Add C++ API and example for borrowing OpenGL textures

api/cpp/include/slint_image.h

@@ -68,6 +68,42 @@ private:
     SharedVector<Pixel> m_data;
 };
 
+/// This structure contains fields to identify and render an OpenGL texture that Slint borrows from
+/// the applicatin code. Use this to embed a native OpenGL texture into a Slint scene, by
+/// constructing the `BorrowedOpenGLTexture` and then a `Image` from it.
+///
+/// The ownership of the texture remains with the application. It is the application's
+/// responsibility to delete the texture when it is not used anymore.
+///
+/// Note that only 2D RGBA textures are supported.
+struct BorrowedOpenGLTexture
+{
+public:
+    BorrowedOpenGLTexture() = delete;
+    /// Constructs a new BorrowedOpenGLTexture with the given \a texture_id and \a size. The \a
+    /// texture_id and \a size must be non-zero. The underlying texture must be a 2D RGBA texture
+    /// and ownership remains with the caller.
+    BorrowedOpenGLTexture(uint32_t texture_id, Size<unsigned int> size) : inner { texture_id, size }
+    {
+    }
+
+    /// Returns the OpenGL texture id.
+    uint32_t texture_id() const { return inner.texture_id; }
+    /// Returns the size of the texture in pixels.
+    Size<unsigned int> size() const { return inner.size; }
+
+    /// Compares two borrowed OpenGL textures. They are considered equal if all their ids and sizes
+    /// are equal.
+    bool operator==(const BorrowedOpenGLTexture &other) const = default;
+    /// Compares two borrowed OpenGL textures. They are considered equal if any of their ids and
+    /// sizes differ.
+    bool operator!=(const BorrowedOpenGLTexture &other) const = default;
+
+private:
+    cbindgen_private::types::BorrowedOpenGLTexture inner;
+    friend struct Image;
+};
+
 /// An image type that can be displayed by the Image element
 ///
 /// You can construct Image objects from a path to an image file on disk, using
@@ -143,6 +179,12 @@ public:
     {
     }
 
+    /// Construct an image from a borrowed OpenGL texture.
+    Image(BorrowedOpenGLTexture texture)
+        : data(Data::ImageInner_BorrowedOpenGLTexture(texture.inner))
+    {
+    }
+
     /// Returns the size of the Image in pixels.
     Size<unsigned int> size() const { return cbindgen_private::types::slint_image_size(&data); }