any solutions people might have.