Raster images: transparency off draws pixels opaque; TRANSPARENCY command

An image's transparency flag decides whether transparent pixels show what
is behind the image or draw in their stored colour: the image pass and PDF
plots now follow it (it was ignored, so every PNG alpha showed through).
TRANSPARENCY selects images and asks for the mode, defaulting to the first
image's current one.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

src/modules/insert/image_transparency.rs

@@ -0,0 +1,93 @@
+// TRANSPARENCY — whether raster images show their transparent pixels as
+// transparent or draw every pixel in its stored colour.
+//
+//   Select image(s):
+//   Enter transparency mode [ON/OFF] <OFF>:     (the default is the first
+//                                                image's current mode)
+
+use codec::Handle;
+use glam::DVec3;
+
+use crate::command::{CadCommand, CmdOption, CmdResult};
+
+pub struct TransparencyCommand {
+    handles: Vec<Handle>,
+    /// `None` while images are being selected; then the default mode.
+    default_on: Option<bool>,
+}
+
+impl TransparencyCommand {
+    pub fn new() -> Self {
+        Self { handles: Vec::new(), default_on: None }
+    }
+
+    /// The mode prompt for images already chosen.
+    pub fn mode(handles: Vec<Handle>, default_on: bool) -> Self {
+        Self { handles, default_on: Some(default_on) }
+    }
+
+    fn apply(&mut self, on: bool) -> CmdResult {
+        let command = if on { "TRANSPARENCY ON" } else { "TRANSPARENCY OFF" };
+        CmdResult::Relaunch(command.to_string(), std::mem::take(&mut self.handles))
+    }
+}
+
+impl CadCommand for TransparencyCommand {
+    fn name(&self) -> &'static str {
+        "TRANSPARENCY"
+    }
+
+    fn prompt(&self) -> String {
+        match self.default_on {
+            None => crate::t!("Select image(s):").into_owned(),
+            Some(true) => crate::t!("Enter transparency mode [ON/OFF] <ON>:").into_owned(),
+            Some(false) => crate::t!("Enter transparency mode [ON/OFF] <OFF>:").into_owned(),
+        }
+    }
+
+    fn options(&self) -> Vec<CmdOption> {
+        match self.default_on {
+            None => Vec::new(),
+            Some(_) => vec![CmdOption::new("ON", "ON"), CmdOption::new("OFF", "OFF")],
+        }
+    }
+
+    fn is_selection_gathering(&self) -> bool {
+        self.default_on.is_none()
+    }
+
+    fn wants_text_input(&self) -> bool {
+        self.default_on.is_some()
+    }
+
+    fn on_selection_complete(&mut self, handles: Vec<Handle>) -> CmdResult {
+        self.handles = handles;
+        CmdResult::NeedPoint
+    }
+
+    fn on_text_input(&mut self, text: &str) -> Option<CmdResult> {
+        let default_on = self.default_on?;
+        Some(match text.trim().to_uppercase().as_str() {
+            "" => self.apply(default_on),
+            "ON" => self.apply(true),
+            "OFF" => self.apply(false),
+            _ => CmdResult::ReportError("Invalid option keyword.".to_string()),
+        })
+    }
+
+    fn on_point(&mut self, _pt: DVec3) -> CmdResult {
+        CmdResult::NeedPoint
+    }
+
+    fn on_enter(&mut self) -> CmdResult {
+        match self.default_on {
+            None if self.handles.is_empty() => CmdResult::Cancel,
+            // The app keeps only the images and asks for the mode.
+            None => CmdResult::Relaunch(
+                "TRANSPARENCY MODE".to_string(),
+                std::mem::take(&mut self.handles),
+            ),
+            Some(on) => self.apply(on),
+        }
+    }
+}

src/modules/insert/mod.rs

@@ -9,6 +9,7 @@ mod content_browser;
 pub(crate) mod create_block;
 mod design_center;
 mod edit_block;
+pub(crate) mod image_transparency;
 pub(crate) mod insert_block;
 mod landxml;
 pub(crate) mod picker;