[fractal] media viewer: Fix image sizing

[Daniel Garcia Moreno <danigm src gnome org>]

commit d6cd7ca15725aa30dd05fdc8964249447315f147
Author: James Westman <james flyingpimonster net>
Date:   Tue Jun 16 14:25:50 2020 -0500

    media viewer: Fix image sizing
    
    Previously, images in the Media Viewer would not be resized dynamically if the
    window was resized. They would stay at the size they got when they were loaded.
    
    Fixed by changing the behavior of the image widget. `fit_to_width` is renamed
    `shrink_to_fit` to better reflect this new behavior. When it is enabled, the
    image widget does not change its size request. Instead, it always resizes the
    image to fit within its allocation, shrinking (but never expanding) it if
    necessary.
    
    Fixes #493.

 fractal-gtk/src/widgets/image.rs        | 64 ++++++++++++++++++++-------------
 fractal-gtk/src/widgets/media_viewer.rs |  4 +--
 2 files changed, 41 insertions(+), 27 deletions(-)
---
diff --git a/fractal-gtk/src/widgets/image.rs b/fractal-gtk/src/widgets/image.rs
index 245115cd..32254294 100644
--- a/fractal-gtk/src/widgets/image.rs
+++ b/fractal-gtk/src/widgets/image.rs
@@ -32,7 +32,7 @@ pub struct Image {
     /// useful to avoid the scale_simple call on every draw
     pub scaled: Arc<Mutex<Option<Pixbuf>>>,
     pub zoom_level: Arc<Mutex<Option<f64>>>,
-    pub fit_to_width: bool,
+    pub shrink_to_fit: bool,
     pub thumb: bool,
     pub circle: bool,
     pub fixed_size: bool,
@@ -82,12 +82,17 @@ impl Image {
             backend: backend.clone(),
             fixed_size: false,
             centered: false,
-            fit_to_width: false,
+            shrink_to_fit: false,
         }
     }
 
-    pub fn fit_to_width(mut self, f: bool) -> Image {
-        self.fit_to_width = f;
+    /// When the image is drawn, shrink it (if necessary) to fit inside the
+    /// allocated space, both width and height. This is used in the Media
+    /// Viewer, for example, to make sure the image fits the screen.
+    /// Contrast with images in the message feed, which fit to the width but
+    /// expand vertically.
+    pub fn shrink_to_fit(mut self, f: bool) -> Image {
+        self.shrink_to_fit = f;
         self
     }
 
@@ -163,7 +168,7 @@ impl Image {
         let is_circle = self.circle.clone();
         let fixed_size = self.fixed_size;
         let centered = self.centered;
-        let fit_to_width = self.fit_to_width;
+        let shrink_to_fit = self.shrink_to_fit;
         da.connect_draw(move |da, g| {
             let widget_w = da.get_allocated_width();
             let widget_h = da.get_allocated_height();
@@ -172,15 +177,10 @@ impl Image {
             let height = widget_h as f64;
 
             let mut rw = widget_w;
-            if let Some(size) = max_size {
-                let w = size.0;
-                rw = i32::min(w, widget_w);
-            }
-
             let mut rh = widget_h;
             if let Some(size) = max_size {
-                let h = size.1;
-                rh = i32::min(h, widget_h);
+                rw = i32::min(size.0, widget_w);
+                rh = i32::min(size.1, widget_h);
             }
 
             let context = da.get_style_context();
@@ -191,24 +191,21 @@ impl Image {
             }
 
             if let Some(ref pb) = *pix.lock().unwrap() {
-                let (mut pw, mut ph) = adjust_to(pb.get_width(), pb.get_height(), rw, rh);
-
-                if let Ok(mut zoom_level_guard) = zoom_level.lock() {
-                    match zoom_level_guard.clone() {
-                        Some(zl) => {
-                            pw = (pb.get_width() as f64 * zl) as i32;
-                            ph = (pb.get_height() as f64 * zl) as i32;
-                        }
-                        None if fit_to_width => {
-                            *zoom_level_guard = Some(pw as f64 / pb.get_width() as f64);
-                        }
-                        _ => {}
+                let (mut pw, mut ph) = match shrink_to_fit {
+                    true => adjust_shrink_to_fit(pb.get_width(), pb.get_height(), rw, rh),
+                    false => adjust_to(pb.get_width(), pb.get_height(), rw, rh),
+                };
+
+                if let Ok(zoom_level_guard) = zoom_level.lock() {
+                    if let Some(zl) = zoom_level_guard.clone() {
+                        pw = (pb.get_width() as f64 * zl) as i32;
+                        ph = (pb.get_height() as f64 * zl) as i32;
                     }
                 }
 
                 if fixed_size {
                     da.set_size_request(pw, ph);
-                } else {
+                } else if !shrink_to_fit {
                     da.set_size_request(1, ph);
                 }
 
@@ -404,3 +401,20 @@ fn adjust_to(w: i32, h: i32, maxw: i32, maxh: i32) -> (i32, i32) {
 
     (pw, ph)
 }
+
+/// Adjust the `w` x `h` to fit in `maxw` x `maxh`, keeping the aspect ratio.
+/// Do not make `w` x `h` bigger, only smaller.
+fn adjust_shrink_to_fit(w: i32, h: i32, maxw: i32, maxh: i32) -> (i32, i32) {
+    let ratio = w as f64 / h as f64;
+    let t_ratio = maxw as f64 / maxh as f64;
+
+    let (nw, nh) = match t_ratio < ratio {
+        true => (maxw, (maxw as f64 * (1.0 / ratio)) as i32),
+        false => ((maxh as f64 * ratio) as i32, maxh),
+    };
+
+    match nw < w {
+        true => (nw, nh),
+        false => (w, h),
+    }
+}
diff --git a/fractal-gtk/src/widgets/media_viewer.rs b/fractal-gtk/src/widgets/media_viewer.rs
index a0f8af7a..af879d8f 100644
--- a/fractal-gtk/src/widgets/media_viewer.rs
+++ b/fractal-gtk/src/widgets/media_viewer.rs
@@ -368,7 +368,7 @@ impl Data {
         match msg.mtype.as_ref() {
             "m.image" => {
                 let image = image::Image::new(&self.backend, self.server_url.clone(), &url)
-                    .fit_to_width(true)
+                    .shrink_to_fit(true)
                     .center(true)
                     .build();
                 media_viewport.add(&image.widget);
@@ -724,7 +724,7 @@ impl MediaViewer {
             "m.image" => {
                 let image =
                     image::Image::new(&self.backend, self.data.borrow().server_url.clone(), &url)
-                        .fit_to_width(true)
+                        .shrink_to_fit(true)
                         .center(true)
                         .build();