From e017b675d96c58924071ca6c739bbd7910a2b2b4 Mon Sep 17 00:00:00 2001
From: Micha White <botahamec@outlook.com>
Date: Mon, 17 Oct 2022 22:45:31 -0400
Subject: Depth ordering

---
 src/instance.rs | 12 ++++++++----
 1 file changed, 8 insertions(+), 4 deletions(-)

(limited to 'src/instance.rs')

diff --git a/src/instance.rs b/src/instance.rs
index bacad56..2bff797 100644
--- a/src/instance.rs
+++ b/src/instance.rs
@@ -21,7 +21,7 @@ pub struct Instance {
 	/// Rotation, in radians
 	pub rotation: f32,
 	/// z-index
-	pub z_index: u32, // TODO something more interesting with z-axis
+	pub z_index: f32,
 }
 
 impl Default for Instance {
@@ -30,7 +30,7 @@ impl Default for Instance {
 			position: [0.0; 2],
 			size: [1.0; 2],
 			rotation: 0.0,
-			z_index: 0,
+			z_index: 0.0,
 			texture_coordinates: [0.0; 2],
 			texture_size: [1.0; 2],
 			texture_atlas_index: 0,
@@ -42,7 +42,7 @@ impl Instance {
 	// whenever this is updated, please also update `sprite.wgsl`
 	const ATTRIBUTES: [wgpu::VertexAttribute; 7] = wgpu::vertex_attr_array![
 		1 => Float32x2, 2 => Float32x2, 3 => Float32x2, 4 => Float32x2,
-		5 => Uint32, 6 => Float32, 7 => Uint32
+		5 => Uint32, 6 => Float32, 7 => Float32
 	];
 
 	pub(crate) fn desc<'a>() -> wgpu::VertexBufferLayout<'a> {
@@ -135,10 +135,14 @@ impl InstanceBuffer {
 			self.expand_buffer(device);
 		}
 
+		// the instances must be sorted by z-index before being handed to the GPU
+		let mut sorted = self.instances.clone();
+		sorted.sort_by(|a, b| a.z_index.total_cmp(&b.z_index));
+
 		queue.write_buffer(
 			&self.instance_buffer,
 			0 as wgpu::BufferAddress,
-			bytemuck::cast_slice(&self.instances),
+			bytemuck::cast_slice(&sorted),
 		);
 	}
 }
-- 
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