QGIS API Documentation 3.39.0-Master (3783037d301)
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A cache for images derived from raster files. More...
#include <qgsimagecache.h>
Signals | |
void | remoteImageFetched (const QString &url) |
Emitted when the cache has finished retrieving an image file from a remote url. | |
Signals inherited from QgsAbstractContentCacheBase | |
void | remoteContentFetched (const QString &url) |
Emitted when the cache has finished retrieving content from a remote url. | |
Public Member Functions | |
QgsImageCache (QObject *parent=nullptr) | |
Constructor for QgsImageCache, with the specified parent object. | |
~QgsImageCache () override | |
long | maximumSize () const |
Returns the maximum size of the cache, in bytes. | |
int | nextFrameDelay (const QString &path, int currentFrame=0, bool blocking=false) |
For image formats that support animation, this function returns the number of milliseconds to wait until displaying the next frame in the animation. | |
QSize | originalSize (const QString &path, bool blocking=false) const |
Returns the original size (in pixels) of the image at the specified path. | |
QImage | pathAsImage (const QString &path, const QSize size, const bool keepAspectRatio, const double opacity, bool &fitsInCache, bool blocking=false, double targetDpi=96, int frameNumber=-1, bool *isMissing=nullptr) |
Returns the specified path rendered as an image. | |
void | prepareAnimation (const QString &path) |
Prepares for optimized retrieval of frames for the animation at the given path. | |
int | totalFrameCount (const QString &path, bool blocking=false) |
Returns the total frame count of the image at the specified path. | |
Public Member Functions inherited from QgsAbstractContentCache< QgsImageCacheEntry > | |
QgsAbstractContentCache (QObject *parent=nullptr, const QString &typeString=QString(), long maxCacheSize=20000000, int fileModifiedCheckTimeout=30000) | |
Constructor for QgsAbstractContentCache, with the specified parent object. | |
~QgsAbstractContentCache () override | |
Public Member Functions inherited from QgsAbstractContentCacheBase | |
QgsAbstractContentCacheBase (QObject *parent) | |
Constructor for QgsAbstractContentCacheBase, with the specified parent object. | |
Friends | |
class | TestQgsImageCache |
Additional Inherited Members | |
Static Public Member Functions inherited from QgsAbstractContentCacheBase | |
static bool | isBase64Data (const QString &path) |
Returns true if path represents base64 encoded data. | |
static bool | parseBase64DataUrl (const QString &path, QString *mimeType=nullptr, QString *data=nullptr) |
Parses a path to determine if it represents a base 64 encoded HTML data URL, and if so, extracts the components of the URL. | |
Protected Slots inherited from QgsAbstractContentCacheBase | |
Protected Member Functions inherited from QgsAbstractContentCache< QgsImageCacheEntry > | |
QgsImageCacheEntry * | findExistingEntry (QgsImageCacheEntry *entryTemplate) |
Returns the existing entry from the cache which matches entryTemplate (deleting entryTemplate when done), or if no existing entry is found then entryTemplate is transferred to the cache and returned. | |
QByteArray | getContent (const QString &path, const QByteArray &missingContent, const QByteArray &fetchingContent, bool blocking=false) const |
Gets the file content corresponding to the given path. | |
void | onRemoteContentFetched (const QString &url, bool success) override |
Triggered after remote content (i.e. | |
void | trimToMaximumSize () |
Removes the least used cache entries until the maximum cache size is under the predefined size limit. | |
bool | waitForTaskFinished (QgsNetworkContentFetcherTask *task) const |
Blocks the current thread until the task finishes (or user's preset network timeout expires) | |
Protected Member Functions inherited from QgsAbstractContentCacheBase | |
virtual bool | checkReply (QNetworkReply *reply, const QString &path) const |
Runs additional checks on a network reply to ensure that the reply content is consistent with that required by the cache. | |
Protected Attributes inherited from QgsAbstractContentCache< QgsImageCacheEntry > | |
long | mMaxCacheSize |
Maximum cache size. | |
QRecursiveMutex | mMutex |
long | mTotalSize |
Estimated total size of all cached content. | |
A cache for images derived from raster files.
QgsImageCache stores pre-rendered resampled versions of raster image files, allowing efficient reuse without incurring the cost of resampling on every render.
QgsImageCache is not usually directly created, but rather accessed through QgsApplication::imageCache().
Definition at line 131 of file qgsimagecache.h.
QgsImageCache::QgsImageCache | ( | QObject * | parent = nullptr | ) |
Constructor for QgsImageCache, with the specified parent object.
Definition at line 92 of file qgsimagecache.cpp.
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Returns the maximum size of the cache, in bytes.
Definition at line 150 of file qgsimagecache.h.
int QgsImageCache::nextFrameDelay | ( | const QString & | path, |
int | currentFrame = 0 , |
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bool | blocking = false |
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For image formats that support animation, this function returns the number of milliseconds to wait until displaying the next frame in the animation.
If the image format doesn't support animation, 0 is returned.
path may be a local file, remote (HTTP) url, or a base 64 encoded string (with a "base64:" prefix).
If path is a remote file, then -1 may be returned while the image is in the process of being fetched.
The blocking boolean forces to wait for loading before returning the frame delay. The content is loaded in the same thread to ensure provided the original size. WARNING: the blocking parameter must NEVER be true
from GUI based applications (like the main QGIS application) or crashes will result. Only for use in external scripts or QGIS server.
If the image could not be read or is not an animated format then -1 is returned.
Definition at line 274 of file qgsimagecache.cpp.
QSize QgsImageCache::originalSize | ( | const QString & | path, |
bool | blocking = false |
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Returns the original size (in pixels) of the image at the specified path.
path may be a local file, remote (HTTP) url, or a base 64 encoded string (with a "base64:" prefix).
If path is a remote file, then an invalid size may be returned while the image is in the process of being fetched.
The blocking boolean forces to wait for loading before returning the original size. The content is loaded in the same thread to ensure provided the original size. WARNING: the blocking parameter must NEVER be true
from GUI based applications (like the main QGIS application) or crashes will result. Only for use in external scripts or QGIS server.
If the image could not be read then an invalid QSize is returned.
Definition at line 216 of file qgsimagecache.cpp.
QImage QgsImageCache::pathAsImage | ( | const QString & | path, |
const QSize | size, | ||
const bool | keepAspectRatio, | ||
const double | opacity, | ||
bool & | fitsInCache, | ||
bool | blocking = false , |
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double | targetDpi = 96 , |
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int | frameNumber = -1 , |
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bool * | isMissing = nullptr |
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Returns the specified path rendered as an image.
If possible, a pre-existing cached version of the image will be used. If not, the image is fetched and resampled to the desired size, and then the result cached for subsequent lookups.
path | may be a local file, remote (HTTP) url, or a base 64 encoded string (with a "base64:" prefix). |
size | dictates the target size of the image. An invalid size indicates the original raster image size (with no resampling). A size in which the width or height is set to zero will have the zeroed value automatically computed when keepAspectRatio is true . |
keepAspectRatio | if true then the original raster aspect ratio will be maintained during any resampling operations. |
opacity | dictates the opacity of the image (between 0 and 1). |
fitsInCache | will be set to true if the resultant raster was of a sufficiently small size to store in the cache |
blocking | if true , forces to wait for loading before returning image. The content is loaded in the same thread to ensure provided the image. WARNING: the blocking parameter must NEVER be true from GUI based applications (like the main QGIS application) or crashes will result. Only for use in external scripts or QGIS server. |
targetDpi | (since QGIS 3.22) can be used to specify an explicit DPI to render the image at. This is used for some image formats (e.g. PDF) to ensure that content is rendered at the desired DPI. This argument is only used when an invalid size argument is specified. If a valid size is specified then the image will always be rendered at this size, regardless of the targetDpi. |
frameNumber | (since QGIS 3.26) specifies a frame number for image formats which support animations. This should be set to -1 if not required. |
isMissing | will be set to true if returned image is the "broken" image placeholder |
Definition at line 138 of file qgsimagecache.cpp.
void QgsImageCache::prepareAnimation | ( | const QString & | path | ) |
Prepares for optimized retrieval of frames for the animation at the given path.
Definition at line 296 of file qgsimagecache.cpp.
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Emitted when the cache has finished retrieving an image file from a remote url.
int QgsImageCache::totalFrameCount | ( | const QString & | path, |
bool | blocking = false |
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Returns the total frame count of the image at the specified path.
path may be a local file, remote (HTTP) url, or a base 64 encoded string (with a "base64:" prefix).
If path is a remote file, then -1 may be returned while the image is in the process of being fetched.
The blocking boolean forces to wait for loading before returning the frame count. The content is loaded in the same thread to ensure provided the original size. WARNING: the blocking parameter must NEVER be true
from GUI based applications (like the main QGIS application) or crashes will result. Only for use in external scripts or QGIS server.
If the image could not be read or is not an animated format then -1 is returned
Definition at line 252 of file qgsimagecache.cpp.
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friend |
Definition at line 269 of file qgsimagecache.h.