From 5b94a0d5a9d108ba45c164ae67b827a819766dba Mon Sep 17 00:00:00 2001
From: Timothy Warren <twarren@nabancard.com>
Date: Mon, 27 Jul 2020 10:52:48 -0400
Subject: [PATCH] Complete 3.4 Batch rendering

---
 Cargo.toml                      |  3 +-
 src/systems/rendering_system.rs | 52 ++++++++++++++++++++++++---------
 2 files changed, 41 insertions(+), 14 deletions(-)

diff --git a/Cargo.toml b/Cargo.toml
index 9fb6709..b192b47 100644
--- a/Cargo.toml
+++ b/Cargo.toml
@@ -8,4 +8,5 @@ edition = "2018"
 
 [dependencies]
 ggez = "0.5.1"
-specs = { version="0.16.1", features=["specs-derive"] }
\ No newline at end of file
+specs = { version="0.16.1", features=["specs-derive"] }
+itertools = "0.9.0"
\ No newline at end of file
diff --git a/src/systems/rendering_system.rs b/src/systems/rendering_system.rs
index f3fba17..d19a34f 100644
--- a/src/systems/rendering_system.rs
+++ b/src/systems/rendering_system.rs
@@ -1,9 +1,12 @@
 use ggez::graphics::Image;
 use ggez::graphics::{Color, DrawParam};
-use ggez::nalgebra as na;
+use ggez::{nalgebra as na, timer};
 use ggez::{graphics, Context};
+use ggez::graphics::spritebatch::SpriteBatch;
+use itertools::Itertools;
 use specs::{Join, Read, ReadStorage, System};
 
+use std::collections::HashMap;
 use std::time::Duration;
 
 use crate::components::*;
@@ -31,7 +34,7 @@ impl RenderingSystem<'_> {
         .expect("expected drawing queued text");
     }
 
-    pub fn get_image(&mut self, renderable: &Renderable, delta: Duration) -> Image {
+    pub fn get_image(&mut self, renderable: &Renderable, delta: Duration) -> String {
         let path_index = match renderable.kind() {
             RenderableKind::Static => {
                 // We only have one image, so we just return that
@@ -47,9 +50,7 @@ impl RenderingSystem<'_> {
             }
         };
 
-        let image_path = renderable.path(path_index);
-
-        Image::new(self.context, image_path).expect("expected image")
+        renderable.path(path_index)
     }
 }
 
@@ -67,27 +68,52 @@ impl<'a> System<'a> for RenderingSystem<'a> {
         // Clear the screen/set the background
         graphics::clear(self.context, graphics::Color::new(0.95, 0.95, 0.95, 1.0));
 
-        // Get all the renderables with their positions and sort by the position z
-        // This will allow us to have entities layered visually.
-        let mut rendering_data = (&positions, &renderables).join().collect::<Vec<_>>();
-        rendering_data.sort_by(|&a, &b| a.0.z.partial_cmp(&b.0.z).expect("expected comparison"));
+        // Get all the renderables with their positions
+        let rendering_data = (&positions, &renderables).join().collect::<Vec<_>>();
+        let mut rendering_batches: HashMap<u8, HashMap<String, Vec<DrawParam>>> = HashMap::new();
 
         // Iterate through all paris of positions & renderables, load the image
         // and draw it at the specified position.
         for (position, renderable) in rendering_data.iter() {
             // Load the image
-            let image = self.get_image(renderable, time.delta);
+            let image_path = self.get_image(renderable, time.delta);
             let x = position.x as f32 * TILE_WIDTH;
             let y = position.y as f32 * TILE_WIDTH;
+            let z = position.z;
 
-            // draw
-            let draw_params = DrawParam::new().dest(na::Point2::new(x, y));
-            graphics::draw(self.context, &image, draw_params).expect("expected render");
+            // Add to rendering batches
+            let draw_param = DrawParam::new().dest(na::Point2::new(x, y));
+            rendering_batches
+                .entry(z)
+                .or_default()
+                .entry(image_path)
+                .or_default()
+                .push(draw_param);
+        }
+
+        // Iterate spritebatches ordered by z and actually render each of them
+        for (_z, group) in rendering_batches
+            .iter()
+            .sorted_by(|a, b| Ord::cmp(&a.0, &b.0)) {
+
+            for (image_path, draw_params) in group {
+                let image = Image::new(self.context, image_path).expect("expected image");
+                let mut sprite_batch = SpriteBatch::new(image);
+
+                for draw_param in draw_params.iter() {
+                    sprite_batch.add(*draw_param);
+                }
+
+                graphics::draw(self.context, &sprite_batch, graphics::DrawParam::new())
+                    .expect("expected render");
+            }
         }
 
         // Render any text
         self.draw_text(&gameplay.state.to_string(), 525.0, 80.0);
         self.draw_text(&gameplay.moves_count.to_string(), 525.0, 100.0);
+        let fps = format!("FPS: {:.0}", timer::fps(self.context));
+        self.draw_text(&fps, 525.0, 120.0);
 
         // Finally, present the context, this will actually display everything
         // on the screen.