screen: return damaged area

src/draw/screen.rs

@@ -22,5 +22,6 @@ use super::*;
 pub trait Screen: Space<Self::Unit> + Send + Sync + Sized {
     type Unit: Coord;
     /// Render drawable in subarea specified by `area`
-    fn show <'t, T: Draw<Self>> (&mut self, area: XYWH<Self::Unit>, content: T);
+    fn show <'t, T: Draw<Self>> (&mut self, area: XYWH<Self::Unit>, content: T) ->
+        Usually<XYWH<Self::Unit>>;
 }

src/eval.rs

@@ -77,7 +77,7 @@ macro_rules! eval_enum ((
 /// ```
 pub fn eval_view <'a, O: Screen + 'a, S> (
     state: &S, output: &mut O, expr: &'a impl Expression
-) -> Usually<bool> where
+) -> Perhaps<XYWH<O::Unit>> where
     S: Interpret<O, XYWH<O::Unit>>
         + for<'b> Namespace<'b, bool>
         + for<'b> Namespace<'b, O::Unit>
@@ -100,7 +100,7 @@ pub fn eval_view <'a, O: Screen + 'a, S> (
     let arg2  = tail1.head();
 
     // First `frags.next()` calls returns the namespace.
-    match frags.next() {
+    Some(match frags.next() {
 
         Some("when") => when(
             state.namespace(arg0?)?.unwrap(),
@@ -132,26 +132,30 @@ pub fn eval_view <'a, O: Screen + 'a, S> (
         ).draw(output),
 
         Some("exact") => eval_xy!(
-            "exact", expr, head, output, state, frags.next(), arg0, arg1, arg2, wh_exact, w_exact, h_exact
+            "exact", expr, head, output, state, frags.next(),
+            arg0, arg1, arg2, wh_exact, w_exact, h_exact
         ),
+
         Some("min") => eval_xy!(
-            "min",   expr, head, output, state, frags.next(), arg0, arg1, arg2, wh_min,   w_min,   h_min
+            "min", expr, head, output, state, frags.next(),
+            arg0, arg1, arg2, wh_min,   w_min,   h_min
         ),
+
         Some("max") => eval_xy!(
-            "max",   expr, head, output, state, frags.next(), arg0, arg1, arg2, wh_max,   w_max,   h_max
+            "max", expr, head, output, state, frags.next(),
+            arg0, arg1, arg2, wh_max,   w_max,   h_max
         ),
+
         Some("push") => eval_xy!(
-            "push",  expr, head, output, state, frags.next(), arg0, arg1, arg2, xy_push,  x_push,  y_push
+            "push", expr, head, output, state, frags.next(),
+            arg0, arg1, arg2, xy_push,  x_push,  y_push
         ),
 
-        _ => return Ok(false)
+        _ => return Ok(None)
 
-    }?;
+    }).transpose()
-
-    Ok(true)
 }
 
-
 /// Interpret TUI-specific layout operation.
 ///
 /// ```
@@ -174,8 +178,8 @@ pub fn eval_view <'a, O: Screen + 'a, S> (
 /// ```
 pub fn eval_view_tui <'a, S> (
     state: &S, output: &mut Tui, expr: impl Expression + 'a
-) -> Usually<bool> where
+) -> Perhaps<XYWH<u16>> where
-    S: Interpret<Tui, ()>
+    S: Interpret<Tui, XYWH<u16>>
         + for<'b>Namespace<'b, bool>
         + for<'b>Namespace<'b, u16>
         + for<'b>Namespace<'b, Color>
@@ -187,11 +191,13 @@ pub fn eval_view_tui <'a, S> (
     let arg0  = args.head();
     let tail0 = args.tail();
     let arg1  = tail0.head();
-    match frags.next() {
+    Ok(Some(match frags.next() {
 
         Some("text") => {
             if let Some(src) = args?.src()? {
-                output.show(output.xywh(), &src)
+                output.show(output.xywh(), &src)?
+            } else {
+                return Ok(None)
             }
         },
 
@@ -202,7 +208,7 @@ pub fn eval_view_tui <'a, S> (
                 state.interpret(output, &arg1)?;
                 // FIXME?: don't max out the used area?
                 Ok(output.area().into())
-            })))
+            })))?
         },
 
         Some("bg") => {
@@ -212,11 +218,10 @@ pub fn eval_view_tui <'a, S> (
                 state.interpret(output, &arg1)?;
                 // FIXME?: don't max out the used area?
                 Ok(output.area().into())
-            })))
+            })))?
         },
 
-        _ => return Ok(false)
+        _ => return Ok(None)
 
-    };
+    }))
-    Ok(true)
 }

src/term.rs

@@ -194,11 +194,12 @@ impl Screen for Tui {
     /// Render drawable in subarea specified by `area`
     fn show <'t, T: Draw<Self>> (
         &mut self, area: XYWH<u16>, content: T
-    ) {
+    ) -> Usually<XYWH<u16>> {
         let previous_area = self.1;
         self.1 = area;
-        let _result_area = content.draw(self);
+        let result_area = content.draw(self);
         self.1 = previous_area;
+        result_area
     }
 }