View backgrounds: image colours as stored, viewport style name, adjust automation

- The background image texture is not an sRGB view: the image is drawn with
  its own colours, as the solid and gradient colours are.
- An entered paper-space viewport shows its named visual style (Realistic,
  ...) in the render-mode picker, and a mode picked there is recorded as the
  viewport's visual style.
- The view_background automation action takes offset=x,y and scale=x,y.

Co-Authored-By: Claude Opus 5.5 <[email protected]>

src/scene/camera_ops.rs

@@ -336,6 +336,12 @@ impl Scene {
 
     /// The visual style of the active Model tile's viewport record.
     pub fn active_visual_style(&self) -> Handle {
+        if self.current_layout != "Model" {
+            return match self.active_viewport.and_then(|handle| self.document.get_entity(handle)) {
+                Some(EntityType::Viewport(value)) => value.visual_style_handle,
+                _ => Handle::NULL,
+            };
+        }
         self.active_tile_vport_handle()
             .and_then(|handle| self.document.vports.iter().find(|value| value.handle == handle))
             .map_or(Handle::NULL, |value| value.visual_style_handle)
@@ -348,7 +354,16 @@ impl Scene {
             codec::objects::ObjectType::VisualStyle(style) if style.description == name => Some(*handle),
             _ => None,
         });
-        let (Some(style), Some(handle)) = (style, self.active_tile_vport_handle()) else { return };
+        let Some(style) = style else { return };
+        if self.current_layout != "Model" {
+            if let Some(handle) = self.active_viewport {
+                if let Some(EntityType::Viewport(value)) = self.document.get_entity_mut(handle) {
+                    value.visual_style_handle = style;
+                }
+            }
+            return;
+        }
+        let Some(handle) = self.active_tile_vport_handle() else { return };
         if let Some(value) = self.document.vports.iter_mut().find(|value| value.handle == handle) {
             value.visual_style_handle = style;
         }

src/scene/pipeline/mod.rs

@@ -3996,7 +3996,8 @@ analytic={:.1} regular={:.1} blocks={:.1}",
         }
         let upload = |label: &'static str,
                       image: Option<&crate::scene::model::image_model::DecodedImage>,
-                      fallback: [u8; 4]| {
+                      fallback: [u8; 4],
+                      format: wgpu::TextureFormat| {
             let (width, height, pixels) = image
                 .map(|image| (image.width, image.height, image.pixels.as_slice()))
                 .unwrap_or((1, 1, fallback.as_slice()));
@@ -4010,7 +4011,7 @@ analytic={:.1} regular={:.1} blocks={:.1}",
                 mip_level_count: 1,
                 sample_count: 1,
                 dimension: wgpu::TextureDimension::D2,
-                format: wgpu::TextureFormat::Rgba8UnormSrgb,
+                format,
                 usage: wgpu::TextureUsages::TEXTURE_BINDING | wgpu::TextureUsages::COPY_DST,
                 view_formats: &[],
             });
@@ -4030,8 +4031,21 @@ analytic={:.1} regular={:.1} blocks={:.1}",
             );
             texture
         };
-        self.background_texture = upload("background.texture", background, [0, 0, 0, 255]);
-        self.environment_texture = upload("environment.texture", environment, [128, 128, 128, 255]);
+        // The background image is drawn as it is, like the solid and gradient
+        // colours (an sRGB view would darken it a second time); the
+        // environment map stays sRGB for lighting.
+        self.background_texture = upload(
+            "background.texture",
+            background,
+            [0, 0, 0, 255],
+            wgpu::TextureFormat::Rgba8Unorm,
+        );
+        self.environment_texture = upload(
+            "environment.texture",
+            environment,
+            [128, 128, 128, 255],
+            wgpu::TextureFormat::Rgba8UnormSrgb,
+        );
         self.rebuild_frame_bind_group(device);
         self.background_source_id = background_id;
         self.environment_source_id = environment_id;