Add generic inplace converter

The generic converter can easily be modified to work inplace. Such
an inplace converter can ensure we can do direct conversion between
formats of similar pixel depth.

Inplace conversion is currently only used by QPixmaps, but will be used
by ref qualified versions of QImage::convertToFormat in a future patch.

Change-Id: Idbdaf087b53deecdee8258ba0b5d80edd37cfe79
Reviewed-by: Gunnar Sletta <gunnar.sletta@jollamobile.com>

src/gui/image/qimage.cpp

@@ -4424,6 +4424,8 @@ bool QImageData::convertInPlace(QImage::Format newFormat, Qt::ImageConversionFla
     InPlace_Image_Converter converter = *converterPtr;
     if (converter)
         return converter(this, flags);
+    else if (format > QImage::Format_Indexed8 && newFormat > QImage::Format_Indexed8)
+        return convert_generic_inplace(this, newFormat, flags);
     else
         return false;
 }

src/gui/image/qimage_conversions.cpp

@@ -138,6 +138,40 @@ void convert_generic(QImageData *dest, const QImageData *src, Qt::ImageConversio
     }
 }
 
+// Cannot be used with indexed formats or between formats with different pixel depths.
+bool convert_generic_inplace(QImageData *data, QImage::Format dst_format, Qt::ImageConversionFlags)
+{
+    Q_ASSERT(dst_format > QImage::Format_Indexed8);
+    Q_ASSERT(data->format > QImage::Format_Indexed8);
+    if (data->depth != qt_depthForFormat(dst_format))
+        return false;
+
+    const int buffer_size = 2048;
+    uint buffer[buffer_size];
+    const QPixelLayout *srcLayout = &qPixelLayouts[data->format];
+    const QPixelLayout *destLayout = &qPixelLayouts[dst_format];
+
+    uchar *srcData = data->data;
+
+    FetchPixelsFunc fetch = qFetchPixels[srcLayout->bpp];
+    StorePixelsFunc store = qStorePixels[destLayout->bpp];
+
+    for (int y = 0; y < data->height; ++y) {
+        int x = 0;
+        while (x < data->width) {
+            int l = qMin(data->width - x, buffer_size);
+            const uint *ptr = fetch(buffer, srcData, x, l);
+            ptr = srcLayout->convertToARGB32PM(buffer, ptr, l, srcLayout, 0);
+            ptr = destLayout->convertFromARGB32PM(buffer, ptr, l, destLayout, 0);
+            store(srcData, ptr, x, l);
+            x += l;
+        }
+        srcData += data->bytes_per_line;
+    }
+    data->format = dst_format;
+    return true;
+}
+
 static void convert_ARGB_to_ARGB_PM(QImageData *dest, const QImageData *src, Qt::ImageConversionFlags)
 {
     Q_ASSERT(src->format == QImage::Format_ARGB32 || src->format == QImage::Format_RGBA8888);

src/gui/image/qimage_p.h

@@ -115,6 +115,7 @@ extern Image_Converter qimage_converter_map[QImage::NImageFormats][QImage::NImag
 extern InPlace_Image_Converter qimage_inplace_converter_map[QImage::NImageFormats][QImage::NImageFormats];
 
 void convert_generic(QImageData *dest, const QImageData *src, Qt::ImageConversionFlags);
+bool convert_generic_inplace(QImageData *data, QImage::Format dst_format, Qt::ImageConversionFlags);
 
 void dither_to_Mono(QImageData *dst, const QImageData *src, Qt::ImageConversionFlags flags, bool fromalpha);