Hacky D2Q9 BGK LBM on GPU using GLSL compute shaders

Improvised on top of computicles's scaffolding.

Works in a world where _works_ is defined as "displays stuff on screen that invokes thoughts of fluid movement".

4 files changed, 138 insertions, 0 deletions

diff --git a/src/shader/code/collide.glsl b/src/shader/code/collide.glsl
new file mode 100644
index 0000000..67e762b
--- /dev/null
+++ b/src/shader/code/collide.glsl
@@ -0,0 +1,95 @@
+static const std::string COLLIDE_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[]; };
+
+float get(uint x, uint y, int i, int j) {
+	return collideCells[9*128*y + 9*x + (i+1)*3 + j+1];
+}
+
+void set(uint x, uint y, int i, int j, float v) {
+	collideCells[9*128*y + 9*x + (i+1)*3 + j+1] = v;
+}
+
+void setFluid(uint x, uint y, vec2 v, float d) {
+	fluidCells[3*128*y + 3*x + 0] = float(x)-64. + 10.*v.x;
+	fluidCells[3*128*y + 3*x + 1] = float(y)-64. + 10.*v.y;
+	fluidCells[3*128*y + 3*x + 2] = d;
+}
+
+float density(uint x, uint y) {
+	return collideCells[9*128*y + 9*x + 0]
+	     + collideCells[9*128*y + 9*x + 1]
+	     + collideCells[9*128*y + 9*x + 2]
+	     + collideCells[9*128*y + 9*x + 3]
+	     + collideCells[9*128*y + 9*x + 4]
+	     + collideCells[9*128*y + 9*x + 5]
+	     + collideCells[9*128*y + 9*x + 6]
+	     + collideCells[9*128*y + 9*x + 7]
+	     + collideCells[9*128*y + 9*x + 8];
+}
+
+vec2 velocity(uint x, uint y, float d) {
+	return 1./d * vec2(
+		get(x,y, 1, 0) - get(x,y,-1, 0) + get(x,y, 1, 1) - get(x,y,-1,-1) + get(x,y, 1,-1) - get(x,y,-1,1),
+		get(x,y, 0, 1) - get(x,y, 0,-1) + get(x,y, 1, 1) - get(x,y,-1,-1) - get(x,y, 1,-1) + get(x,y,-1,1)
+	);
+}
+
+float w(int i, int j) {
+	if ( i == -1 ) {
+		if ( j != 0 ) {
+			return 1./36.;
+		} else {
+			return 1./9.;
+		}
+	} else if ( i == 0 ) {
+		if ( j != 0 ) {
+			return 1./9.;
+		} else {
+			return 4./9.;
+		}
+	} else {
+		if ( j != 0 ) {
+			return 1./36.;
+		} else {
+			return 1./9.;
+		}
+	}
+}
+
+float comp(int x, int y, vec2 v) {
+	return x*v.x + y*v.y;
+}
+
+float sq(float x) {
+	return x*x;
+}
+
+float norm(vec2 v) {
+	return sqrt(sq(v.x)+sq(v.y));
+}
+
+void main() {
+	const uint x = gl_GlobalInvocationID.x;
+	const uint y = gl_GlobalInvocationID.y;
+
+	const float omega = 0.6;
+
+	const float d = density(x,y);
+	const vec2  v = velocity(x,y,d);
+
+	setFluid(x,y,v,d);
+
+	for ( int i = -1; i <= 1; ++i ) {
+		for ( int j = -1; j <= 1; ++j ) {
+			const float eq = w(i,j) * d * (1 + 3*comp(i,j,v) + 4.5*sq(comp(i,j,v)) - 1.5*sq(norm(v)));
+			set(x,y,i,j, get(x,y,i,j) + omega * (eq - get(x,y,i,j)));
+		}
+	}
+
+}
+)";
diff --git a/src/shader/code/fragment.glsl b/src/shader/code/fragment.glsl
new file mode 100644
index 0000000..37e18bd
--- /dev/null
+++ b/src/shader/code/fragment.glsl
@@ -0,0 +1,5 @@
+static const std::string FRAGMENT_SHADER_CODE = R"(
+void main() {
+	gl_FragColor = gl_Color;
+}
+)";
diff --git a/src/shader/code/stream.glsl b/src/shader/code/stream.glsl
new file mode 100644
index 0000000..7dd5ba8
--- /dev/null
+++ b/src/shader/code/stream.glsl
@@ -0,0 +1,30 @@
+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[]; };
+
+float get(uint x, uint y, int i, int j) {
+	return collideCells[9*128*y + 9*x + (i+1)*3 + j+1];
+}
+
+void set(uint x, uint y, int i, int j, float v) {
+	streamCells[9*128*y + 9*x + (i+1)*3 + j+1] = v;
+}
+
+void main() {
+	const uint x = gl_GlobalInvocationID.x;
+	const uint y = gl_GlobalInvocationID.y;
+
+	if ( x != 0 && x != 128-1 && y != 0 && y != 128-1 ) {
+		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));
+			}
+		}
+	} else {
+
+	}
+}
+)";
diff --git a/src/shader/code/vertex.glsl b/src/shader/code/vertex.glsl
new file mode 100644
index 0000000..4c307d8
--- /dev/null
+++ b/src/shader/code/vertex.glsl
@@ -0,0 +1,8 @@
+static const std::string VERTEX_SHADER_CODE = R"(
+uniform mat4 MVP;
+
+void main() {
+	gl_Position = MVP * vec4(gl_Vertex.xy, 0.0, 1.0);
+	gl_FrontColor = vec4(1., 0., 0., 0.);
+}
+)";