Added offscreen rendering support for wgpu & tiny-skia exposed with the window::screenshot command.

wgpu/src/backend.rs

@@ -1,4 +1,3 @@
-use crate::core;
 use crate::core::{Color, Font, Point, Size};
 use crate::graphics::backend;
 use crate::graphics::color;
@@ -6,6 +5,7 @@ use crate::graphics::{Primitive, Transformation, Viewport};
 use crate::quad;
 use crate::text;
 use crate::triangle;
+use crate::{core, offscreen};
 use crate::{Layer, Settings};
 
 #[cfg(feature = "tracing")]
@@ -123,6 +123,65 @@ impl Backend {
         self.image_pipeline.end_frame();
     }
 
+    /// Performs an offscreen render pass. If the `format` selected by WGPU is not
+    /// `wgpu::TextureFormat::Rgba8UnormSrgb`, a conversion compute pipeline will run.
+    ///
+    /// Returns `None` if the `frame` is `Rgba8UnormSrgb`, else returns the newly
+    /// converted texture view in `Rgba8UnormSrgb`.
+    pub fn offscreen<T: AsRef<str>>(
+        &mut self,
+        device: &wgpu::Device,
+        queue: &wgpu::Queue,
+        encoder: &mut wgpu::CommandEncoder,
+        clear_color: Option<Color>,
+        frame: &wgpu::TextureView,
+        format: wgpu::TextureFormat,
+        primitives: &[Primitive],
+        viewport: &Viewport,
+        overlay_text: &[T],
+        texture_extent: wgpu::Extent3d,
+    ) -> Option<wgpu::Texture> {
+        #[cfg(feature = "tracing")]
+        let _ = info_span!("iced_wgpu::offscreen", "DRAW").entered();
+
+        self.present(
+            device,
+            queue,
+            encoder,
+            clear_color,
+            frame,
+            primitives,
+            viewport,
+            overlay_text,
+        );
+
+        if format != wgpu::TextureFormat::Rgba8UnormSrgb {
+            log::info!("Texture format is {format:?}; performing conversion to rgba8..");
+            let pipeline = offscreen::Pipeline::new(device);
+
+            let texture = device.create_texture(&wgpu::TextureDescriptor {
+                label: Some("iced_wgpu.offscreen.conversion.source_texture"),
+                size: texture_extent,
+                mip_level_count: 1,
+                sample_count: 1,
+                dimension: wgpu::TextureDimension::D2,
+                format: wgpu::TextureFormat::Rgba8Unorm,
+                usage: wgpu::TextureUsages::STORAGE_BINDING
+                    | wgpu::TextureUsages::COPY_SRC,
+                view_formats: &[],
+            });
+
+            let view =
+                texture.create_view(&wgpu::TextureViewDescriptor::default());
+
+            pipeline.convert(device, texture_extent, frame, &view, encoder);
+
+            return Some(texture);
+        }
+
+        None
+    }
+
     fn prepare_text(
         &mut self,
         device: &wgpu::Device,