WebGradients: redo implementation

The previous implementation was *extremely* expensive. It
relied on loading a binary JSON file from resources (which
involved decompressing it), then extracting information out of
it to build a gradient.  Already-loaded gradients were kept in
a local cache, which had to be mutex protected.

Instead, this patch extends the gradient generator to build
static arrays filled with the web gradient data, sitting in
.rodata.

These arrays are used when building QGradient objects with a
web gradient. No explicit mutex protection is necessary, since
accesses will just read from the arrays.

As benefits, this patch removes:

* the binary json representation from QtGui's resources (~4KB
compressed, ~50KB uncompressed)
* the overhead of reading from the JSON for each used web
gradient;
* the startup costs of registering the webgradients in the
resources;
* all the overhead of mutex locking when building such
gradients;
* all the runtime memory allocations to load, parse and cache
the web gradients (including the memory + CPU spike on first
load due to the uncompression of the JSON data, as well as a
couple of deep copies).

Change-Id: If5c3d704430df76ce8faf55ee75ebd4639ba09c4
Reviewed-by: Tor Arne Vestbø <tor.arne.vestbo@qt.io>
Reviewed-by: Ulf Hermann <ulf.hermann@qt.io>
Reviewed-by: Qt CI Bot <qt_ci_bot@qt-project.org>
Reviewed-by: Thiago Macieira <thiago.macieira@intel.com>
Reviewed-by: Edward Welbourne <edward.welbourne@qt.io>

1 files changed, 21 insertions, 0 deletions

diff --git a/util/gradientgen/WEBGRADIENTS_LICENSE.txt b/util/gradientgen/WEBGRADIENTS_LICENSE.txt
new file mode 100644
index 0000000000..1a4d527a4d
--- /dev/null
+++ b/util/gradientgen/WEBGRADIENTS_LICENSE.txt
@@ -0,0 +1,21 @@
+MIT License
+
+Copyright (c) 2017 itmeo
+
+Permission is hereby granted, free of charge, to any person obtaining a copy
+of this software and associated documentation files (the "Software"), to deal
+in the Software without restriction, including without limitation the rights
+to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
+copies of the Software, and to permit persons to whom the Software is
+furnished to do so, subject to the following conditions:
+
+The above copyright notice and this permission notice shall be included in all
+copies or substantial portions of the Software.
+
+THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
+IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
+FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
+AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
+LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
+OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE
+SOFTWARE.