1 files changed, 80 insertions, 0 deletions
diff --git a/src/ui/widget/optglarea.h b/src/ui/widget/optglarea.h
new file mode 100644
index 0000000..fa71afc
--- /dev/null
+++ b/src/ui/widget/optglarea.h
@@ -0,0 +1,80 @@
+// SPDX-License-Identifier: GPL-2.0-or-later
+#ifndef INKSCAPE_UI_WIDGET_OPTGLAREA_H
+#define INKSCAPE_UI_WIDGET_OPTGLAREA_H
+
+#include <gtkmm.h>
+#include <epoxy/gl.h>
+
+namespace Cairo {
+class Context;
+}
+
+namespace Inkscape {
+namespace UI {
+namespace Widget {
+
+/**
+ * A widget that can dynamically switch between a Gtk::DrawingArea and a Gtk::GLArea.
+ * Based on the GTK source code for both widgets.
+ */
+class OptGLArea : public Gtk::DrawingArea
+{
+public:
+    OptGLArea();
+
+    /**
+     * Set whether OpenGL is enabled. Initially it is disabled. Upon enabling it,
+     * create_context will be called as soon as the widget is realized. If
+     * context creation fails, OpenGL will be disabled again.
+     */
+    void set_opengl_enabled(bool);
+    bool get_opengl_enabled() const { return opengl_enabled; }
+
+    /**
+     * Call before doing any OpenGL operations to make the context current.
+     * Automatically done before calling opengl_render.
+     */
+    void make_current();
+
+    /**
+     * Call before rendering to the widget to bind the widget's framebuffer.
+     */
+    void bind_framebuffer() const;
+
+protected:
+    void on_realize() override;
+    void on_unrealize() override;
+    void on_size_allocate(Gtk::Allocation&) override;
+    bool on_draw(const Cairo::RefPtr<Cairo::Context>&) final;
+
+    /**
+     * Reimplement to create the desired OpenGL context. Return nullptr on error.
+     */
+    virtual Glib::RefPtr<Gdk::GLContext> create_context() = 0;
+
+    /**
+     * Reimplement to render the widget. The Cairo context is only for when OpenGL is disabled.
+     */
+    virtual void paint_widget(const Cairo::RefPtr<Cairo::Context>&) {}
+
+private:
+    void init_opengl();
+    void create_framebuffer();
+    void delete_framebuffer();
+    void resize_framebuffer() const;
+
+    Glib::RefPtr<Gdk::GLContext> context;
+
+    bool opengl_enabled;
+    bool need_resize;
+
+    GLuint framebuffer;
+    GLuint renderbuffer;
+    GLuint stencilbuffer;
+};
+
+} // namespace Widget
+} // namespace UI
+} // namespace Inkscape
+
+#endif // INKSCAPE_UI_WIDGET_OPTGLAREA_H