Tidy up streaming and bounce back boundary handling

Introduce a inactive receive-only outer boundary to simplify streaming.
Extract and generalize bounce back handling. Further work will require
tracking cell _material_ to enable both easier definition and dynamic
updating of the geometry.

1 files changed, 18 insertions, 0 deletions

diff --git a/src/shader/code/collide.glsl b/src/shader/code/collide.glsl
index 23e98f9..cb950cb 100644
--- a/src/shader/code/collide.glsl
+++ b/src/shader/code/collide.glsl
@@ -110,6 +110,16 @@ float getExternalPressureInflux(uint x, uint y) {
 	}
 }
 
+/// Domain description
+
+bool isEndOfWorld(uint x, uint y) {
+	return x == 0 || x == nX-1 || y == 0 || y == nY-1;
+}
+
+bool isOuterWall(uint x, uint y) {
+	return x == 1 || x == nX-2 || y == 1 || y == nY-2;
+}
+
 /// Actual collide kernel
 
 void main() {
@@ -120,6 +130,14 @@ void main() {
 		return;
 	}
 
+	if ( isEndOfWorld(x,y) ) {
+		return;
+	}
+
+	if ( isOuterWall(x,y) ) {
+		return;
+	}
+
 	const float d = max(getExternalPressureInflux(x,y), density(x,y));
 	const vec2  v = velocity(x,y,d);