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

---
 shaders/sprite.wgsl | 25 +++++++++++++++++++++++--
 1 file changed, 23 insertions(+), 2 deletions(-)

(limited to 'shaders')

diff --git a/shaders/sprite.wgsl b/shaders/sprite.wgsl
index d126cae..b8ce42b 100644
--- a/shaders/sprite.wgsl
+++ b/shaders/sprite.wgsl
@@ -3,14 +3,35 @@ struct VertexInput {
 	@location(0) position: vec2<f32>
 }
 
+struct InstanceInput {
+	@location(1) position: vec2<f32>,
+	@location(2) size: vec2<f32>,
+	@location(3) rotation: f32,
+	@location(4) z_layer: i32
+}
+
 struct VertexOutput {
 	@builtin(position) clip_position: vec4<f32>
 }
 
 @vertex
-fn vs_main(model: VertexInput) -> VertexOutput {
+fn vs_main(model: VertexInput, instance: InstanceInput) -> VertexOutput {
 	var out: VertexOutput;
-	out.clip_position = vec4<f32>(model.position, 0.0, 1.0);
+
+	// rotate the sprite
+	let a = vec2<f32>(cos(instance.rotation), sin(instance.rotation));
+	let b = vec2<f32>(-a[1], a[0]);
+	let rotation = mat2x2<f32>(a, b);
+	let rotated = rotation * model.position;
+
+	// scale the sprite
+	let x = rotated[0] * instance.size[0];
+	let y = rotated[1] * instance.size[1];
+
+	// move the sprite
+	let position = vec2<f32>(x, y) + instance.position;
+
+	out.clip_position = vec4<f32>(position, f32(instance.z_layer), 1.0);
 	return out;
 }
 
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