From d6d24ba408cef925d30ade479cb93bbc14c4b16b Mon Sep 17 00:00:00 2001
From: Guilherme Werner <guilherme.werner@tribufu.com>
Date: Fri, 16 Feb 2024 20:41:33 -0300
Subject: [PATCH] Index buffer

---
 Cargo.toml |  2 +-
 src/lib.rs | 46 ++++++++++++++++++++++++++++------------------
 2 files changed, 29 insertions(+), 19 deletions(-)

diff --git a/Cargo.toml b/Cargo.toml
index edd2ec0..d18bf8f 100644
--- a/Cargo.toml
+++ b/Cargo.toml
@@ -23,7 +23,7 @@ env_logger = "0.10"
 log = "0.4"
 wgpu = "0.18"
 winit = "0.28"
-bytemuck = { version = "1.12", features = [ "derive" ] }
+bytemuck = { version = "1.12", features = ["derive"] }
 
 [target.'cfg(not(target_arch = "wasm32"))'.dependencies]
 tokio = { version = "1.36.0", features = ["full"] }
diff --git a/src/lib.rs b/src/lib.rs
index dea9c9c..0d1a4eb 100644
--- a/src/lib.rs
+++ b/src/lib.rs
@@ -107,7 +107,8 @@ pub struct State {
     window: Window,
     render_pipeline: wgpu::RenderPipeline,
     vertex_buffer: wgpu::Buffer,
-    num_vertices: u32,
+    index_buffer: wgpu::Buffer,
+    num_indices: u32,
 }
 
 impl State {
@@ -198,6 +199,14 @@ impl State {
             usage: wgpu::BufferUsages::VERTEX,
         });
 
+        let index_buffer = device.create_buffer_init(&wgpu::util::BufferInitDescriptor {
+            label: Some("Index Buffer"),
+            contents: bytemuck::cast_slice(INDICES),
+            usage: wgpu::BufferUsages::INDEX,
+        });
+
+        let num_indices = INDICES.len() as u32;
+
         let render_pipeline = device.create_render_pipeline(&wgpu::RenderPipelineDescriptor {
             label: Some("Render Pipeline"),
             layout: Some(&render_pipeline_layout),
@@ -238,8 +247,6 @@ impl State {
             multiview: None, // 5.
         });
 
-        let num_vertices = VERTICES.len() as u32;
-
         Self {
             window,
             surface,
@@ -249,7 +256,8 @@ impl State {
             size,
             render_pipeline,
             vertex_buffer,
-            num_vertices,
+            index_buffer,
+            num_indices,
         }
     }
 
@@ -306,9 +314,10 @@ impl State {
                 timestamp_writes: None,
             });
 
-            render_pass.set_pipeline(&self.render_pipeline); // 2.
+            render_pass.set_pipeline(&self.render_pipeline);
             render_pass.set_vertex_buffer(0, self.vertex_buffer.slice(..));
-            render_pass.draw(0..3, 0..1);
+            render_pass.set_index_buffer(self.index_buffer.slice(..), wgpu::IndexFormat::Uint16); // 1.
+            render_pass.draw_indexed(0..self.num_indices, 0, 0..1); // 2.
         }
 
         // submit will accept anything that implements IntoIter
@@ -347,17 +356,18 @@ impl Vertex {
     }
 }
 
+#[rustfmt::skip]
 const VERTICES: &[Vertex] = &[
-    Vertex {
-        position: [0.0, 0.5, 0.0],
-        color: [1.0, 0.0, 0.0],
-    },
-    Vertex {
-        position: [-0.5, -0.5, 0.0],
-        color: [0.0, 1.0, 0.0],
-    },
-    Vertex {
-        position: [0.5, -0.5, 0.0],
-        color: [0.0, 0.0, 1.0],
-    },
+    Vertex { position: [-0.0868241, 0.49240386, 0.0], color: [0.5, 0.0, 0.5] }, // A
+    Vertex { position: [-0.49513406, 0.06958647, 0.0], color: [0.5, 0.0, 0.5] }, // B
+    Vertex { position: [-0.21918549, -0.44939706, 0.0], color: [0.5, 0.0, 0.5] }, // C
+    Vertex { position: [0.35966998, -0.3473291, 0.0], color: [0.5, 0.0, 0.5] }, // D
+    Vertex { position: [0.44147372, 0.2347359, 0.0], color: [0.5, 0.0, 0.5] }, // E
+];
+
+#[rustfmt::skip]
+const INDICES: &[u16] = &[
+    0, 1, 4,
+    1, 2, 4,
+    2, 3, 4,
 ];