winit: Always make skia-opengl available

The Skia OpenGL renderer is portable and sometimes esp. on Windows produces better results, so make it always available as an open if `renderer-skia` is enabled. `renderer-skia-opengl` continues to select the GL renderer as default.

docs/reference/src/advanced/backend_winit.md

@@ -15,6 +15,7 @@ The Winit backend supports different renderers. They can be explicitly selected
 | FemtoVG       | OpenGL                                      | `winit-femtovg`                          |
 | Skia          | OpenGL, Metal, Direct3D, Software-rendering | `winit-skia`                             |
 | Skia Software | Software-only rendering with Skia           | `winit-skia-software`                    |
+| Skia OpenGL   | OpenGL rendering with Skia                  | `winit-skia-opengl`                      |
 | software      | Software-rendering, no GPU required         | `winit-software`                         |
 
 

internal/backends/winit/lib.rs

@@ -177,6 +177,8 @@ impl Backend {
             Some("gl") | Some("femtovg") => renderer::femtovg::GlutinFemtoVGRenderer::new,
             #[cfg(enable_skia_renderer)]
             Some("skia") => renderer::skia::WinitSkiaRenderer::new,
+            #[cfg(enable_skia_renderer)]
+            Some("skia-opengl") => renderer::skia::WinitSkiaRenderer::new_opengl,
             #[cfg(all(enable_skia_renderer, not(target_os = "android")))]
             Some("skia-software") => renderer::skia::WinitSkiaRenderer::new_software,
             #[cfg(feature = "renderer-software")]

internal/backends/winit/renderer/skia.rs

@@ -58,6 +58,29 @@ impl WinitSkiaRenderer {
 
         Ok((Box::new(Self { renderer }), winit_window))
     }
+
+    pub fn new_opengl(
+        window_builder: winit::window::WindowBuilder,
+    ) -> Result<(Box<dyn super::WinitCompatibleRenderer>, Rc<winit::window::Window>), PlatformError>
+    {
+        let winit_window = Rc::new(crate::event_loop::with_window_target(|event_loop| {
+            window_builder.build(event_loop.event_loop_target()).map_err(|winit_os_error| {
+                format!("Error creating native window for Skia rendering: {}", winit_os_error)
+                    .into()
+            })
+        })?);
+
+        let renderer = i_slint_renderer_skia::SkiaRenderer::default_opengl();
+
+        renderer.set_pre_present_callback(Some(Box::new({
+            let winit_window = winit_window.clone();
+            move || {
+                winit_window.pre_present_notify();
+            }
+        })));
+
+        Ok((Box::new(Self { renderer }), winit_window))
+    }
 }
 
 impl super::WinitCompatibleRenderer for WinitSkiaRenderer {

internal/renderers/skia/Cargo.toml

@@ -21,7 +21,7 @@ path = "lib.rs"
 [features]
 wayland = ["glutin/wayland", "softbuffer/wayland", "softbuffer/wayland-dlopen"]
 x11 = ["glutin/x11", "glutin/glx", "softbuffer/x11", "softbuffer/x11-dlopen"]
-opengl = ["skia-safe/gl"]
+opengl = []
 vulkan = ["skia-safe/vulkan", "ash", "vulkano"]
 kms = ["softbuffer/kms"]
 default = []
@@ -42,7 +42,7 @@ pin-weak = "1"
 scoped-tls-hkt = "0.1"
 raw-window-handle = { version = "0.5", features = ["std"] }
 
-skia-safe = { version = "0.69.0", features = ["textlayout"] }
+skia-safe = { version = "0.69.0", features = ["textlayout", "gl"] }
 glow = { version = "0.13" }
 unicode-segmentation = { version = "1.8.0" }
 

internal/renderers/skia/lib.rs

@@ -43,7 +43,6 @@ pub mod d3d_surface;
 #[cfg(skia_backend_vulkan)]
 pub mod vulkan_surface;
 
-#[cfg(skia_backend_opengl)]
 pub mod opengl_surface;
 
 pub use skia_safe;
@@ -135,6 +134,24 @@ impl SkiaRenderer {
         }
     }
 
+    /// Creates a new SkiaRenderer that will always use Skia's OpenGL renderer.
+    pub fn default_opengl() -> Self {
+        Self {
+            maybe_window_adapter: Default::default(),
+            rendering_notifier: Default::default(),
+            image_cache: Default::default(),
+            path_cache: Default::default(),
+            rendering_metrics_collector: Default::default(),
+            rendering_first_time: Default::default(),
+            surface: Default::default(),
+            surface_factory: |window_handle, display_handle, size| {
+                opengl_surface::OpenGLSurface::new(window_handle, display_handle, size)
+                    .map(|r| Box::new(r) as Box<dyn Surface>)
+            },
+            pre_present_callback: Default::default(),
+        }
+    }
+
     /// Creates a new renderer is associated with the provided window adapter.
     pub fn new(
         window_handle: raw_window_handle::WindowHandle<'_>,