Add a new module for resizing images including Lanczos

image_processing/resize_image.cpp

@@ -0,0 +1,60 @@
+#include "resize_image.h"
+
+#include "lancir.h"
+
+static QImage scaleImageLancir(const QImage &image, int width, int height)
+{
+    QImage src = (image.format() == QImage::Format_ARGB32)
+            ? image
+            : image.convertToFormat(QImage::Format_ARGB32);
+
+    QImage dst(width, height, QImage::Format_ARGB32);
+
+    // SrcSSize / NewSSize are in elements; for uint8_t that equals bytes,
+    // so bytesPerLine() covers any Qt row-alignment padding correctly.
+    avir::CLancIRParams params(src.bytesPerLine(), dst.bytesPerLine());
+    params.la = 4.0; // Lanczos4
+
+    avir::CLancIR lancir;
+    lancir.resizeImage<uint8_t, uint8_t>(
+            src.constBits(), src.width(), src.height(),
+            dst.bits(), width, height, 4, &params);
+
+    return dst;
+}
+
+// ---- QPixmap API ------------------------------------------------------------
+
+QPixmap scalePixmap(const QPixmap &pixmap, int width, int height, ScaleMethod method)
+{
+    if ((pixmap.width() == width && pixmap.height() == height) || pixmap.isNull())
+        return pixmap;
+
+    switch (method) {
+    case ScaleMethod::Nearest:
+        return pixmap.scaled(width, height, Qt::IgnoreAspectRatio, Qt::FastTransformation);
+    case ScaleMethod::Bilinear:
+        return pixmap.scaled(width, height, Qt::IgnoreAspectRatio, Qt::SmoothTransformation);
+    case ScaleMethod::Lanczos:
+        return QPixmap::fromImage(scaleImageLancir(pixmap.toImage(), width, height));
+    }
+    return pixmap;
+}
+
+// ---- QImage API (avoids QPixmap round-trip in ContinuousPageWidget) ---------
+
+QImage scaleImage(const QImage &image, int width, int height, ScaleMethod method)
+{
+    if ((image.width() == width && image.height() == height) || image.isNull())
+        return image;
+
+    switch (method) {
+    case ScaleMethod::Nearest:
+        return image.scaled(width, height, Qt::IgnoreAspectRatio, Qt::FastTransformation);
+    case ScaleMethod::Bilinear:
+        return image.scaled(width, height, Qt::IgnoreAspectRatio, Qt::SmoothTransformation);
+    case ScaleMethod::Lanczos:
+        return scaleImageLancir(image, width, height);
+    }
+    return image;
+}