exr: write support and more

- Added support for writing EXR files
- Large image support (tested with 32GiB 16-bit image)
- OpenEXR multithreaded read/write support through the use of line blocks
- Build option to enable conversion to sRGB when read (disabled by default)
- Multi-view image reading support
- Options support: Size, ImageFormat, Quality, CompressRatio
- Metadata write/read support via EXR attributes

The plugin is now quite complete. It should also work on KF5 (not tested): if there is the will to include this MR also on KF5, let me know and I will do all the necessary tests.

src/imageformats/exr_p.h

@@ -1,8 +1,8 @@
 /*
-    QImageIO Routines to read (and perhaps in the future, write) images
-    in the high definition EXR format.
+    The high dynamic range EXR format support for QImage.
 
     SPDX-FileCopyrightText: 2003 Brad Hards <bradh@frogmouth.net>
+    SPDX-FileCopyrightText: 2023 Mirco Miranda <mircomir@outlook.com>
 
     SPDX-License-Identifier: LGPL-2.0-or-later
 */
@@ -12,6 +12,44 @@
 
 #include <QImageIOPlugin>
 
+/*!
+ * \brief The EXRHandler class
+ * The handler uses the OpenEXR reference implementation of the EXR file format.
+ *
+ * The purpose of EXR format is to accurately and efficiently represent high-dynamic-range scene-linear
+ * image data and associated metadata.
+ *
+ * Both reading and writing of EXR files is supported. When saving, the image is converted to 16-bit
+ * and sRGB Linear color space (if not already so). If no color space is set in the image, sRGB is assumed.
+ * When the handler is compiled with the default compile options, the loaded image is a 16-bit image
+ * with linear color space.
+ * Multiview images are also supported (read only) via imageCount(), jumpToImage(), etc....
+ *
+ * The following QImageIOHandler options are supported:
+ * - ImageFormat: The image's data format returned by the handler.
+ * - Size: The size of the image.
+ * - CompressionRatio: The compression ratio of the image data (see OpenEXR compression schemes).
+ * - Quality: The quality level of the image (see OpenEXR compression level of lossy codecs).
+ *
+ * The following metadata are set/get via QImage::setText()/QImage::text() in both read/write (if any):
+ * - Latitude, Longitude, Altitude: Geographic coordinates (Float converted to string).
+ * - CreationDate: Date the image was captured/created (QDateTime converted to string using Qt::ISODate).
+ * - Comment: Additional image information in human-readable form, for example a verbal description of the image (QString).
+ * - Owner: Name of the owner of the image (QString).
+ *
+ * In addition, information about image resolution is preserved and the preview is written for images larger
+ * than 1024px.
+ *
+ * The following compile options are supported (defines):
+ * - EXR_MAX_IMAGE_WIDTH: Maximum image width supported (read/write, default: 300000 px).
+ * - EXR_MAX_IMAGE_HEIGHT: Maximum image height supported (read/write, default: 300000 px).
+ * - EXR_LINES_PER_BLOCK: The number of scanlines buffered on both read and write operations.\n
+ *                        The higher the value, the greater the parallelization but the RAM consumption increases (default: 128)
+ * - EXR_USE_LEGACY_CONVERSIONS: The result image is an 8-bit RGB(A) converted without icc profiles (read, default: undefined).
+ * - EXR_CONVERT_TO_SRGB: The resulting image is convertef in the sRGB color space (read, default: undefined).
+ * - EXR_DISABLE_XMP_ATTRIBUTE: Disable the stores of XMP values in a non-standard attribute named "xmp".\n
+ *                              The QImage metadata used is "XML:com.adobe.xmp" (write, default: undefined).
+ */
 class EXRHandler : public QImageIOHandler
 {
 public:
@@ -19,8 +57,65 @@ public:
 
     bool canRead() const override;
     bool read(QImage *outImage) override;
+    bool write(const QImage &image) override;
+
+    void setOption(ImageOption option, const QVariant &value) override;
+    bool supportsOption(QImageIOHandler::ImageOption option) const override;
+    QVariant option(QImageIOHandler::ImageOption option) const override;
+
+    bool jumpToNextImage() override;
+    bool jumpToImage(int imageNumber) override;
+    int imageCount() const override;
+    int currentImageNumber() const override;
 
     static bool canRead(QIODevice *device);
+
+private:
+    /*!
+     * \brief m_compressionRatio
+     * Value set by QImageWriter::setCompression().
+     *
+     * The compression scheme is the same as defined by OpenEXR library:
+     * - 0: no compression
+     * - 1: run length encoding
+     * - 2: zlib compression, one scan line at a time
+     * - 3: zlib compression, in blocks of 16 scan lines
+     * - 4: piz-based wavelet compression (default)
+     * - 5: lossy 24-bit float compression
+     * - 6: lossy 4-by-4 pixel block compression, fixed compression rate
+     * - 7: lossy 4-by-4 pixel block compression, fields are compressed more
+     * - 8: lossy DCT based compression, in blocks of 32 scanlines. More efficient for partial buffer access.
+     * - 9: lossy DCT based compression, in blocks of 256 scanlines. More efficient space wise and faster to decode full frames than DWAA_COMPRESSION.
+     */
+    qint32 m_compressionRatio;
+
+    /*!
+     * \brief m_quality
+     * Value set by QImageWriter::setQuality().
+     *
+     * The quality is used on DCT compression schemes only with a
+     * supposed value between 0 and 100 (default: 45).
+     */
+    qint32 m_quality;
+
+    /*!
+     * \brief m_imageNumber
+     * Value set by QImageReader::jumpToImage() or QImageReader::jumpToNextImage().
+     * The number of view selected in a multiview image.
+     */
+    qint32 m_imageNumber;
+
+    /*!
+     * \brief m_imageCount
+     * The total number of views (cache value)
+     */
+    mutable qint32 m_imageCount;
+
+    /*!
+     * \brief m_startPos
+     * The initial device position to allow multi image load (cache value).
+     */
+    qint64 m_startPos;
 };
 
 class EXRPlugin : public QImageIOPlugin