From f0c335d837a2a3f48161c9d4020a7d2d8bcb7077 Mon Sep 17 00:00:00 2001
From: Cassie Jones <code@witchoflight.com>
Date: Fri, 31 Jan 2020 05:13:41 -0500
Subject: [PATCH] Add velocities and padding to the particle data
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For now I'm using 2 vec4 of padding because LÖVR's ShaderBlock API
doesn't know about struct types or non-square matrices, and I need a
type which can hold 2 vec4, so I just pretend I'm sending a mat4 and
receive it as a struct of 4 vec4 on the shader side.
---
 README.md              |  8 ++++++++
 main.lua               | 19 ++++++++++++-------
 shaders/particles.frag |  3 ++-
 shaders/particles.vert | 15 ++++++++++++---
 4 files changed, 34 insertions(+), 11 deletions(-)
 create mode 100644 README.md

diff --git a/README.md b/README.md
new file mode 100644
index 0000000..7693d1b
--- /dev/null
+++ b/README.md
@@ -0,0 +1,8 @@
+# Particles :D
+
+I've never used compute shaders before, and so I wanted to play with them
+since I had watched some YouTube videos about them, and LÖVR had a really
+convenient API for use them.
+
+This uses Shader Storage Buffers for transferring particle data, and for
+simulating particle physics with compute shaders!
diff --git a/main.lua b/main.lua
index 78b666d..a9476a9 100644
--- a/main.lua
+++ b/main.lua
@@ -13,13 +13,13 @@ function lovr.load()
     features = lovr.graphics.getFeatures()
     shaders.particles = lovr.graphics.newShader("shaders/particles.vert", "shaders/particles.frag")
     blocks.particles = lovr.graphics.newShaderBlock("compute", {
-        particleData = {"vec4", nParticles},
+        particles = {"mat4", nParticles},
     }, { readable = true, writable = true })
-    shaders.particles:sendBlock('particleDataBuffer', blocks.particles)
+    shaders.particles:sendBlock('particleData', blocks.particles)
     shaders.particles:send("batchSize", batchSize)
     meshes.particle = makeParticleMesh(batchSize)
     local initial = initialParticleData(nParticles, range(-2, 2), range(0, 4), range(-2, 2), range(0.005, 0.01))
-    blocks.particles:send("particleData", initial)
+    blocks.particles:send("particles", initial)
 end
 
 function lovr.draw()
@@ -35,7 +35,7 @@ function lovr.draw()
     end
 
     withDepthTest("lequal", false, function()
-        lovr.graphics.setColor(0, 0.5, 1)
+        lovr.graphics.setColor(1, 1, 1)
         lovr.graphics.setShader(shaders.particles)
         meshes.particle:draw(mat4(), batches)
     end)
@@ -72,12 +72,17 @@ function range(min, max)
 end
 
 function initialParticleData(size, xRange, yRange, zRange, sRange)
-    local positions = {}
+    local particles = {}
     local insert = table.insert
     for i = 1, size do
-        insert(positions, {xRange(), yRange(), zRange(), sRange()})
+        insert(particles, {
+            xRange(), yRange(), zRange(), sRange(),
+            xRange(), yRange(), zRange(), 1,
+            0, 0, 0, 0,
+            0, 0, 0, 0,
+        })
     end
-    return positions
+    return particles
 end
 
 function withDepthTest(compareMode, write, callback)
diff --git a/shaders/particles.frag b/shaders/particles.frag
index 67f73bb..5c0f85d 100644
--- a/shaders/particles.frag
+++ b/shaders/particles.frag
@@ -1,7 +1,8 @@
 in vec2 uv;
+in vec4 particleColor;
 
 vec4 color(vec4 graphicsColor, sampler2D image, vec2 _uv) {
   float alpha = 1.0 - (distance(uv, vec2(0.5)) * 2.0);
   graphicsColor.a *= alpha;
-  return graphicsColor;
+  return graphicsColor * particleColor;
 }
diff --git a/shaders/particles.vert b/shaders/particles.vert
index d5ca089..b40c094 100644
--- a/shaders/particles.vert
+++ b/shaders/particles.vert
@@ -1,13 +1,22 @@
 in vec2 vertPosition;
 out vec2 uv;
+out vec4 particleColor;
 uniform vec3 headPos;
 uniform int batchSize;
-layout(std430) buffer particleDataBuffer { vec4 particleData[]; };
+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[]; };
 
 vec4 position(mat4 projection, mat4 transform, vec4 vertex) {
   int index = gl_VertexID / 4 + gl_InstanceID * batchSize;
-  vec3 pos = particleData[index].xyz;
-  float size = particleData[index].w;
+  particle_t particle = particles[index];
+  vec3 pos = particle.positionAndSize.xyz;
+  float size = particle.positionAndSize.w;
+  particleColor = particle.velocity;
   uv = vertPosition * 0.5 + 0.5;
 
   vec3 forward = normalize(pos - headPos);
-- 
2.47.0