This makes for a chroma plane of 2x2. The SIMD versionf of generic
downscalers assume that the width and height is at least 2, since
it does an unconditional loop for the body of the image, and a
separate step for the last pixel and last row. The SIMD versions
assume that (width-1) and (height-1) are larger than zero.
This fixes spurious crashes in EncodeDecodeTestAPI.SetOptionEncParamExt.
When calculating what resolution to actually downscale to,
it can end up smaller than what the caller set. When scaling
down to resolutions close to the limit of allowed values,
this can end up setting values lower than the limit.
Previously, e.g. a downscale from 2266x8 to 566x2 will end
up as 566x1 after this calculation. When scaling to a
566x1, the chroma plane gets a height of 0, which doesn't
make sense, and which breaks e.g. the SSE2 scaler. Therefore,
make sure none of the dimensions end up set below 2.
Normally, the DownsamplePadding skips scaling if the target
size is the same as the source size, assuming that the caller
will use the source data pointer in that case. This is true
for the base layer (the first call to DownsamplePadding in
SingleLayerPreprocess), but when downsampling the other layers,
there is no special handling for the case when the target
is the same size as the source.
Previously, the encoding of such spatial layers will use
completely uninitialized data, encoding complete garbage.
Instead force DownsamplePadding to make a copy if no scaling
is required, for the dependency layers. The base layer still
avoids a copy unless scaling of that layer is required.
Whether it actually makes sense to have lower spatial layers
the same size as the original one is a different question
though - currently the code allows it, and
EncodeDecodeTestAPI.SetOptionEncParamExt will try to use it.
They are still used slightly differently in the encoder and decoder;
the decoder uses plain functions while the encoder uses one object
keeping track of the number of allocated bytes, and keeping track
of the requested alignment.
When generating a new version of the header, that includes the
actual git hash, don't overwrite the file that is tracked by git.
Instead create a new file, and include this only if the build system
indicates that it exists (by setting a define). This allows the
untouched source tree to be built from within an IDE even if make
has not been run.
This reduces the hassle with a file that needs to be ignored in the
git configuration.
The downside is that the generated file isn't used if building
from within an IDE, if the header has been updated by calling make
before (since the IDE configuration doesn't know whether the user
actually has run make). Since users of the IDE might not build via
make in the command line at all (in the same source checkout at least),
this should not be an issue in practice. The previous way things worked,
the version hash (generated by make) when used in an IDE could actually
be outdated and misleading.
This function actually zero-initializes the allocated memory, thus
make this clear in the function name.
This makes the function name match the same behaviour in the encoder.
Use the decoder versions of the functions (which are capable
of handling widths 4/8/16 for luma, not only 16 as in the
encoder). By using the more generic versions, there may be a small
performance loss since the functions need to check the width
in every call. Actual measurements show that the actual change is
very small (and the shared routines turn out to actually be faster
than the existing ones in ARM NEON setups).
