Make scaled image size calculation available to image providers

When reduced size image loading is requested through
Image::sourceSize, the precise calculation of the scaled size to load
is somewhat complex. This commit moves that calculation into a function
accessible to image providers, so that they may use the same scaling
as Quick's default image loading, and avoid code duplication.

This is a code restructuring only; no behavior should change.

Change-Id: Ic965fb2b6c22a5d21add41b8395e3a3842697d20
Reviewed-by: Shawn Rutledge <shawn.rutledge@qt.io>

1 files changed, 36 insertions, 1 deletions

diff --git a/src/quick/util/qquickimageprovider.cpp b/src/quick/util/qquickimageprovider.cpp
index a026abe762..56b2d7070d 100644
--- a/src/quick/util/qquickimageprovider.cpp
+++ b/src/quick/util/qquickimageprovider.cpp
@@ -603,7 +603,6 @@ void QQuickImageProviderOptions::setPreserveAspectRatioFit(bool preserveAspectRa
     d->preserveAspectRatioFit = preserveAspectRatioFit;
 }
 
-
 QQuickImageProviderWithOptions::QQuickImageProviderWithOptions(ImageType type, Flags flags)
  : QQuickAsyncImageProvider()
 {
@@ -660,5 +659,41 @@ QQuickImageResponse *QQuickImageProviderWithOptions::requestImageResponse(const
     return requestImageResponse(id, requestedSize);
 }
 
+/*!
+    Returns the recommended scaled image size for loading and storage. This is
+    calculated according to the native pixel size of the image \a originalSize,
+    the requested sourceSize \a requestedSize, the image file format \a format,
+    and \a options. If the calculation otherwise concludes that scaled loading
+    is not recommended, an invalid size is returned.
+*/
+QSize QQuickImageProviderWithOptions::loadSize(const QSize &originalSize, const QSize &requestedSize, const QByteArray &format, const QQuickImageProviderOptions &options)
+{
+    QSize res;
+    if ((requestedSize.width() <= 0 && requestedSize.height() <= 0) || originalSize.isEmpty())
+        return res;
+
+    const bool preserveAspectCropOrFit = options.preserveAspectRatioCrop() || options.preserveAspectRatioFit();
+    const bool force_scale = (format == "svg" || format == "svgz");
+
+    qreal ratio = 0.0;
+    if (requestedSize.width() && (preserveAspectCropOrFit || force_scale || requestedSize.width() < originalSize.width())) {
+        ratio = qreal(requestedSize.width()) / originalSize.width();
+    }
+    if (requestedSize.height() && (preserveAspectCropOrFit || force_scale || requestedSize.height() < originalSize.height())) {
+        qreal hr = qreal(requestedSize.height()) / originalSize.height();
+        if (ratio == 0.0)
+            ratio = hr;
+        else if (!preserveAspectCropOrFit && (hr < ratio))
+            ratio = hr;
+        else if (preserveAspectCropOrFit && (hr > ratio))
+            ratio = hr;
+    }
+    if (ratio > 0.0) {
+        res.setHeight(qRound(originalSize.height() * ratio));
+        res.setWidth(qRound(originalSize.width() * ratio));
+    }
+    return res;
+}
+
 QT_END_NAMESPACE