1 files changed, 58 insertions, 1 deletions

diff --git a/saltoqd/msolimageiohandler.cpp b/saltoqd/msolimageiohandler.cpp
index e6a9065..5a18ff6 100644
--- a/saltoqd/msolimageiohandler.cpp
+++ b/saltoqd/msolimageiohandler.cpp
@@ -21,6 +21,17 @@ static inline QRgb decode_color(uchar p, uchar a = 255)
 	return qRgba(p & 0xC0, (p & 0x30) << 2, (p & 0x0C) << 4, a);
 }
 
+static inline uchar add_saturate(uchar val, int addend)
+{
+	int sum = val + addend;
+	return qMax(0, qMin(sum, 255));
+}
+
+static inline void add_saturate(uchar* val, int addend)
+{
+	*val = add_saturate(*val, addend);
+}
+
 }
 
 MSOLImageIOHandler::MSOLImageIOHandler() : QImageIOHandler()
@@ -93,6 +104,7 @@ bool MSOLImageIOHandler::write(const QImage &image)
 	const int line_size = width * pixel_size;
 
 	QImage img = image.convertToFormat(alpha ? QImage::Format_ARGB32 : QImage::Format_RGB32);
+	img = ditherForMsol(img);
 
 	uchar header[header_size] = { 0 };
 	strcpy(reinterpret_cast<char*>(&header[0]), "MSOL  ");
@@ -159,7 +171,8 @@ QVariant MSOLImageIOHandler::option(ImageOption option) const
 
 void MSOLImageIOHandler::setOption(ImageOption option, const QVariant &value)
 {
-
+	Q_UNUSED(option);
+	Q_UNUSED(value);
 }
 
 QByteArray convertImageToMsol(const QImage &img)
@@ -186,3 +199,47 @@ QImage convertMsolToImage(const QByteArray &msol)
 	}
 	return img;
 }
+
+QImage ditherForMsol(const QImage &src)
+{
+	Q_ASSERT(src.format() == QImage::Format_ARGB32 || src.format() == QImage::Format_RGB32);
+	const int width = src.width(), height = src.height();
+	const int bytesPerLine = src.bytesPerLine();
+
+	QImage dst(src);
+
+	// If we are on Big endian, then we must skip the first channel (=alpha).
+	// In LE, use the first three channels and skip the final one (=alpha).
+	const bool bigEndian = QSysInfo::ByteOrder == QSysInfo::BigEndian;
+	uchar *line = dst.bits() + (bigEndian ? 1 : 0);
+	for (int y = 0; y < height; y++) {
+		for (int x = 0; x < width; x++) {
+			for (int chan = 0; chan < 3; chan++) {
+				const uchar val = line[x * 4 + chan];
+				const uchar quant = add_saturate(val, 0x20) & 0xC0;
+				const int error = val - quant;
+
+				line[x * 4 + chan] = quant;
+
+				if (x + 1 < width)
+					add_saturate(&line[(x + 1) * 4 + chan], (error * 7) / 16);
+
+				if (y + 1 < height) {
+					uchar *nextLine = line + bytesPerLine;
+
+					if (x > 0)
+						add_saturate(&nextLine[(x - 1) * 4 + chan], (error * 3) / 16);
+
+					add_saturate(&nextLine[x * 4 + chan], (error * 5) / 16);
+
+					if (x + 1 < width)
+						add_saturate(&nextLine[(x + 1) * 4 + chan], (error * 1) / 16);
+				}
+			}
+		}
+
+		line += bytesPerLine;
+	}
+
+	return dst;
+}