Previously it would be multiplied onto the image pixel, but the Render
specification is pretty clear that the alpha map should be used
*instead* of any alpha channel within the image.
This makes the assumption that the pixels in the image are already
premultiplied with the alpha channel from the alpha map. If we don't
make this assumption and the image has an alpha channel of its own, we
would have to first unpremultiply that pixel, and then premultiply the
alpha value onto the color channels, and then replace the alpha
channel.
This program demonstrates three bugs relating to alpha maps:
- When fetching from an alpha map into 32 bit intermediates, we use
the fetcher from the image, and not the one from the alpha map.
- For 64 bit intermediates we call fetch_pixel_generic_lossy_32()
which then calls fetch_pixel_raw_64, which is NULL because alpha
images are never validated.
- The alpha map should be used *in place* of any existing alpha
channel, but we are actually multiplying it onto the image.
There is a couple of bugs in bugzilla where bugs in the X server
triggered asserts in the pixman region code. It is probably better to
let the X server survive this. (In fact, I thought I had disabled them
for 0.16.0, but apparently not).
The patch below uses these rules:
- In _stable_ pixman releases, assertions and selfchecks are turned
off. Assertions, so that the X server doesn't die. Selfchecks,
for performance reasons.
- In _unstable_ pixman releases, both assertions and selfcheck are
turned on. These releases are what get added to development
distributions such as rawhide, so we want as much self-checking
as possible.
- In _random git checkouts_, assertions are enabled, so that bugs
are caught, but selfchecks are disabled so that you can use them
for performance work without having to fiddle with turning
selfchecks off.
Existing template already supports 2D images processing,
but pixman also needs some NEON optimized functions for
improving performance when compositing is decoupled
into "fetch -> process -> store" stages and done via
temporary scanline buffer. That's why a new simplified
template which deals only with the generation of single
scanline processing functions is handy.
There is a couple of bugs in bugzilla where bugs in the X server
triggered asserts in the pixman region code. It is probably better to
let the X server survive this. (In fact, I thought I had disabled them
for 0.16.0, but apparently not).
The patch below uses these rules:
- In _stable_ pixman releases, assertions and selfchecks are turned
off. Assertions, so that the X server doesn't die. Selfchecks,
for performance reasons.
- In _unstable_ pixman releases, both assertions and selfcheck are
turned on. These releases are what get added to development
distributions such as rawhide, so we want as much self-checking
as possible.
- In _random git checkouts_, assertions are enabled, so that bugs
are caught, but selfchecks are disabled so that you can use them
for performance work without having to fiddle with turning
selfchecks off.
This fix prevents build failure due to not accepting PLD instruction when
compiling for armv4 cpu with the relevant -mcpu/-march options set in CFLAGS.
