feat(identicon): add algorithm to create identicons

ported from https://github.com/sudden6/rust-identicon/blob/master/src/lib.rs
but slightly changed the algorithm

CMakeLists.txt

@@ -413,6 +413,8 @@ set(${PROJECT_NAME}_SOURCES
   src/widget/tool/flyoutoverlaywidget.h
   src/widget/tool/friendrequestdialog.cpp
   src/widget/tool/friendrequestdialog.h
+  src/widget/tool/identicon.cpp
+  src/widget/tool/identicon.h
   src/widget/tool/movablewidget.cpp
   src/widget/tool/movablewidget.h
   src/widget/tool/profileimporter.cpp

src/widget/tool/identicon.cpp

@@ -0,0 +1,143 @@
+/*
+    Copyright © 2017 by The qTox Project Contributors
+
+    This file is part of qTox, a Qt-based graphical interface for Tox.
+
+    qTox is libre software: you can redistribute it and/or modify
+    it under the terms of the GNU General Public License as published by
+    the Free Software Foundation, either version 3 of the License, or
+    (at your option) any later version.
+
+    qTox is distributed in the hope that it will be useful,
+    but WITHOUT ANY WARRANTY; without even the implied warranty of
+    MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+    GNU General Public License for more details.
+
+    You should have received a copy of the GNU General Public License
+    along with qTox.  If not, see <http://www.gnu.org/licenses/>.
+*/
+
+#include "identicon.h"
+#include "src/core/toxpk.h"
+
+#include <cassert>
+
+#include <QColor>
+#include <QCryptographicHash>
+#include <QDebug>
+#include <QImage>
+
+// The following constants change the appearance of the identicon
+// they have been choosen by trying to make the output look nice.
+/**
+ * @var Identicon::IDENTICON_COLOR_BYTES
+ * Specifies how many bytes should define the foreground color
+ * must be smaller than 8, else there'll be overflows
+ */
+
+/**
+ * @var Identicon::COLORS
+ * Number of colors to use for the identicon
+ */
+
+/**
+ * @var Identicon::IDENTICON_ROWS
+ * Specifies how many rows of blocks the identicon should have
+ */
+
+/**
+ * @var Identicon::ACTIVE_COLS
+ * Width from the center to the outside, for 5 columns it's 3, 6 -> 3, 7 -> 4
+ */
+
+/**
+ * @var Identicon::HASH_MIN_LEN
+ * Min length of the hash in bytes, 7 bytes control the color,
+ * the rest controls the pixel placement
+ */
+
+/**
+ * @brief Creates an Identicon, that visualizes a hash in graphical form.
+ * @param data Data to visualize
+ */
+Identicon::Identicon(const QByteArray& data)
+{
+    static_assert(Identicon::COLORS == 2, "Only two colors are implemented");
+    // hash with sha256
+    QByteArray hash = QCryptographicHash::hash(data, QCryptographicHash::Sha256);
+    for (int colorIndex = 0; colorIndex < COLORS; ++colorIndex) {
+        const QByteArray hashPart = hash.right(IDENTICON_COLOR_BYTES);
+        hash.truncate(hash.length() - IDENTICON_COLOR_BYTES);
+
+        const qreal hue = bytesToColor(hashPart);
+        // change offset when COLORS != 2
+        const qreal lig = static_cast<qreal>(colorIndex) / COLORS + 0.3;
+        const qreal sat = 0.5;
+        colors[colorIndex].setHslF(hue, sat, lig);
+    }
+
+    const uint8_t* const hashBytes = reinterpret_cast<const uint8_t*>(hash.constData());
+    // compute the block colors from the hash
+    for (int row = 0; row < IDENTICON_ROWS; ++row) {
+        for (int col = 0; col < ACTIVE_COLS; ++col) {
+            const int hashIdx = row * ACTIVE_COLS + col;
+            const uint8_t colorIndex = hashBytes[hashIdx] % COLORS;
+            identiconColors[row][col] = colorIndex;
+        }
+    }
+}
+
+/**
+ * @brief Converts a series of IDENTICON_COLOR_BYTES bytes to a value in the range 0.0..1.0
+ * @param bytes Bytes to convert to a color
+ * @return Value in the range of 0.0..1.0
+ */
+float Identicon::bytesToColor(QByteArray bytes)
+{
+    static_assert(IDENTICON_COLOR_BYTES <= 8, "IDENTICON_COLOR max value is 8");
+    const uint8_t* const bytesChr = reinterpret_cast<const uint8_t*>(bytes.constData());
+    assert(bytes.length() == IDENTICON_COLOR_BYTES);
+
+    // get foreground color
+    uint64_t hue = bytesChr[0];
+
+    // convert the last bytes to an uint
+    for (int i = 1; i < IDENTICON_COLOR_BYTES; ++i) {
+        hue = hue << 8;
+        hue += bytesChr[i];
+    }
+
+    // normalize to 0.0 ... 1.0
+    return (static_cast<float>(hue))
+           / (((static_cast<uint64_t>(1)) << (8 * IDENTICON_COLOR_BYTES)) - 1);
+}
+
+/**
+ * @brief Writes the Identicon to a QImage
+ * @param scaleFactor the image will be a square with scaleFactor * IDENTICON_ROWS pixels,
+ *                    must be >= 1
+ * @return a QImage with the identicon
+ */
+QImage Identicon::toImage(int scaleFactor)
+{
+    if (scaleFactor < 1) {
+        qDebug() << "Can't scale with values <1, clamping to 1";
+        scaleFactor = 1;
+    }
+
+    scaleFactor *= IDENTICON_ROWS;
+
+    QImage pixels(IDENTICON_ROWS, IDENTICON_ROWS, QImage::Format_RGB888);
+
+    for (int row = 0; row < IDENTICON_ROWS; ++row) {
+        for (int col = 0; col < IDENTICON_ROWS; ++col) {
+            // mirror on vertical axis
+            const int columnIdx = abs((col * 2 - (IDENTICON_ROWS - 1)) / 2);
+            const int colorIdx = identiconColors[row][columnIdx];
+            pixels.setPixel(col, row, colors[colorIdx].rgb());
+        }
+    }
+
+    // scale up without smoothing to make it look sharp
+    return pixels.scaled(scaleFactor, scaleFactor, Qt::IgnoreAspectRatio, Qt::FastTransformation);
+}

src/widget/tool/identicon.h

@@ -0,0 +1,30 @@
+#ifndef IDENTICON_H
+#define IDENTICON_H
+
+#include <QColor>
+#include <QImage>
+
+class Identicon
+{
+public:
+    Identicon(const QByteArray& data);
+    QImage toImage(int scaleFactor = 1);
+
+public:
+    static constexpr int IDENTICON_ROWS = 5;
+
+private:
+    float bytesToColor(QByteArray bytes);
+
+private:
+    static constexpr int COLORS = 2;
+    static constexpr int ACTIVE_COLS = (IDENTICON_ROWS + 1) / 2;
+    static constexpr int IDENTICON_COLOR_BYTES = 6;
+    static constexpr int HASH_MIN_LEN = ACTIVE_COLS * IDENTICON_ROWS
+                                      + COLORS * IDENTICON_COLOR_BYTES;
+
+    uint8_t identiconColors[IDENTICON_ROWS][ACTIVE_COLS];
+    QColor colors[COLORS];
+};
+
+#endif // IDENTICON_H