• Ronald S. Bultje's avatar
    swscale: fix overflows in vertical scaling at top/bottom edges. · d49352c7
    Ronald S. Bultje authored
    This fixes integer multiplication overflows in RGB48 output
    (vertical) scaling as detected by IOC. What happens is that for
    certain types of filters (lanczos, spline, bicubic), the
    intermediate sum of coefficients in the middle of a filter can
    be larger than the fixed-point equivalent of 1.0, even if the
    final sum is 1.0. This is fine and we support that.
    
    However, at frame edges, initFilter() will merge the coefficients
    for the off-screen pixels into the top or bottom pixel, such as
    to emulate edge extension. This means that suddenly, a single
    coefficient can be larger than the fixed-point equivalent of
    1.0, which the vertical scaling routines do not support.
    
    Therefore, remove the merging of coefficients for edges for
    the vertical scaling filter, and instead add edge detection
    to the scaler itself so that it copies the pointers (not data)
    for the edges (i.e. it uses line[0] for line[-1] as well), so
    that a single coefficient is never larger than the fixed-point
    equivalent of 1.0.
    d49352c7
swscale.c 108 KB