In case the cached thumbnail loaded successfully the isNull check is
unreachable due to the early `return true`.

The QSaveFile is only needed if there is thumbnail creator for the
format of the current file.

Minimum Qt version set in CMakeLists.txt is 5.11, so the checks are
redundant.

QImage::load(<path>) tries to find a fallback image if the file does
not exist, by appending extensions of all supported file formats, as
QImageReader defaults to format autodetection.

Check if the file exists, and only then try to load it.

Cached thumbnails should not depend on varying properties of the caller,
like iconAlpha, iconSize and theme of the overlay icon.

Also, the current mime type icons are hardly visible and unrecognizable
with dolphins default opacity of ~25%.

BUG: 425789

Despite the name, fileUrl is already a QByteArray encoded URL here.

According to the spec, at least Thumb::URI and Thumb::MTime are required.

KIO::PreviewJob discards any thumbnails without these and recreates
the thumbnails.

If the inner loop is not run, skipped will be 0 and the loop is left
anyway.

As `skipped` is always reset to 0, the condition is always true.

Change the skipValidItems calculation to make it more obvious it
calculates the remainder, and is always a positive value.

Declare skipped inside the loop, as it is only used inside the loop.

No functional changes.

The branches can be simplified to an arithmetic operation.

Replace the `yPos <= maxYPos)` check in the inner loop with an more
explicit check whenever a thumnail is drawn.

`(yPos <= maxYPos) && !validThumbnails)` is redundant, as yPos is only
incremented whenever validThumbnails is incremented. Move the
validThumbnails check into the loop.

Stefan Brüns authored Aug 28, 2020 and David Faure committed Aug 29, 2020

The URI is only required when a thumbnail is created or looked up.

Stefan Brüns authored Aug 21, 2020 and David Faure committed Aug 29, 2020

Commit 8ed64be9 ("Enlarge image in folder preview when there's only
one image") made createSubThumbnail part of drawSubThumbnail. As a side
effect, when skipValidItems is > 0, the thumbnail is not only fetched
but also drawn in the top left position.

Split fetching and drawing again.

This is visible in the file dialogs (dolphin only uses sequenceIndex==0),
when hovering a directory with the mouse.

Stefan Brüns authored Aug 21, 2020 and David Faure committed Aug 29, 2020

Scaling down a large thumbnail is considerably faster than creating the
thumbnail from scratch.

Stefan Brüns authored Aug 21, 2020 and David Faure committed Aug 29, 2020

If a thumbnail already exists, the mimetype of the original file and
available plugins do not matter.

Saves accessing the original file, and allows thumbnails for file types
which are not natively supported by KIO.

The second condition can never be fulfilled on the first iteration
(QDirIterator does not return a path twice), but only after the
QDirIterator has been reset in the outer loop.

As validThumbnails is incremented when hadFirstThumbnail gets assigned,
the outer loop will never be run after the initial assignement of
hadFirstThumbnail, so the condition can never be true.

Instead of doing a lookup for a thumbnail which is guaranteed to to not
exist, and then trying to find a suitable plugin, which exists neither,
just skip the file.

DrawFrame has been deprecated since KF 5.32, see
frameworks/kio@8d9fde5d

`url` is either a `thumbnail:` URL or a local URL (when called from
the m_propagationDirectories recursion), in both cases only the local
path is relevant.

Always supply a local path to the thumbForDirectory method, this also
avoids creation of a temporary QUrl.

Make the path canonical, as the path will be used will be used for
determining the thumbname hash and the Thumb::URI metadata field.
Otherwise, the directory thumbnailer will create duplicate thumbnails
for e.g. symlinked directories:

https://specifications.freedesktop.org/thumbnail-spec/thumbnail-spec-latest.html#THUMBSAVE
> You need the absolute canonical URI for the original file,
> as stated in URI RFC 2396.

Instead of returning an unspecific error later, when ThumbCreator::create
fails due to a nonexisting or unreadable file, immediately error out.

Same as in kio core, see
frameworks/kio@371e523f

BUG: 419566
FIXED-IN: 20.08

GIT_SILENT

The maximum size for local thumbnails was raised from 5 MB to unlimited elsewhere.

BUG: 238690

Differential Revision: https://phabricator.kde.org/D15741

When there is only one thumbnail it is painted larger. This pixmap is always generated, even if we
ended up creating more than one thumbnail.
This patch makes it remember the first valid thumbnail and paints the larger pixmap only as needed.

Differential Revision: https://phabricator.kde.org/D15402

The thumbnailer lives in a separate application, so it will read the enabled plugins from a different configuration than the
calling application (e.g. dolphinrc).
This leads to folder thumbnails following the default settings instead of user-configured settings, causing disabled plugins
to be used and blacklisted thumbnails never being used even if enabled by the user.

BUG: 388303

Differential Revision: https://phabricator.kde.org/D15097

The HTML thumbnailer uses WebEngine, so we need to set this attribute
(before we create a QGuiApplication) in order to get rid of an annoying
warning in the kdeinit (or kioslave) process.

Summary:
If a custom folder icon is smaller than the requested preview size
`KIO::PreviewJob` returns a pixmap of only that size. E.g. `dolphin`
scales this up to its current thumbnail size which results in ugly
overlay icons for very small folder icons. If the folder icon is
scaled up before creating the overlay icons the overall preview
looks much better.

CCBUG: 315983

Test Plan:
# Set a small custom icon (e.g. 32 px) for a folder containing images
# Start dolphin with `Preview` enabled in the parent folder
# Zoom thumbnails to e.g. 128 pixels overlay
# The overlayed preview icons should not be blurry

| Before:    | After:     |
| {F5837958} | {F5837960} |

Reviewers: #frameworks, rkflx

Reviewed By: rkflx

Subscribers: ngraham, rkflx

Differential Revision: https://phabricator.kde.org/D12734

Summary: master now has KF 5.40, so require that and always use KIO::PreviewJob::defaultPlugins(), which lets us get rid of some unnecessary code

Test Plan: Tested in KDE Neon. Compiles and deploys fine.

Reviewers: #frameworks, broulik, elvisangelaccio

Reviewed By: elvisangelaccio

Differential Revision: https://phabricator.kde.org/D8847

Summary:
Use KIO::PreviewJob::defaultPlugins() instead of hardcoding plugin list.

Depends on D8347

Test Plan: Compiles fine in KDE Neon.

Reviewers: #frameworks, broulik, elvisangelaccio, markg

Reviewed By: #frameworks, elvisangelaccio, markg

Differential Revision: https://phabricator.kde.org/D8352

Summary:
Use KIO::PreviewJob::defaultPlugins() instead of hardcoding plugin list.

Depends on D8347

Test Plan: Compiles fine in KDE Neon.

Reviewers: #frameworks, broulik, elvisangelaccio, markg

Reviewed By: markg

Differential Revision: https://phabricator.kde.org/D8352

Test Plan:
Compiles fine under Linux
Compiles fine under Windows

Reviewers: bcooksley, dfaure, marten

Reviewed By: dfaure

Differential Revision: https://phabricator.kde.org/D6151