Actually remove the GraphicsBackend completely

It is not longer in used for the abstraction between backend,
we'll make a new trait for it later

sixtyfps_runtime/corelib/graphics.rs

@@ -11,10 +11,7 @@ LICENSE END */
 /*!
     Graphics Abstractions.
 
-    This module contains the abstractions and convenience types to allow the runtime
+    This module contains the abstractions and convenience types used for rendering.
-    library to instruct different graphics backends to render the tree of items.
-
-    The entry trait is [GraphicsBackend].
 
     The run-time library also makes use of [RenderingCache] to store the rendering primitives
     created by the backend in a type-erased manner.
@@ -305,25 +302,6 @@ pub trait FontMetrics {
     fn height(&self) -> f32;
 }
 
-/// GraphicsBackend is the trait that the the SixtyFPS run-time uses to convert [HighLevelRenderingPrimitive]
-/// to an internal representation that is optimal for the backend, in order to render it later. The internal
-/// representation is opaque but must be provided via the [GraphicsBackend::LowLevelRenderingPrimitive] associated type.
-///
-/// The backend operates in two modes:
-///   1. It can be used to create new rendering primitives, by calling [GraphicsBackend::new_rendering_primitives_builder]. This is
-///      usually an expensive step, that involves uploading data to the GPU or performing other pre-calculations.
-///
-///   1. A series of low-level rendering primitives can be rendered into a frame, that's started using [GraphicsBackend::new_frame].
-///      The low-level rendering primitives are intended to be fast and ready for rendering.
-pub trait GraphicsBackend: Sized {
-    /// Returns a FontMetrics trait object that can be used to measure text and that matches the given font request as
-    /// closely as possible.
-    fn font_metrics(&mut self, request: FontRequest) -> Box<dyn FontMetrics>;
-
-    /// Returns the window that the backend is associated with.
-    fn window(&self) -> &winit::window::Window;
-}
-
 #[repr(C)]
 #[derive(FieldOffsets, Default, SixtyFPSElement, Clone, Debug, PartialEq)]
 #[pin]

sixtyfps_runtime/rendering_backends/gl/graphics_window.rs

@@ -8,7 +8,6 @@
     Please contact info@sixtyfps.io for more information.
 LICENSE END */
 //! This module contains the GraphicsWindow that used to be within corelib.
-//! FIXME The GraphicsWindow probably does not need to be generic
 
 use core::cell::{Cell, RefCell};
 use core::pin::Pin;
@@ -25,6 +24,7 @@ use corelib::window::{ComponentWindow, GenericWindow};
 use corelib::Property;
 use sixtyfps_corelib as corelib;
 
+/// FIXME! this is some remains from a time where the GLRenderer was called the backend
 type Backend = super::GLRenderer;
 
 type WindowFactoryFn =

sixtyfps_runtime/rendering_backends/gl/lib.rs

@@ -15,7 +15,7 @@ use std::{
 };
 
 use sixtyfps_corelib::graphics::{
-    Color, FontMetrics, FontRequest, GraphicsBackend, Point, Rect, RenderingCache, Resource,
+    Color, FontMetrics, FontRequest, Point, Rect, RenderingCache, Resource,
 };
 use sixtyfps_corelib::item_rendering::{CachedRenderingData, ItemRenderer};
 use sixtyfps_corelib::items::ImageFit;
@@ -270,9 +270,9 @@ impl GLRenderer {
             loaded_fonts: Default::default(),
         }
     }
-}
 
-impl GLRenderer {
+    /// Returns a new item renderer instance. At this point rendering begins and the backend ensures that the
+    /// window background was cleared with the specified clear_color.
     fn new_renderer(&mut self, clear_color: &Color) -> GLItemRenderer {
         let (size, scale_factor) = {
             let window = self.window();
@@ -307,6 +307,8 @@ impl GLRenderer {
         }
     }
 
+    /// Complete the item rendering by calling this function. This will typically flush any remaining/pending
+    /// commands to the underlying graphics subsystem.
     fn flush_renderer(&mut self, _renderer: GLItemRenderer) {
         self.canvas.borrow_mut().flush();
 
@@ -324,9 +326,7 @@ impl GLRenderer {
                 .map_or(false, |cached_image_rc| Rc::strong_count(&cached_image_rc) > 1)
         });
     }
-}
 
-impl GraphicsBackend for GLRenderer {
     fn window(&self) -> &winit::window::Window {
         #[cfg(not(target_arch = "wasm32"))]
         return self.windowed_context.as_ref().unwrap().window();
@@ -334,6 +334,8 @@ impl GraphicsBackend for GLRenderer {
         return &self.window;
     }
 
+    /// Returns a FontMetrics trait object that can be used to measure text and that matches the given font request as
+    /// closely as possible.
     fn font_metrics(&mut self, request: FontRequest) -> Box<dyn FontMetrics> {
         Box::new(GLFontMetrics {
             request,