windows: some minor performance improvements

* Make window invalidation more efficient by avoiding spawning a call
  that spawns a call to invalidate the window.  Just directly mark as
  invalidated.

* Suppress default background erase

* hoist the bg_color calc for quads that don't have Cells outside of
  its loop.

refs: https://github.com/wez/wezterm/issues/546

wezterm-gui/src/shapecache.rs

@@ -194,7 +194,7 @@ where
 /// It's a bit involved to make this work; more details can be
 /// found in the excellent guide here:
 /// <https://github.com/sunshowers/borrow-complex-key-example/blob/master/src/lib.rs>
-#[derive(Copy, Clone, PartialEq, Eq, Hash)]
+#[derive(Copy, Debug, Clone, PartialEq, Eq, Hash)]
 pub struct BorrowedShapeCacheKey<'a> {
     pub style: &'a TextStyle,
     pub text: &'a str,

wezterm-gui/src/termwindow/render.rs

@@ -70,7 +70,7 @@ impl super::TermWindow {
         *self.has_animation.borrow_mut() = None;
 
         self.check_for_config_reload();
-        let start = std::time::Instant::now();
+        let start = Instant::now();
 
         {
             let background_alpha = (self.config.window_background_opacity * 255.0) as u8;
@@ -93,6 +93,7 @@ impl super::TermWindow {
                         let result = if pass == 0 {
                             // Let's try clearing out the atlas and trying again
                             // self.clear_texture_atlas()
+                            log::trace!("recreate_texture_atlas");
                             self.recreate_texture_atlas(Some(current_size))
                         } else {
                             log::trace!("grow texture atlas to {}", size);
@@ -114,9 +115,10 @@ impl super::TermWindow {
                 }
             }
         }
+        log::debug!("paint_impl before call_draw elapsed={:?}", start.elapsed());
 
         self.call_draw(frame).ok();
-        log::debug!("paint_pane_opengl elapsed={:?}", start.elapsed());
+        log::debug!("paint_impl elapsed={:?}", start.elapsed());
         metrics::histogram!("gui.paint.opengl", start.elapsed());
         self.update_title_post_status();
     }
@@ -885,6 +887,15 @@ impl super::TermWindow {
         // the right pane with its prior contents instead of showing the
         // cleared lines from the shell in the main screen.
 
+        let bg_color = rgbcolor_alpha_to_window_color(
+            params.palette.resolve_bg(ColorAttribute::Default),
+            if window_is_transparent {
+                0x00
+            } else {
+                (params.config.text_background_opacity * 255.0) as u8
+            },
+        );
+
         for cell_idx in last_cell_idx.unwrap_or(0) + 1..num_cols {
             // Even though we don't have a cell for these, they still
             // hold the cursor or the selection so we need to compute
@@ -900,14 +911,7 @@ impl super::TermWindow {
                 cursor: params.cursor,
                 selection: &params.selection,
                 fg_color: params.foreground,
-                bg_color: rgbcolor_alpha_to_window_color(
-                    params.palette.resolve_bg(ColorAttribute::Default),
-                    if window_is_transparent {
-                        0x00
-                    } else {
-                        (params.config.text_background_opacity * 255.0) as u8
-                    },
-                ),
+                bg_color,
                 palette: params.palette,
                 is_active_pane: params.pos.is_active,
                 config: params.config,
@@ -1177,6 +1181,7 @@ impl super::TermWindow {
     }
 
     pub fn clear_texture_atlas(&mut self) -> anyhow::Result<()> {
+        log::trace!("clear_texture_atlas");
         self.shape_cache.borrow_mut().clear();
         if let Some(render_state) = self.render_state.as_mut() {
             render_state.clear_texture_atlas(&self.render_metrics)?;

window/src/os/windows/window.rs

@@ -457,8 +457,9 @@ impl WindowOpsMut for WindowInner {
     }
 
     fn invalidate(&mut self) {
+        log::trace!("WindowOpsMut::invalidate");
         unsafe {
-            InvalidateRect(self.hwnd.0, null(), 1);
+            InvalidateRect(self.hwnd.0, null(), 0);
         }
     }
 
@@ -609,10 +610,12 @@ impl WindowOps for Window {
     }
 
     fn invalidate(&self) -> Future<()> {
-        Connection::with_window_inner(self.0, |inner| {
-            inner.invalidate();
-            Ok(())
-        })
+        let hwnd = self.0 .0;
+        log::trace!("WindowOps::invalidate calling InvalidateRect");
+        unsafe {
+            InvalidateRect(hwnd, null(), 0);
+        }
+        Future::ok(())
     }
 
     fn set_title(&self, title: &str) -> Future<()> {
@@ -1909,6 +1912,7 @@ unsafe fn do_wnd_proc(hwnd: HWND, msg: UINT, wparam: WPARAM, lparam: LPARAM) ->
         | WM_RBUTTONDOWN | WM_RBUTTONUP | WM_MBUTTONDOWN | WM_MBUTTONUP => {
             mouse_button(hwnd, msg, wparam, lparam)
         }
+        WM_ERASEBKGND => Some(1),
         WM_CLOSE => {
             if let Some(inner) = rc_from_hwnd(hwnd) {
                 let inner = inner.borrow();