feat: Add --dark flag to iv for Dark Mode

Add a --dark CLI argument that activates dark mode using Qt's Fusion style
with a custom dark QPalette. The flag integrates with the existing
darkPalette preference system in ImageViewer, so both the --dark CLI flag
and the Preferences checkbox produce the same result.

The dark palette is applied inside ImageViewer's constructor (rather than
in main()) so it does not conflict with ImageViewer's own palette setup.
The OpenGL background for transparent pixels (glClearColor) is unaffected
since it is hardcoded separately from the QPalette.

Signed-off-by: Shashvat Singh <shashvat.kk@gmail.com>
Signed-off-by: sh4shv4t <shashvat.k.singh.16@gmail.com>

Author: sh4shv4t

src/iv/imageviewer.cpp

@@ -25,11 +25,13 @@
 #include <QMenu>
 #include <QMenuBar>
 #include <QMessageBox>
+#include <QPalette>
 #include <QProgressBar>
 #include <QResizeEvent>
 #include <QSettings>
 #include <QSpinBox>
 #include <QStatusBar>
+#include <QStyleFactory>
 #include <QTimer>
 
 #if OIIO_QT_MAJOR < 6
@@ -99,7 +101,8 @@ static const char *s_file_filters = ""
 
 
 ImageViewer::ImageViewer(bool use_ocio, const std::string& image_color_space,
-                         const std::string& display, const std::string& view)
+                         const std::string& display, const std::string& view,
+                         bool dark)
     : infoWindow(NULL)
     , preferenceWindow(NULL)
     , darkPaletteBox(NULL)
@@ -110,7 +113,7 @@ ImageViewer::ImageViewer(bool use_ocio, const std::string& image_color_space,
     , m_zoom(1)
     , m_fullscreen(false)
     , m_default_gamma(1)
-    , m_darkPalette(false)
+    , m_darkPalette(dark)
     , m_useOCIO(use_ocio)
     , m_ocioColourSpace(image_color_space)
     , m_ocioDisplay(display)
@@ -126,10 +129,26 @@ ImageViewer::ImageViewer(bool use_ocio, const std::string& image_color_space,
     // Also, some time in the future we may want a real 3D LUT for
     // "film look", etc.
 
-    if (darkPalette())
-        m_palette = QPalette(Qt::darkGray);  // darkGray?
-    else
+    if (darkPalette()) {
+        QApplication::setStyle(QStyleFactory::create("Fusion"));
+        QPalette dp;
+        dp.setColor(QPalette::Window, QColor(53, 53, 53));
+        dp.setColor(QPalette::WindowText, Qt::white);
+        dp.setColor(QPalette::Base, QColor(25, 25, 25));
+        dp.setColor(QPalette::AlternateBase, QColor(53, 53, 53));
+        dp.setColor(QPalette::ToolTipBase, Qt::white);
+        dp.setColor(QPalette::ToolTipText, Qt::white);
+        dp.setColor(QPalette::Text, Qt::white);
+        dp.setColor(QPalette::Button, QColor(53, 53, 53));
+        dp.setColor(QPalette::ButtonText, Qt::white);
+        dp.setColor(QPalette::BrightText, Qt::red);
+        dp.setColor(QPalette::Link, QColor(42, 130, 218));
+        dp.setColor(QPalette::Highlight, QColor(42, 130, 218));
+        dp.setColor(QPalette::HighlightedText, Qt::black);
+        m_palette = dp;
+    } else {
         m_palette = QPalette();
+    }
     QApplication::setPalette(m_palette);  // FIXME -- why not work?
     this->setPalette(m_palette);
 

src/iv/imageviewer.h

@@ -148,7 +148,8 @@ class ImageViewer final : public QMainWindow {
 
 public:
     ImageViewer(bool use_ocio, const std::string& image_color_space,
-                const std::string& display, const std::string& view);
+                const std::string& display, const std::string& view,
+                bool dark = false);
     ~ImageViewer();
 
     enum COLOR_MODE {

src/iv/ivmain.cpp

@@ -58,6 +58,11 @@ getargs(int argc, char* argv[])
     ap.arg("--rawcolor")
       .help("Do not automatically transform to RGB");
 
+    ap.arg("--dark")
+      .help("Start in dark mode")
+      .dest("dark")
+      .store_true();
+
     ap.arg("--display")
       .help("OCIO display")
       .metavar("STRING")
@@ -124,8 +129,8 @@ main(int argc, char* argv[])
 #endif
     }
 
-    ImageViewer* mainWin = new ImageViewer(use_ocio, color_space, display,
-                                           view);
+    ImageViewer* mainWin = new ImageViewer(use_ocio, color_space, display, view,
+                                           ap["dark"].get<int>());
 
     mainWin->show();