This is a companion to gdk_texture_save_to_png, using
the tiff format, which will let us avoid lossy conversion
of HDR data, since we can store floating point data.
A private vfunc that downloads a texture as a GdkMemoryTexture in
whatever format the texture deems best.
There are multiple reasons for this:
* GLES cannot download the Cairo format. But it can download some
format and then just delegate to the GdkMemoryTexture implementation.
* All the other download vfuncs (including the ones still coming) can
be implemented via download_texture() and delegation, making the
interface easier.
* We want to implement image loading and saving support. By using
download_texture(), we can save in the actual format of the texture.
* A potential GdkCompressedTexture could be implemented by just
providing this one vfunc as a compress() step.
Remove a boatload of "or %NULL" from nullable parameters
and return values. gi-docgen generates suitable text from
the annotation that we don't need to duplicate.
This adds a few missing nullable annotations too.
The fact that we are using gdk-pixbuf for loading files currrently does not mean we will use it going forward.
Also, "anything gdk-pixbuf can load" does not mean anything, because what gdk-pixbuf can load is a compile-time option.
As new_from_resource() will assert() if it cannot load a resource, we must be very sure that people do not use anything but PNG and JPEG for resources and the docs were not clear on that.
A problem with textures is that they can become too big for GPU memory,
which would require tiling. But for tiling we only need to download
the pixels needed by the tile.
Similarly, there might be interest to not upload full textures if a
renderer knows it only needs a small part.
Both of these methods require the ability to specify an area of the
texture to be downloaded. So change the download vfunc to include
this parameter now before we add even more textures later.
A private gdk_texture_download_area() function has also been added, but
nobody is using it yet.
GdkMemoryTexture is a texture implementation for holding data in memory
(read: GBytes). You specify the GdkMemoryFormat that data is in and off
you go.
Renderers can use this to add uploads in various different formats and
don't need to fallback to GDK doing the conersion on the CPU.
Supported formats can be extended if we need new ones, for now I just
added the relevant ones for Cairo and GdkPixbuf.
The constructor is also private still, because I'm not sure we want to
export GdkMemoryFormat.
Wrappers that do from_cairo_surface() and for_pixbuf() do exist though.
Put GdkGLTexture into its own file and rename the API to
gdk_gl_texture_foo() instead of gdk_texture_foo_for_gl().
Apart from naming, no actual code changes.
Remove all the old 2.x and 3.x version annotations.
GTK+ 4 is a new start, and from the perspective of a
GTK+ 4 developer all these APIs have been around since
the beginning.
