add image interface, remove lodepng from video_core/core, address more comments, fix comments

remove unnecessary conversion

src/citra_qt/qt_image_interface.cpp

@@ -0,0 +1,46 @@
+// Copyright 2019 Citra Emulator Project
+// Licensed under GPLv2 or any later version
+// Refer to the license.txt file included.
+
+#include <QBuffer>
+#include <QImage>
+#include <QString>
+#include "common/logging/log.h"
+#include "core/frontend/image_interface.h"
+#include "qt_image_interface.h"
+
+bool QtImageInterface::DecodePNG(std::vector<u8>& dst, u32& width, u32& height,
+                                 const std::string& path) {
+    QImage image(QString::fromStdString(path));
+
+    if (image.isNull()) {
+        LOG_ERROR(Frontend, "Failed to open {} for decoding", path);
+        return false;
+    }
+    width = image.width();
+    height = image.height();
+
+    // Write RGBA8 to vector
+    for (u32 y = 1; y < image.height() + 1; y++) {
+        for (u32 x = 1; x < image.width() + 1; x++) {
+            const QColor pixel(image.pixel(y, x));
+            dst.push_back(pixel.red());
+            dst.push_back(pixel.green());
+            dst.push_back(pixel.blue());
+            dst.push_back(pixel.alpha());
+        }
+    }
+
+    return true;
+}
+
+bool QtImageInterface::EncodePNG(const std::string& path, const std::vector<u8>& src, u32 width,
+                                 u32 height) {
+    QImage image(src.data(), width, height, QImage::Format_RGBA8888);
+
+    if (!image.save(QString::fromStdString(path))) {
+        LOG_ERROR(Frontend, "Failed to save {}", path);
+        return false;
+    }
+    return true;
+}