From 83295e01008bdf25e03f6b5aa18b93b735a5e326 Mon Sep 17 00:00:00 2001
From: Micha White <botahamec@outlook.com>
Date: Sun, 18 Sep 2022 16:45:05 -0400
Subject: instancing

---
 src/instance.rs | 46 ++++++++++++++++++++++++++++++++++++++++++++++
 src/lib.rs      |  2 ++
 src/renderer.rs | 24 +++++++++++++++++++++---
 src/vertex.rs   |  5 ++++-
 4 files changed, 73 insertions(+), 4 deletions(-)
 create mode 100644 src/instance.rs

(limited to 'src')

diff --git a/src/instance.rs b/src/instance.rs
new file mode 100644
index 0000000..6de0133
--- /dev/null
+++ b/src/instance.rs
@@ -0,0 +1,46 @@
+use std::mem::size_of;
+
+use bytemuck::{Pod, Zeroable};
+
+#[repr(C)]
+#[derive(Copy, Clone, Debug, PartialEq, Pod, Zeroable)]
+pub struct Instance {
+	/// Position on the screen
+	pub position: [f32; 2],
+	/// Relative size
+	pub size: [f32; 2],
+	/// Rotation, in radians
+	pub rotation: f32,
+	/// z-index
+	pub z_index: i32,
+}
+
+impl Default for Instance {
+	fn default() -> Self {
+		Self {
+			position: [0.0; 2],
+			size: [1.0; 2],
+			rotation: 0.0,
+			z_index: 0,
+		}
+	}
+}
+
+impl Instance {
+	// whenever this is updated, please also update `sprite.wgsl`
+	const ATTRIBUTES: [wgpu::VertexAttribute; 4] =
+		wgpu::vertex_attr_array![1 => Float32x2, 2 => Float32x2, 3 => Float32, 4 => Sint32];
+
+	pub(crate) fn desc<'a>() -> wgpu::VertexBufferLayout<'a> {
+		// make sure these two don't conflict
+		debug_assert_eq!(
+			Self::ATTRIBUTES[0].shader_location as usize,
+			crate::Vertex::ATTRIBUTES.len()
+		);
+		wgpu::VertexBufferLayout {
+			array_stride: size_of::<Self>() as wgpu::BufferAddress,
+			step_mode: wgpu::VertexStepMode::Instance,
+			attributes: &Self::ATTRIBUTES,
+		}
+	}
+}
diff --git a/src/lib.rs b/src/lib.rs
index fbc517b..15f64b3 100644
--- a/src/lib.rs
+++ b/src/lib.rs
@@ -5,9 +5,11 @@
 #![allow(clippy::module_name_repetitions)]
 
 pub mod config;
+mod instance;
 pub mod renderer;
 mod vertex;
 
 pub use config::RenderWindowConfig;
+pub(crate) use instance::Instance;
 pub use renderer::Renderer;
 pub(crate) use vertex::Vertex;
diff --git a/src/renderer.rs b/src/renderer.rs
index dc8ecb2..75e6d1e 100644
--- a/src/renderer.rs
+++ b/src/renderer.rs
@@ -1,6 +1,6 @@
 use std::convert::TryInto;
 
-use crate::{vertex::SQUARE, RenderWindowConfig, Vertex};
+use crate::{vertex::SQUARE, Instance, RenderWindowConfig, Vertex};
 use pollster::FutureExt;
 use thiserror::Error;
 use wgpu::{include_wgsl, util::DeviceExt};
@@ -44,6 +44,7 @@ pub struct Renderer {
 	render_pipeline: wgpu::RenderPipeline,
 	square_vertex_buffer: wgpu::Buffer,
 	square_vertices: u32,
+	instances: Vec<Instance>,
 	window: Window,
 }
 
@@ -128,7 +129,7 @@ impl Renderer {
 			vertex: wgpu::VertexState {
 				module: &shader,
 				entry_point: "vs_main",
-				buffers: &[Vertex::desc()],
+				buffers: &[Vertex::desc(), Instance::desc()],
 			},
 			// information about the fragment shader
 			fragment: Some(wgpu::FragmentState {
@@ -171,6 +172,8 @@ impl Renderer {
 			usage: wgpu::BufferUsages::VERTEX,
 		});
 
+		let instances = Vec::new();
+
 		Ok(Self {
 			surface,
 			device,
@@ -179,6 +182,7 @@ impl Renderer {
 			render_pipeline,
 			square_vertex_buffer,
 			square_vertices,
+			instances,
 			window,
 		})
 	}
@@ -216,6 +220,19 @@ impl Renderer {
 				label: Some("Render Encoder"),
 			});
 
+		let num_instances = self
+			.instances
+			.len()
+			.try_into()
+			.expect("expected less than 3 billion instances");
+		let instance_buffer = self
+			.device
+			.create_buffer_init(&wgpu::util::BufferInitDescriptor {
+				label: Some("Sprite Instance Buffer"),
+				contents: bytemuck::cast_slice(&self.instances),
+				usage: wgpu::BufferUsages::VERTEX,
+			});
+
 		{
 			let mut render_pass = encoder.begin_render_pass(&wgpu::RenderPassDescriptor {
 				label: Some("Render Pass"),
@@ -232,7 +249,8 @@ impl Renderer {
 
 			render_pass.set_pipeline(&self.render_pipeline);
 			render_pass.set_vertex_buffer(0, self.square_vertex_buffer.slice(..));
-			render_pass.draw(0..self.square_vertices, 0..1);
+			render_pass.set_vertex_buffer(1, instance_buffer.slice(..));
+			render_pass.draw(0..self.square_vertices, 0..num_instances);
 		}
 		// the encoder can't finish building the command buffer until the
 		// render pass is dropped
diff --git a/src/vertex.rs b/src/vertex.rs
index 7735801..6514fd3 100644
--- a/src/vertex.rs
+++ b/src/vertex.rs
@@ -2,6 +2,7 @@ use std::mem::size_of;
 
 use bytemuck::{Pod, Zeroable};
 
+/// The vertices needed to form a square
 pub const SQUARE: [Vertex; 4] = [
 	Vertex::new(-0.5, -0.5),
 	Vertex::new(0.5, -0.5),
@@ -22,7 +23,9 @@ impl Vertex {
 }
 
 impl Vertex {
-	const ATTRIBUTES: [wgpu::VertexAttribute; 1] = wgpu::vertex_attr_array![0 => Float32x2];
+	// whenever this is updated, please also update `sprite.wgsl`
+	pub(crate) const ATTRIBUTES: [wgpu::VertexAttribute; 1] =
+		wgpu::vertex_attr_array![0 => Float32x2];
 
 	pub(crate) const fn desc<'a>() -> wgpu::VertexBufferLayout<'a> {
 		wgpu::VertexBufferLayout {
-- 
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