From 26c1cf58f483e64d80703fe37c4bd3923d1ff5b7 Mon Sep 17 00:00:00 2001
From: Adrian Kummerlaender
Date: Mon, 25 Feb 2019 19:57:11 +0100
Subject: Merge streaming into collide shader

i.e. implement the A-B pattern.

Dispatching only one compute shader per interaction-less simulation step
already yields very noticeable performance gains. All cell types are now
fully handled by the collide shader which further simplifies the code.
---
 src/shader/code/collide.glsl | 36 ++++++++++++++-----
 src/shader/code/stream.glsl  | 82 --------------------------------------------
 2 files changed, 28 insertions(+), 90 deletions(-)
 delete mode 100644 src/shader/code/stream.glsl

(limited to 'src/shader')

diff --git a/src/shader/code/collide.glsl b/src/shader/code/collide.glsl
index 673a285..4efd7fb 100644
--- a/src/shader/code/collide.glsl
+++ b/src/shader/code/collide.glsl
@@ -61,7 +61,7 @@ float get(uint x, uint y, int i, int j) {
 }
 
 void set(uint x, uint y, int i, int j, float v) {
-	collideCells[indexOfLatticeCell(x,y) + indexOfDirection(i,j)] = v;
+	streamCells[indexOfLatticeCell(x,y) + indexOfDirection(i,j)] = v;
 }
 
 void setFluid(uint x, uint y, vec2 v) {
@@ -105,6 +105,18 @@ bool isBulkFluidCell(int material) {
 	return material == 1 || material == 4 || material == 5 || material == 6;
 }
 
+bool isBounceBackCell(int material) {
+	return material == 2 || material == 3;
+}
+
+bool isInflowCell(int material) {
+	return material == 5;
+}
+
+bool isOutflowCell(int material) {
+	return material == 6;
+}
+
 float getExternalMassInflux(int material) {
 	if ( material == 4 ) {
 		return 1.5;
@@ -113,7 +125,7 @@ float getExternalMassInflux(int material) {
 	}
 };
 
-/// Actual collide kernel
+/// Actual collide&stream kernel
 
 void main() {
 	const uint x = gl_GlobalInvocationID.x;
@@ -125,14 +137,14 @@ void main() {
 
 	const int material = getMaterial(x,y);
 
-	if ( isBulkFluidCell(material) ) {
-		float d = max(density(x,y), getExternalMassInflux(material));
-		vec2  v = velocity(x,y,d);
+	float d = max(density(x,y), getExternalMassInflux(material));
+	vec2  v = velocity(x,y,d);
 
-		if ( material == 5 ) {
+	if ( isBulkFluidCell(material) ) {
+		if ( isInflowCell(material) ) {
 			v = vec2(0.1,0.0);
 		}
-		if ( material == 6 ) {
+		if ( isOutflowCell(material) ) {
 			d = 1.0;
 		}
 
@@ -140,7 +152,15 @@ void main() {
 
 		for ( int i = -1; i <= 1; ++i ) {
 			for ( int j = -1; j <= 1; ++j ) {
-				set(x,y,i,j, get(x,y,i,j) + omega * (equilibrium(d,v,i,j) - get(x,y,i,j)));
+				set(x+i,y+j,i,j, get(x,y,i,j) + omega * (equilibrium(d,v,i,j) - get(x,y,i,j)));
+			}
+		}
+	}
+
+	if ( isBounceBackCell(material) ) {
+		for ( int i = -1; i <= 1; ++i ) {
+			for ( int j = -1; j <= 1; ++j ) {
+				set(x+(-1)*i,y+(-1)*j,(-1)*i,(-1)*j, get(x,y,i,j) + omega * (equilibrium(d,v,i,j) - get(x,y,i,j)));
 			}
 		}
 	}
diff --git a/src/shader/code/stream.glsl b/src/shader/code/stream.glsl
deleted file mode 100644
index 59aed98..0000000
--- a/src/shader/code/stream.glsl
+++ /dev/null
@@ -1,82 +0,0 @@
-static const std::string STREAM_SHADER_CODE = R"(
-#version 430
-
-layout (local_size_x = 1, local_size_y = 1) in;
-
-layout (std430, binding=1) buffer bufferCollide  { float collideCells[];  };
-layout (std430, binding=2) buffer bufferStream   { float streamCells[];   };
-layout (std430, binding=3) buffer bufferFluid    { float fluidCells[];    };
-
-/// LBM constants
-
-uniform uint nX;
-uniform uint nY;
-
-const uint q = 9;
-
-// Array indexing
-
-uint indexOfDirection(int i, int j) {
-	return 3*(i+1) + (j+1);
-}
-
-uint indexOfLatticeCell(uint x, uint y) {
-	return q*nX*y + q*x;
-}
-
-uint indexOfFluidVertex(uint x, uint y) {
-	return 3*nX*y + 3*x;
-}
-
-/// Data access
-
-float get(uint x, uint y, int i, int j) {
-	return collideCells[indexOfLatticeCell(x,y) + indexOfDirection(i,j)];
-}
-
-void set(uint x, uint y, int i, int j, float v) {
-	streamCells[indexOfLatticeCell(x,y) + indexOfDirection(i,j)] = v;
-}
-
-int getMaterial(uint x, uint y) {
-	const uint idx = indexOfFluidVertex(x, y);
-	return int(fluidCells[idx + 2]);
-}
-
-/// Boundary conditions
-
-void bounceBack(uint x, uint y) {
-	for ( int i = -1; i <= 1; ++i ) {
-		for ( int j = -1; j <= 1; ++j ) {
-			set(x,y,i,j, get(x,y,(-1)*i,(-1)*j));
-		}
-	}
-}
-
-/// Actual stream kernel
-
-void main() {
-	const uint x = gl_GlobalInvocationID.x;
-	const uint y = gl_GlobalInvocationID.y;
-
-	if ( !(x < nX && y < nY) ) {
-		return;
-	}
-
-	const int material = getMaterial(x,y);
-
-	if ( material == 0 ) {
-		return;
-	}
-
-	if ( material == 2 || material == 3 ) {
-		bounceBack(x,y);
-	}
-
-	for ( int i = -1; i <= 1; ++i ) {
-		for ( int j = -1; j <= 1; ++j ) {
-			set(x+i,y+j,i,j, get(x,y,i,j));
-		}
-	}
-}
-)";
-- 
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