Add a class derived from GtkImage to support HiDPI bitmaps

And use it to get HiDPI support wherever we use GtkImage. This extends and
consolidates support for custom drawing of images which has already been added
somewhat redundantly in several places.

src/gtk/image_gtk.cpp

@@ -0,0 +1,169 @@
+///////////////////////////////////////////////////////////////////////////////
+// Name:        src/gtk/image_gtk.cpp
+// Author:      Paul Cornett
+// Copyright:   (c) 2020 Paul Cornett
+// Licence:     wxWindows licence
+///////////////////////////////////////////////////////////////////////////////
+
+#include "wx/wxprec.h"
+
+#include "wx/bitmap.h"
+#include "wx/window.h"
+
+#include "wx/gtk/private/wrapgtk.h"
+#include "wx/gtk/private/image.h"
+
+namespace
+{
+// Default provider for HiDPI common case
+struct BitmapProviderDefault: wxGtkImage::BitmapProvider
+{
+#ifdef __WXGTK3__
+    BitmapProviderDefault(wxWindow* win) : m_win(win) { }
+    virtual wxBitmap Get() const wxOVERRIDE;
+    virtual void Set(const wxBitmap& bitmap) wxOVERRIDE;
+    wxWindow* const m_win;
+    wxBitmap m_bitmap;
+    wxBitmap m_bitmapDisabled;
+#else
+    BitmapProviderDefault(wxWindow*) { }
+    virtual wxBitmap Get() const wxOVERRIDE { return wxBitmap(); }
+#endif
+};
+
+#ifdef __WXGTK3__
+wxBitmap BitmapProviderDefault::Get() const
+{
+    return (m_win == NULL || m_win->IsEnabled()) ? m_bitmap : m_bitmapDisabled;
+}
+
+void BitmapProviderDefault::Set(const wxBitmap& bitmap)
+{
+    m_bitmap.UnRef();
+    m_bitmapDisabled.UnRef();
+    if (bitmap.IsOk() && bitmap.GetScaleFactor() > 1)
+    {
+        m_bitmap = bitmap;
+        if (m_win)
+            m_bitmapDisabled = bitmap.CreateDisabled();
+    }
+}
+#endif // __WXGTK3__
+} // namespace
+
+extern "C" {
+static void wxGtkImageClassInit(void* g_class, void* class_data);
+}
+
+GType wxGtkImage::Type()
+{
+    static GType type;
+    if (type == 0)
+    {
+        const GTypeInfo info = {
+            sizeof(GtkImageClass),
+            NULL, NULL,
+            wxGtkImageClassInit, NULL, NULL,
+            sizeof(wxGtkImage), 0, NULL,
+            NULL
+        };
+        type = g_type_register_static(
+            GTK_TYPE_IMAGE, "wxGtkImage", &info, GTypeFlags(0));
+    }
+    return type;
+}
+
+GtkWidget* wxGtkImage::New(BitmapProvider* provider)
+{
+    wxGtkImage* image = WX_GTK_IMAGE(g_object_new(Type(), NULL));
+    image->m_provider = provider;
+    return GTK_WIDGET(image);
+}
+
+GtkWidget* wxGtkImage::New(wxWindow* win)
+{
+    return New(new BitmapProviderDefault(win));
+}
+
+void wxGtkImage::Set(const wxBitmap& bitmap)
+{
+    m_provider->Set(bitmap);
+
+    GdkPixbuf* pixbuf = NULL;
+    GdkPixbuf* pixbufNew = NULL;
+    if (bitmap.IsOk())
+    {
+        if (bitmap.GetScaleFactor() <= 1)
+            pixbuf = bitmap.GetPixbuf();
+        else
+        {
+            // Placeholder pixbuf for correct size
+            pixbufNew =
+            pixbuf = gdk_pixbuf_new(GDK_COLORSPACE_RGB, false, 8,
+                int(bitmap.GetScaledWidth()), int(bitmap.GetScaledHeight()));
+        }
+    }
+    gtk_image_set_from_pixbuf(GTK_IMAGE(this), pixbuf);
+    if (pixbufNew)
+        g_object_unref(pixbufNew);
+}
+
+static GtkWidgetClass* wxGtkImageParentClass;
+
+extern "C"
+{
+#ifdef __WXGTK3__
+static gboolean wxGtkImageDraw(GtkWidget* widget, cairo_t* cr)
+#else
+static gboolean wxGtkImageDraw(GtkWidget* widget, GdkEventExpose* event)
+#endif
+{
+    wxGtkImage* image = WX_GTK_IMAGE(widget);
+    const wxBitmap bitmap(image->m_provider->Get());
+    if (!bitmap.IsOk())
+    {
+#ifdef __WXGTK3__
+        return wxGtkImageParentClass->draw(widget, cr);
+#else
+        return wxGtkImageParentClass->expose_event(widget, event);
+#endif
+    }
+
+    GtkAllocation alloc;
+    gtk_widget_get_allocation(widget, &alloc);
+    int x = (alloc.width  - int(bitmap.GetScaledWidth() )) / 2;
+    int y = (alloc.height - int(bitmap.GetScaledHeight())) / 2;
+#ifdef __WXGTK3__
+    gtk_render_background(gtk_widget_get_style_context(widget),
+        cr, 0, 0, alloc.width, alloc.height);
+    bitmap.Draw(cr, x, y);
+#else
+    x += alloc.x;
+    y += alloc.y;
+    gdk_draw_pixbuf(
+        gtk_widget_get_window(widget), gtk_widget_get_style(widget)->black_gc, bitmap.GetPixbuf(),
+        0, 0, x, y,
+        -1, -1, GDK_RGB_DITHER_NORMAL, 0, 0);
+#endif
+    return false;
+}
+
+static void wxGtkImageFinalize(GObject* object)
+{
+    wxGtkImage* image = WX_GTK_IMAGE(object);
+    delete image->m_provider;
+    image->m_provider = NULL;
+    G_OBJECT_CLASS(wxGtkImageParentClass)->finalize(object);
+}
+
+static void wxGtkImageClassInit(void* g_class, void* /*class_data*/)
+{
+#ifdef __WXGTK3__
+    GTK_WIDGET_CLASS(g_class)->draw = wxGtkImageDraw;
+#else
+    GTK_WIDGET_CLASS(g_class)->expose_event = wxGtkImageDraw;
+#endif
+    G_OBJECT_CLASS(g_class)->finalize = wxGtkImageFinalize;
+    wxGtkImageParentClass = GTK_WIDGET_CLASS(g_type_class_peek_parent(g_class));
+}
+} // extern "C"