Hardware / software support for scaling?

SDL Development
1

I’m trying to figure out why plaympeg (smpeg), when told to double the
size of an image, looks good on some machines and very pixelated on
other machines. In tracing through the code, it appears that a frame
is simply blit’ed with the source rectangle being the size of the mpeg
frame, and the destination rectangle being the requested scale size
(twice the mpeg size).

  • Does SDL do any interpolation of pixels during scaling?
    If not, where in the source would I look to possibly add such
    interpolation?

  • Do some graphics cards do interpolation of pixels during a scaling,
    while others do not? If so, what “named feature” would I look for
    to search for the lowest-end video card that supports that
    interpolation?

Thanks!

Derrell

2

I’m trying to figure out why plaympeg (smpeg), when told to double the
size of an image, looks good on some machines and very pixelated on
other machines. In tracing through the code, it appears that a frame
is simply blit’ed with the source rectangle being the size of the mpeg
frame, and the destination rectangle being the requested scale size
(twice the mpeg size).

  • Does SDL do any interpolation of pixels during scaling?
    If not, where in the source would I look to possibly add such
    interpolation?

No. Look in src/video/SDL_stretch.c

  • Do some graphics cards do interpolation of pixels during a scaling,
    while others do not? If so, what “named feature” would I look for
    to search for the lowest-end video card that supports that
    interpolation?

Yes, but I’m not sure which cards do it wit XVideo and which don’t.
Are you running under Linux or Windows?

See ya,
-Sam Lantinga, Lead Programmer, Loki Software, Inc.

3

Sam Lantinga writes:

  • Do some graphics cards do interpolation of pixels during a scaling,
    while others do not? If so, what “named feature” would I look for
    to search for the lowest-end video card that supports that
    interpolation?

Yes, but I’m not sure which cards do it wit XVideo and which don’t.
Are you running under Linux or Windows?

Sorry, should have specified. I’m running under Linux.

Derrell