From 1ab5f3db018a3169ad6074fc2b75d44c3a45dd16 Mon Sep 17 00:00:00 2001
From: Adrian Kummerlaender
Date: Sun, 24 Feb 2019 12:25:08 +0100
Subject: Smoothen mouse interaction

---
 src/main.cc                  | 15 +++++++++++++--
 src/shader/code/collide.glsl | 36 +++++++++++++++++++++++++++++++-----
 2 files changed, 44 insertions(+), 7 deletions(-)

diff --git a/src/main.cc b/src/main.cc
index c9fb347..4621d30 100644
--- a/src/main.cc
+++ b/src/main.cc
@@ -106,6 +106,10 @@ int renderWindow() {
 	auto tick_buffers = { lattice_a->getBuffer(), lattice_b->getBuffer(), fluid->getBuffer() };
 	auto tock_buffers = { lattice_b->getBuffer(), lattice_a->getBuffer(), fluid->getBuffer() };
 
+	int prevLatticeMouseState = 0;
+	int prevLatticeMouseX = 0;
+	int prevLatticeMouseY = 0;
+
 	window.render([&](bool window_size_changed) {
 		if ( pause_key.wasClicked() ) {
 			update_lattice = !update_lattice;
@@ -131,12 +135,19 @@ int renderWindow() {
 				{
 					auto guard = collide_shader->use();
 
+					collide_shader->setUniform("prevMouseState", prevLatticeMouseState);
+					collide_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("mouseState", std::get<0>(m));
-					collide_shader->setUniform("mousePos", latticeMouseX, latticeMouseY);
+					collide_shader->setUniform("currMouseState", std::get<0>(m));
+					collide_shader->setUniform("currMousePos", latticeMouseX, latticeMouseY);
+
+					prevLatticeMouseState = std::get<0>(m);
+					prevLatticeMouseX = latticeMouseX;
+					prevLatticeMouseY = latticeMouseY;
 
 					collide_shader->dispatch(nX, nY);
 				}
diff --git a/src/shader/code/collide.glsl b/src/shader/code/collide.glsl
index 3f4e2c5..a73024e 100644
--- a/src/shader/code/collide.glsl
+++ b/src/shader/code/collide.glsl
@@ -9,8 +9,10 @@ layout (std430, binding=3) buffer bufferFluid    { float fluidCells[];    };
 
 /// external influence
 
-uniform int  mouseState;
-uniform vec2 mousePos;
+uniform int  prevMouseState;
+uniform vec2 prevMousePos;
+uniform int  currMouseState;
+uniform vec2 currMousePos;
 
 /// LBM constants
 
@@ -38,7 +40,23 @@ float sq(float x) {
 }
 
 float norm(vec2 v) {
-	return sqrt(sq(v.x)+sq(v.y));
+	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
@@ -130,8 +148,16 @@ void disableWallInterior(uint x, uint y) {
 
 /// 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;
+	}
+}
+
 float getExternalPressureInflux(uint x, uint y) {
-	if ( mouseState == 1 && norm(vec2(x,y) - mousePos) < 2 ) {
+	if ( currMouseState == 1 && isNearMouse(x, y, 3) ) {
 		return 1.5;
 	} else {
 		return 0.0;
@@ -139,7 +165,7 @@ float getExternalPressureInflux(uint x, uint y) {
 }
 
 bool isWallRequestedAt(uint x, uint y) {
-	if ( mouseState == 2 && norm(vec2(x,y) - mousePos) < 2 ) {
+	if ( currMouseState == 2 && isNearMouse(x, y, 3) ) {
 		return true;
 	} else {
 		return false;
-- 
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