We add PHP bindings for libgd's features to read and write BMP files, which
are available as of libgd 2.1.0.
As PHP's bundled libgd doesn't yet include the respective features of the
external libgd, we add these.
We expose the image resolution related GD functionality to userland
by introducing `imageresolution()` as getter/setter. Given only the
image argument, it returns the current resolution as indexed array.
Given only a second argument, it sets the horizontal and vertical
resolution to this value. Given three arguments, it sets the horizontal
and vertical resolution to the given arguments, respectively.
There's no need anymore to call an own error handler directly. Instead we
register our error handler and call libgd's error functions (which will
forward). We do this regardless of compiling with the bundled or an external
libgd.
gdImageOpenPolygon() has been introduced with líbgd 2.0.29, so we finally
add a PHP binding for it, and port the respective libgd functionality to
PHP's bundled libgd.
gdLayerMultiply() has been introduced in libgd 2.1.1, and as such would have
been already available for imagelayereffect() with a system libgd. We port
the respective code to the bundled libgd, and also make IMG_EFFECT_MULTIPLY
available to userland.
Instead of rolling our own in the bundled libgd, we use libgd's anti-aliased
drawing API. This way imageantialias() is also available, when built against
a system libgd.
We apply the law `(b**r)**s == b**(r*s)` which holds for all non-negative b
and positive r,s, so a single pow() suffices. Furthermore, we precompute the
gamma, so the refactored code is simpler and faster.
The GD image format is able to handle truecolor images as of libgd 2.0.12
(<https://github.com/libgd/libgd/blob/gd-2.2.3/src/gd_gd.c#L31-L33>).
Therefore we don't need the potentially lossy and time consuming palette
conversion.
This way, imagegd() can also be used to export raw truecolor image data.
As of PHP 5.4.0 the second parameter of all image writer functions (except
imagexbm) accepts also a stream resource. Therefore the parameter name
`filename` is inappropriate. We change it to `to` according to what it's
already called in _php_image_output_ctx().
We consider the reflection only related BC break acceptable for a minor version.
These functions may be used in tight loops to do image manipulation in
userland. Using FAST_ZPP is supposed to bring considerable performance
improvements in this case; we've been able to measure up to 25%.
