Set up the cross-fade animation

cyberpunk-slideshow/script.yml

@@ -1,18 +1,18 @@
 - text: The distinguishing thing about magic is that it includes some kind of personal element. The person who is performing the magic is relevant to the magic. -- Ted Chang, Marie Brennan
   position: top
   transition:
-    secs: 2
+    secs: 1
     nanos: 0
 
 - text: Any sufficiently advanced technology is indistinguishable from magic. -- Arthur C. Clark.
   position: middle
   transition:
-    secs: 2
+    secs: 1
     nanos: 0
 
-- text: Electricity is the closest we get to Magic in this world.
+- text: Science is our Magic.
   position: middle
   transition:
-    secs: 2
+    secs: 1
     nanos: 0
 

cyberpunk-slideshow/src/main.rs

@@ -1,5 +1,6 @@
 use std::{
     cell::RefCell,
+    collections::HashMap,
     fs::File,
     io::Read,
     ops::Index,
@@ -22,7 +23,7 @@ use serde::{Deserialize, Serialize};
 const FPS: u64 = 60;
 const PURPLE: (f64, f64, f64) = (0.7, 0., 1.);
 
-#[derive(Serialize, Deserialize, Debug, Clone)]
+#[derive(Serialize, Deserialize, Debug, Clone, PartialEq, Eq, Hash)]
 #[serde(rename_all = "lowercase")]
 enum Position {
     Top,
@@ -72,6 +73,13 @@ impl Index<usize> for Script {
     }
 }
 
+struct Region {
+    left: f64,
+    top: f64,
+    width: f64,
+    height: f64,
+}
+
 struct Fade {
     text: String,
     position: Position,
@@ -80,29 +88,10 @@ struct Fade {
     start_time: Instant,
 }
 
-/*
-impl Fade {
-    fn render(&self, context: &Context) {
-        let start = Instant::now();
-    }
-}
-*/
-
-/*
-impl Transition {
-    fn render(&self, context: &Context) {
-        match self {
-            Transition::Fade(fade) => fade.render(context),
-            Transition::CrossFade(start, end) => {}
-        }
-    }
-}
-*/
-
 trait Animation {
     fn position(&self) -> Position;
 
-    fn tick(&self, now: Instant, context: &Context) -> bool;
+    fn tick(&self, now: Instant, context: &Context, region: Region);
 }
 
 impl Animation for Fade {
@@ -110,18 +99,50 @@ impl Animation for Fade {
         self.position.clone()
     }
 
-    fn tick(&self, now: Instant, context: &Context) -> bool {
+    fn tick(&self, now: Instant, context: &Context, region: Region) {
         let total_frames = self.duration.as_secs() * FPS;
         let alpha_rate: f64 = 1. / total_frames as f64;
 
         let frames = (now - self.start_time).as_secs_f64() * FPS as f64;
         let alpha = alpha_rate * frames as f64;
 
-        let _ = context.set_source_rgba(PURPLE.0, PURPLE.1, PURPLE.2, alpha);
         let text_display = Text::new(self.text.clone(), context, 32.);
+        let _ = context.move_to(region.left, region.top + text_display.extents().height());
+        let _ = context.set_source_rgba(PURPLE.0, PURPLE.1, PURPLE.2, alpha);
+        text_display.draw();
+    }
+}
+
+struct CrossFade {
+    old_text: String,
+    new_text: String,
+    position: Position,
+    duration: Duration,
+
+    start_time: Instant,
+}
+
+impl Animation for CrossFade {
+    fn position(&self) -> Position {
+        self.position.clone()
+    }
+
+    fn tick(&self, now: Instant, context: &Context, region: Region) {
+        let total_frames = self.duration.as_secs() * FPS;
+        let alpha_rate: f64 = 1. / total_frames as f64;
+
+        let frames = (now - self.start_time).as_secs_f64() * FPS as f64;
+        let alpha = alpha_rate * frames as f64;
+
+        let text_display = Text::new(self.old_text.clone(), context, 32.);
+        let _ = context.move_to(region.left, region.top + text_display.extents().height());
+        let _ = context.set_source_rgba(PURPLE.0, PURPLE.1, PURPLE.2, 1. - alpha);
         text_display.draw();
 
-        false
+        let text_display = Text::new(self.new_text.clone(), context, 32.);
+        let _ = context.move_to(region.left, region.top + text_display.extents().height());
+        let _ = context.set_source_rgba(PURPLE.0, PURPLE.1, PURPLE.2, alpha);
+        text_display.draw();
     }
 }
 
@@ -153,7 +174,7 @@ impl CyberScreenState {
         s
     }
 
-    fn next_page(&mut self) -> impl Animation {
+    fn next_page(&mut self) -> Box<dyn Animation> {
         let idx = match self.idx {
             None => 0,
             Some(idx) => {
@@ -167,22 +188,35 @@ impl CyberScreenState {
         self.idx = Some(idx);
         let step = self.script[idx].clone();
 
-        match step.position {
+        let (old, new) = match step.position {
             Position::Top => {
-                self.top = Some(step.clone());
+                let old = self.top.replace(step.clone());
+                (old, step)
             }
             Position::Middle => {
-                self.middle = Some(step.clone());
+                let old = self.middle.replace(step.clone());
+                (old, step)
             }
             Position::Bottom => {
-                self.bottom = Some(step.clone());
+                let old = self.middle.replace(step.clone());
+                (old, step)
             }
-        }
+        };
-        Fade {
+
-            text: step.text.clone(),
+        match old {
-            position: step.position,
+            Some(old) => Box::new(CrossFade {
-            duration: step.transition,
+                old_text: old.text.clone(),
+                new_text: new.text.clone(),
+                position: new.position,
+                duration: new.transition,
                 start_time: Instant::now(),
+            }),
+            None => Box::new(Fade {
+                text: new.text.clone(),
+                position: new.position,
+                duration: new.transition,
+                start_time: Instant::now(),
+            }),
         }
     }
 }
@@ -190,7 +224,9 @@ impl CyberScreenState {
 #[derive(Default)]
 pub struct CyberScreenPrivate {
     state: Rc<RefCell<CyberScreenState>>,
-    animations: Rc<RefCell<Vec<Box<dyn Animation>>>>,
+    // For crossfading to work, I have to detect that there is an old animation in a position, and
+    // replace it with the new one.
+    animations: Rc<RefCell<HashMap<Position, Box<dyn Animation>>>>,
 }
 
 #[glib::object_subclass]
@@ -211,7 +247,9 @@ impl CyberScreenPrivate {
 
     fn next_page(&self) {
         let transition = self.state.borrow_mut().next_page();
-        self.animations.borrow_mut().push(Box::new(transition));
+        self.animations
+            .borrow_mut()
+            .insert(transition.position(), transition);
     }
 }
 
@@ -239,27 +277,56 @@ impl CyberScreen {
                 }
                 pen.stroke();
                 */
+                let line = AsymLineCutout {
+                    orientation: gtk::Orientation::Horizontal,
+                    start_x: 25.,
+                    start_y: height as f64 / 7.,
+                    start_length: width as f64 / 3.,
+                    cutout_length: width as f64 / 3. - 25.,
+                    height: 25.,
+                    end_length: width as f64 / 3. - 50.,
+                    invert: false,
+                }.draw(&pen);
+                pen.stroke();
                 let tracery = pen.finish();
                 let _ = context.set_source(tracery);
                 let _ = context.paint();
 
                 let mut animations = s.imp().animations.borrow_mut();
-                let mut to_remove = vec![];
-                for (idx, animation) in animations.iter().enumerate() {
-                    let y = match animation.position() {
-                        Position::Top => height as f64 * 1. / 5.,
-                        Position::Middle => height as f64 * 2. / 5.,
-                        Position::Bottom => height as f64 * 3. / 5.,
-                    };
-                    context.move_to(20., y);
-                    let done = animation.tick(now, context);
-                    if done {
-                        to_remove.push(idx)
-                    };
-                }
 
-                for idx in to_remove.into_iter() {
+                let lr_margin = 50.;
-                    animations.remove(idx);
+                let max_width = width as f64 - lr_margin * 2.;
+                let region_height = height as f64 / 5.;
+
+                if let Some(animation) = animations.get(&Position::Top) {
+                    let y = height as f64 * 1. / 5.;
+                    let region = Region {
+                        left: 20.,
+                        top: y,
+                        height: region_height,
+                        width: max_width,
+                    };
+                    animation.tick(now, context, region);
+                }
+                if let Some(animation) = animations.get(&Position::Middle) {
+                    let y = height as f64 * 2. / 5.;
+                    let region = Region {
+                        left: 20.,
+                        top: y,
+                        height: region_height,
+                        width: max_width,
+                    };
+                    animation.tick(now, context, region);
+                }
+                if let Some(animation) = animations.get(&Position::Bottom) {
+                    let y = height as f64 * 3. / 5.;
+                    let region = Region {
+                        left: 20.,
+                        top: y,
+                        height: region_height,
+                        width: max_width,
+                    };
+                    animation.tick(now, context, region);
                 }
             }
         });
@@ -316,10 +383,12 @@ fn main() {
 
         let _ = glib::spawn_future_local({
             let screen = screen.clone();
-            async move { loop {
+            async move {
+                loop {
                     screen.queue_draw();
                     async_std::task::sleep(Duration::from_millis(1000 / FPS)).await;
-            }}
+                }
+            }
         });
     });