pointsizes

It depends on whether point smoothing is enabled. With smoothing disabled (the default state), it should look like case 1. The width is 2, so the point should be 2x2 pixels.

However, if point smoothing is enabled, which fragments are generated depends not on whether they are within a square centered at the points coordinate, but whether they are within a circle of diameter equal to the point size. In that case, I don't really know for sure, but a combination of case 1 and 2 I would guess (pixels can be "partially" rendered, where the alpha channel represents pixel coverage).

For questions like this, consult the API specification. Page 95, section 3.3, in the OpenGL 2.0 specification described how points should behave.

ok i jus have a look at those few pages of the glspec.

jus one other qn:
lets say i got 2 points that have pointsize 3, such that these overall area covered by the 2 points are overlapped for some parts. Would it be the case that fragments that cover the overlapped region, are rasterized twice?

thx!