From d02366e9b8f8f7f53455580d933e550a7b06f112 Mon Sep 17 00:00:00 2001
From: Cassie Jones <code@witchoflight.com>
Date: Fri, 31 Jan 2020 07:48:01 -0500
Subject: [PATCH] Add basic compute simulation (disabled)

We want to use a compute shader to update the particle states.
Unfortunately, they don't want to be updated. If you uncomment the line
that runs the compute shader, all the particles turn into a glitchy
mess. Committing this code for reproducability's sake.
---
 main.lua               | 10 ++++++++++
 shaders/particles.comp | 15 +++++++++++++++
 2 files changed, 25 insertions(+)
 create mode 100644 shaders/particles.comp

diff --git a/main.lua b/main.lua
index a9476a9..9764877 100644
--- a/main.lua
+++ b/main.lua
@@ -8,16 +8,25 @@ local features
 local shaders = {}
 local blocks = {}
 local meshes = {}
+local compute = {}
 
 function lovr.load()
     features = lovr.graphics.getFeatures()
+
     shaders.particles = lovr.graphics.newShader("shaders/particles.vert", "shaders/particles.frag")
+
     blocks.particles = lovr.graphics.newShaderBlock("compute", {
         particles = {"mat4", nParticles},
     }, { readable = true, writable = true })
     shaders.particles:sendBlock('particleData', blocks.particles)
     shaders.particles:send("batchSize", batchSize)
+
     meshes.particle = makeParticleMesh(batchSize)
+
+    compute.particles = lovr.graphics.newComputeShader("shaders/particles.comp")
+    compute.particles:sendBlock('particleData', blocks.particles)
+    compute.particles:send("dt", 0.0)
+
     local initial = initialParticleData(nParticles, range(-2, 2), range(0, 4), range(-2, 2), range(0.005, 0.01))
     blocks.particles:send("particles", initial)
 end
@@ -25,6 +34,7 @@ end
 function lovr.draw()
     lovr.graphics.clear()
     local x, y, z = lovr.headset.getPose("head")
+    -- lovr.graphics.compute(compute.particles, batches)
     shaders.particles:send("headPos", {x, y, z})
 
     lovr.graphics.setColor(0.6, 0.1, 0)
diff --git a/shaders/particles.comp b/shaders/particles.comp
new file mode 100644
index 0000000..f2553ae
--- /dev/null
+++ b/shaders/particles.comp
@@ -0,0 +1,15 @@
+uniform float dt;
+struct particle_t {
+  vec4 positionAndSize;
+  vec4 velocity;
+  vec4 padding2; // for LÖVR's limited ShaderBlock type :(
+  vec4 padding3; // for LÖVR's limited ShaderBlock type :(
+};
+layout(std430) buffer particleData { particle_t particles[]; };
+
+layout(local_size_x = 128) in;
+void compute() {
+  uint particleId = gl_GlobalInvocationID.x;
+  particles[particleId].positionAndSize.xyz +=
+      particles[particleId].velocity.xyz * dt;
+}
-- 
2.43.2