From 7ae79fcba5d918dc100e58754683f4433cf7a5b8 Mon Sep 17 00:00:00 2001
From: Victor Brekenfeld <github@drakulix.de>
Date: Wed, 29 Dec 2021 15:55:44 +0100
Subject: [PATCH] winit: Support damage-tracking

---
 src/backend/winit/mod.rs | 72 +++++++++++++++++++++++++++++-----------
 1 file changed, 53 insertions(+), 19 deletions(-)

diff --git a/src/backend/winit/mod.rs b/src/backend/winit/mod.rs
index 63a7a3f..46f5f7b 100644
--- a/src/backend/winit/mod.rs
+++ b/src/backend/winit/mod.rs
@@ -27,11 +27,11 @@ use crate::{
         },
         input::InputEvent,
         renderer::{
-            gles2::{Gles2Error, Gles2Frame, Gles2Renderer},
-            Bind, Renderer, Transform, Unbind,
+            gles2::{Gles2Error, Gles2Renderer},
+            Bind,
         },
     },
-    utils::{Logical, Physical, Size},
+    utils::{Logical, Physical, Rectangle, Size},
 };
 use std::{cell::RefCell, rc::Rc, time::Instant};
 use wayland_egl as wegl;
@@ -90,6 +90,7 @@ pub struct WinitGraphicsBackend {
     egl: Rc<EGLSurface>,
     window: Rc<WinitWindow>,
     size: Rc<RefCell<WindowSize>>,
+    damage_tracking: bool,
     resize_notification: Rc<Cell<Option<Size<i32, Physical>>>>,
 }
 
@@ -220,6 +221,10 @@ where
     let egl = Rc::new(surface);
     let renderer = unsafe { Gles2Renderer::new(context, log.clone())? };
     let resize_notification = Rc::new(Cell::new(None));
+    let damage_tracking = display.extensions.iter().any(|ext| ext == "EGL_EXT_buffer_age")
+        && display.extensions.iter().any(|ext| {
+            ext == "EGL_KHR_swap_buffers_with_damage" || ext == "EGL_EXT_swap_buffers_with_damage"
+        });
 
     Ok((
         WinitGraphicsBackend {
@@ -227,6 +232,7 @@ where
             _display: display,
             egl,
             renderer,
+            damage_tracking,
             size: size.clone(),
             resize_notification: resize_notification.clone(),
         },
@@ -281,28 +287,56 @@ impl WinitGraphicsBackend {
         &mut self.renderer
     }
 
-    /// Shortcut to `Renderer::render` with the current window dimensions
-    /// and this window set as the rendering target.
-    pub fn render<F, R>(&mut self, rendering: F) -> Result<R, crate::backend::SwapBuffersError>
-    where
-        F: FnOnce(&mut Gles2Renderer, &mut Gles2Frame) -> R,
-    {
+    /// Bind the underlying window to the underlying renderer
+    pub fn bind(&mut self) -> Result<(), crate::backend::SwapBuffersError> {
         // Were we told to resize?
         if let Some(size) = self.resize_notification.take() {
             self.egl.resize(size.w, size.h, 0, 0);
         }
 
-        let size = {
-            let size = self.size.borrow();
-            size.physical_size
-        };
-
         self.renderer.bind(self.egl.clone())?;
-        // Why is winit falling out of place with the coordinate system?
-        let result = self.renderer.render(size, Transform::Flipped180, rendering)?;
-        self.egl.swap_buffers()?;
-        self.renderer.unbind()?;
-        Ok(result)
+        Ok(())
+    }
+
+    /// Retrieve the buffer age of the current backbuffer of the window
+    pub fn buffer_age(&self) -> usize {
+        if self.damage_tracking {
+            self.egl.buffer_age() as usize
+        } else {
+            0
+        }
+    }
+
+    /// Submits the back buffer to the window by swapping, requires the window to be previously bound (see [`WinitGraphicsBackend::bind`]).
+    pub fn submit(
+        &mut self,
+        damage: Option<&[Rectangle<i32, Logical>]>,
+        scale: f64,
+    ) -> Result<(), crate::backend::SwapBuffersError> {
+        let mut damage = if self.damage_tracking && damage.is_some() && !damage.unwrap().is_empty() {
+            let size = self
+                .size
+                .borrow()
+                .physical_size
+                .to_f64()
+                .to_logical(scale)
+                .to_i32_round::<i32>();
+            let damage = damage
+                .unwrap()
+                .iter()
+                .map(|rect| {
+                    Rectangle::from_loc_and_size((rect.loc.x, size.h - rect.loc.y - rect.size.h), rect.size)
+                        .to_f64()
+                        .to_physical(scale)
+                        .to_i32_round::<i32>()
+                })
+                .collect::<Vec<_>>();
+            Some(damage)
+        } else {
+            None
+        };
+        self.egl.swap_buffers(damage.as_mut().map(|x| &mut **x))?;
+        Ok(())
     }
 }