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/app/commands/pdf_dialogs.rs

@@ -582,6 +582,8 @@ impl OpenCADStudio {
             | PdfDialogMsg::BgBrowse
             | PdfDialogMsg::BgPosition(_)
             | PdfDialogMsg::BgAspect(_)
+            | PdfDialogMsg::BgOffset(_)
+            | PdfDialogMsg::BgScale(_)
             | PdfDialogMsg::BgApply) => return self.update_view_background(message),
             message @ (PdfDialogMsg::SecPerimeter(_)
             | PdfDialogMsg::SecMaxPoints(_)

src/app/commands/view_presets.rs

@@ -507,6 +507,8 @@ impl OpenCADStudio {
             M::BgImage(value) => state.image = value,
             M::BgPosition(value) => state.position = value,
             M::BgAspect(on) => state.aspect = on,
+            M::BgOffset(value) => state.offset = value,
+            M::BgScale(value) => state.scale = value,
             M::BgColor(slot, rgb) => match slot {
                 0 => state.solid = rgb,
                 1 => state.top = rgb,

src/app/control/actions.rs

@@ -1798,7 +1798,7 @@ impl OpenCADStudio {
             "ribbon_dropdown" => Message::ToggleRibbonDropdown(string(req, "value")?.into()),
             // The -VIEW Background dialog, one field per call: "type=gradient",
             // "color|top|middle|bottom=r,g,b", "three=1", "rotation=30",
-            // "image=<path>", "position=center|stretch|tile", "aspect=1",
+            // "image=<path>", "position=center|stretch|tile", "aspect=1", "offset=x,y" (pixels), "scale=x,y" (non-zero),
             // "apply" or "cancel".
             "view_background" => {
                 use crate::ui::window::pdf_dialogs::{BgKind, BgPosition, PdfDialogMsg as P};
@@ -1840,6 +1840,21 @@ impl OpenCADStudio {
                         _ => return Err(bad()),
                     })),
                     "aspect" => Message::PdfDialog(P::BgAspect(value == "1")),
+                    "offset" | "scale" => {
+                        let pair: Vec<f64> = value
+                            .split(',')
+                            .map(|part| part.trim().parse::<f64>())
+                            .collect::<Result<_, _>>()
+                            .map_err(|_| bad())?;
+                        let pair = <[f64; 2]>::try_from(pair).map_err(|_| bad())?;
+                        if key == "offset" {
+                            Message::PdfDialog(P::BgOffset(pair))
+                        } else if pair.iter().all(|v| v.is_finite() && *v != 0.0) {
+                            Message::PdfDialog(P::BgScale(pair))
+                        } else {
+                            return Err(bad());
+                        }
+                    }
                     _ => return Err(bad()),
                 }
             }

src/app/update/viewport.rs

@@ -1084,6 +1084,9 @@ impl OpenCADStudio {
         // viewport, the picker drives that viewport entity's own
         // render mode; the model-layout tab style is untouched.
         if self.tabs[i].scene.set_active_viewport_render_mode(mode) {
+            self.tabs[i]
+                .scene
+                .set_active_visual_style_named(crate::modules::view::visual_style::style_name_for(mode));
             self.tabs[i].scene.bump_geometry_no_blocks();
             self.tabs[i].dirty = true;
             self.command_line

src/app/view/mod.rs

@@ -182,6 +182,24 @@ impl std::fmt::Display for RenderModeChoice {
     }
 }
 
+/// A named style (Realistic, …) the active viewport draws as, by name.
+fn named_visual_style(
+    scene: &crate::scene::Scene,
+    mode: codec::entities::ViewportRenderMode,
+) -> Option<String> {
+    match scene.document.objects.get(&scene.active_visual_style()) {
+        Some(codec::objects::ObjectType::VisualStyle(style)) => {
+            match crate::modules::view::visual_style::mode_for_style_name(&style.description) {
+                Some((named_mode, true)) if named_mode == mode => {
+                    Some(crate::t!(style.description.as_str()).into_owned())
+                }
+                _ => None,
+            }
+        }
+        _ => None,
+    }
+}
+
 impl OpenCADStudio {
     #[cfg(not(target_arch = "wasm32"))]
     pub fn view(&self, window_id: window::Id) -> Element<'_, Message> {
@@ -1297,18 +1315,7 @@ bg={bg_ms:.1}ms n={view_count}"
                 let rect = tab.scene.active_model_tile_bounds(vw, vh);
                 // Unified control chip: split buttons + render-mode picker +
                 // grid / grid-snap toggles, for the active Model tile.
-                // A named style (Realistic, …) the tile draws as shows by name.
-                let style_name = match tab.scene.document.objects.get(&tab.scene.active_visual_style()) {
-                    Some(codec::objects::ObjectType::VisualStyle(style)) => {
-                        match crate::modules::view::visual_style::mode_for_style_name(&style.description) {
-                            Some((mode, true)) if mode == tab.render_mode => {
-                                Some(crate::t!(style.description.as_str()).into_owned())
-                            }
-                            _ => None,
-                        }
-                    }
-                    _ => None,
-                };
+                let style_name = named_visual_style(&tab.scene, tab.render_mode);
                 let bar = viewport_controls(
                     tab.render_mode,
                     self.show_grid,
@@ -1410,7 +1417,7 @@ bg={bg_ms:.1}ms n={view_count}"
                     0,
                     self.render_mode_menu_open,
                     self.render_mode_preview,
-                    None,
+                    named_visual_style(&tab.scene, vp_mode),
                 );
                 let adaptive: Element<'_, Message> = DensitySwap::new(vec![
                     iced::widget::opaque(bar),