Extract interaction logic into separate shader

The collide shader became to crowded for my taste.

As a nice side benefit we can now execute interaction processing only
when actual interaction is taking place.

3 files changed, 158 insertions, 86 deletions

diff --git a/src/main.cc b/src/main.cc
index 4621d30..2a3dd9b 100644
--- a/src/main.cc
+++ b/src/main.cc
@@ -18,6 +18,7 @@
 #include "shader/code/vertex.glsl"
 #include "shader/code/fragment.glsl"
 
+#include "shader/code/interact.glsl"
 #include "shader/code/collide.glsl"
 #include "shader/code/stream.glsl"
 
@@ -67,6 +68,7 @@ int renderWindow() {
 	std::unique_ptr<LatticeCellBuffer> lattice_b;
 	std::unique_ptr<FluidCellBuffer>   fluid;
 
+	std::unique_ptr<ComputeShader> interact_shader;
 	std::unique_ptr<ComputeShader> collide_shader;
 	std::unique_ptr<ComputeShader> stream_shader;
 
@@ -87,11 +89,12 @@ int renderWindow() {
 			return 1; // everything shall be fluid
 		});
 
-		collide_shader = std::make_unique<ComputeShader>(COLLIDE_SHADER_CODE);
-		stream_shader  = std::make_unique<ComputeShader>(STREAM_SHADER_CODE);
+		interact_shader = std::make_unique<ComputeShader>(INTERACT_SHADER_CODE);
+		collide_shader  = std::make_unique<ComputeShader>(COLLIDE_SHADER_CODE);
+		stream_shader   = std::make_unique<ComputeShader>(STREAM_SHADER_CODE);
 	});
 
-	if ( !collide_shader->isGood() || !stream_shader->isGood() ) {
+	if ( !interact_shader->isGood() || !collide_shader->isGood() || !stream_shader->isGood() ) {
 		std::cerr << "Compute shader error." << std::endl;
 		return -1;
 	}
@@ -125,30 +128,40 @@ int renderWindow() {
 				if ( tick ) {
 					collide_shader->workOn(tick_buffers);
 					stream_shader->workOn(tick_buffers);
+					interact_shader->workOn(tick_buffers);
 					tick = false;
 				} else {
 					collide_shader->workOn(tock_buffers);
 					stream_shader->workOn(tock_buffers);
+					interact_shader->workOn(tock_buffers);
 					tick = true;
 				}
 
-				{
-					auto guard = collide_shader->use();
+				/// Handle mouse-based interaction
+				const auto m = window.getMouse();
 
-					collide_shader->setUniform("prevMouseState", prevLatticeMouseState);
-					collide_shader->setUniform("prevMousePos", prevLatticeMouseX, prevLatticeMouseY);
+				if ( std::get<0>(m) != 0 || prevLatticeMouseState != 0 ) {
+					auto guard = interact_shader->use();
+
+					interact_shader->setUniform("prevMouseState", prevLatticeMouseState);
+					interact_shader->setUniform("prevMousePos", prevLatticeMouseX, prevLatticeMouseY);
 
-					const auto m = window.getMouse();
 					const float latticeMouseX = float(std::get<1>(m)) / window.getWidth()  * world_width  + nX/2;
 					const float latticeMouseY = float(std::get<2>(m)) / window.getHeight() * world_height + nY/2;
 
-					collide_shader->setUniform("currMouseState", std::get<0>(m));
-					collide_shader->setUniform("currMousePos", latticeMouseX, latticeMouseY);
+					interact_shader->setUniform("currMouseState", std::get<0>(m));
+					interact_shader->setUniform("currMousePos", latticeMouseX, latticeMouseY);
 
 					prevLatticeMouseState = std::get<0>(m);
 					prevLatticeMouseX = latticeMouseX;
 					prevLatticeMouseY = latticeMouseY;
 
+					interact_shader->dispatch(nX, nY);
+				}
+
+				/// Perform collide & stream steps
+				{
+					auto guard = collide_shader->use();
 					collide_shader->dispatch(nX, nY);
 				}
 				{
diff --git a/src/shader/code/collide.glsl b/src/shader/code/collide.glsl
index a73024e..0ddae7b 100644
--- a/src/shader/code/collide.glsl
+++ b/src/shader/code/collide.glsl
@@ -7,13 +7,6 @@ layout (std430, binding=1) buffer bufferCollide  { float collideCells[];  };
 layout (std430, binding=2) buffer bufferStream   { float streamCells[];   };
 layout (std430, binding=3) buffer bufferFluid    { float fluidCells[];    };
 
-/// external influence
-
-uniform int  prevMouseState;
-uniform vec2 prevMousePos;
-uniform int  currMouseState;
-uniform vec2 currMousePos;
-
 /// LBM constants
 
 uniform uint nX;
@@ -43,22 +36,6 @@ float norm(vec2 v) {
 	return sqrt(dot(v,v));
 }
 
-float distanceToLineSegment(vec2 a, vec2 b, vec2 p) {
-	const vec2 ab = b - a;
-
-	const vec2 pa = a - p;
-	if ( dot(ab, pa) > 0.0 ) {
-		return norm(pa);
-	}
-
-	const vec2 bp = p - b;
-	if ( dot(ab, bp) > 0.0 ) {
-		return norm(bp);
-	}
-
-	return norm(pa - ab * (dot(ab, pa) / dot(ab, ab)));
-}
-
 /// Array indexing
 
 uint indexOfDirection(int i, int j) {
@@ -98,11 +75,6 @@ int getMaterial(uint x, uint y) {
 	return int(fluidCells[idx + 2]);
 }
 
-void setMaterial(uint x, uint y, int m) {
-	const uint idx = indexOfFluidVertex(x, y);
-	fluidCells[idx + 2] = m;
-}
-
 /// Moments
 
 float density(uint x, uint y) {
@@ -127,50 +99,19 @@ float equilibrium(float d, vec2 v, int i, int j) {
 	return w(i,j) * d * (1 + 3*comp(i,j,v) + 4.5*sq(comp(i,j,v)) - 1.5*sq(norm(v)));
 }
 
-/// Disable wall interior
-
-void disableWallInterior(uint x, uint y) {
-	int wallNeighbors = 0;
-
-	for ( int i = -1; i <= 1; ++i ) {
-		for ( int j = -1; j <= 1; ++j ) {
-			const int material = getMaterial(x+i,y+j);
-			if ( material  == 0 || material == 2 || material == 3 ) {
-				++wallNeighbors;
-			}
-		}
-	}
+/// Material number meaning (geometry is only changed by the interaction shader)
 
-	if ( wallNeighbors == 9 ) {
-		setMaterial(x,y,0);
-	}
-}
-
-/// Determine external influence
-
-bool isNearMouse(uint x, uint y, float eps) {
-	if ( prevMouseState == currMouseState ) {
-		return distanceToLineSegment(prevMousePos, currMousePos, vec2(x,y)) < eps;
-	} else {
-		return norm(vec2(x,y) - currMousePos) < eps;
-	}
+bool isBulkFluidCell(int material) {
+	return material == 1 || material == 4;
 }
 
-float getExternalPressureInflux(uint x, uint y) {
-	if ( currMouseState == 1 && isNearMouse(x, y, 3) ) {
+float getExternalMassInflux(int material) {
+	if ( material == 4 ) {
 		return 1.5;
 	} else {
 		return 0.0;
 	}
-}
-
-bool isWallRequestedAt(uint x, uint y) {
-	if ( currMouseState == 2 && isNearMouse(x, y, 3) ) {
-		return true;
-	} else {
-		return false;
-	}
-}
+};
 
 /// Actual collide kernel
 
@@ -184,17 +125,8 @@ void main() {
 
 	const int material = getMaterial(x,y);
 
-	if ( isWallRequestedAt(x,y) && material == 1 ) {
-		setMaterial(x,y,3);
-		return;
-	}
-
-	if ( material == 3 ) { // manually added wall
-		disableWallInterior(x,y);
-	}
-
-	if ( material == 1 ) { // fluid
-		const float d = max(getExternalPressureInflux(x,y), density(x,y));
+	if ( isBulkFluidCell(material) ) {
+		const float d = max(density(x,y), getExternalMassInflux(material));
 		const vec2  v = velocity(x,y,d);
 
 		setFluid(x,y,v);
diff --git a/src/shader/code/interact.glsl b/src/shader/code/interact.glsl
new file mode 100644
index 0000000..a65d96a
--- /dev/null
+++ b/src/shader/code/interact.glsl
@@ -0,0 +1,127 @@
+static const std::string INTERACT_SHADER_CODE = R"(
+#version 430
+
+layout (local_size_x = 1, local_size_y = 1) in;
+
+layout (std430, binding=3) buffer bufferFluid { float fluidCells[]; };
+
+uniform uint nX;
+uniform uint nY;
+
+/// External influence
+
+uniform int  prevMouseState;
+uniform vec2 prevMousePos;
+uniform int  currMouseState;
+uniform vec2 currMousePos;
+
+/// Vector utilities
+
+float norm(vec2 v) {
+	return sqrt(dot(v,v));
+}
+
+float distanceToLineSegment(vec2 a, vec2 b, vec2 p) {
+	const vec2 ab = b - a;
+
+	const vec2 pa = a - p;
+	if ( dot(ab, pa) > 0.0 ) {
+		return norm(pa);
+	}
+
+	const vec2 bp = p - b;
+	if ( dot(ab, bp) > 0.0 ) {
+		return norm(bp);
+	}
+
+	return norm(pa - ab * (dot(ab, pa) / dot(ab, ab)));
+}
+
+/// Array indexing
+
+uint indexOfFluidVertex(uint x, uint y) {
+	return 3*nX*y + 3*x;
+}
+
+/// Data access
+
+int getMaterial(uint x, uint y) {
+	const uint idx = indexOfFluidVertex(x, y);
+	return int(fluidCells[idx + 2]);
+}
+
+void setMaterial(uint x, uint y, int m) {
+	const uint idx = indexOfFluidVertex(x, y);
+	fluidCells[idx + 2] = m;
+}
+
+/// Geometry cleanup
+
+void disableWallInterior(uint x, uint y) {
+	int wallNeighbors = 0;
+
+	for ( int i = -1; i <= 1; ++i ) {
+		for ( int j = -1; j <= 1; ++j ) {
+			const int material = getMaterial(x+i,y+j);
+			if ( material  == 0 || material == 2 || material == 3 ) {
+				++wallNeighbors;
+			}
+		}
+	}
+
+	if ( wallNeighbors == 9 ) {
+		setMaterial(x,y,0);
+	}
+}
+
+/// Determine external influence
+
+bool isNearMouse(uint x, uint y, float eps) {
+	if ( prevMouseState == currMouseState ) {
+		return distanceToLineSegment(prevMousePos, currMousePos, vec2(x,y)) < eps;
+	} else {
+		return norm(vec2(x,y) - currMousePos) < eps;
+	}
+}
+
+bool isInfluxRequestedAt(uint x, uint y) {
+	return currMouseState == 1 && isNearMouse(x, y, 3);
+}
+
+bool isWallRequestedAt(uint x, uint y) {
+	return currMouseState == 2 && isNearMouse(x, y, 3);
+}
+
+/// Actual interaction 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 == 1 ) {
+		if ( isInfluxRequestedAt(x,y) ) {
+			setMaterial(x,y,4);
+			return;
+		}
+		if ( isWallRequestedAt(x,y) ) {
+			setMaterial(x,y,3);
+			return;
+		}
+	}
+
+	if ( material == 3 ) {
+		disableWallInterior(x,y);
+	}
+
+	if ( material == 4 ) {
+		// reset influx material after execution
+		setMaterial(x,y,1);
+	}
+}
+)";