From 8067e0fa459c0d7edb2e4ed328b04fb4bba6c308 Mon Sep 17 00:00:00 2001
From: Eric Wasylishen <ewasylishen@gmail.com>
Date: Tue, 21 Feb 2017 01:25:00 -0700
Subject: [PATCH] mathlib: add PointsAlongLine

---
 common/mathlib.cc         | 17 +++++++++++++++++
 include/common/mathlib.hh |  2 ++
 light/test_light.cc       |  7 +++++++
 3 files changed, 26 insertions(+)

diff --git a/common/mathlib.cc b/common/mathlib.cc
index 77dd6b45..c387b2c3 100644
--- a/common/mathlib.cc
+++ b/common/mathlib.cc
@@ -540,3 +540,20 @@ std::vector<glm::vec3> GLM_ShrinkPoly(const std::vector<glm::vec3> &poly, const
     
     return clipped;
 }
+
+std::vector<glm::vec3> PointsAlongLine(const glm::vec3 &start, const glm::vec3 &end, const float step)
+{
+    const vec3 linesegment = end - start;
+    const float len = length(linesegment);
+    if (len == 0)
+        return {};
+    
+    vector<vec3> result;
+    const vec3 dir = linesegment / len;
+    const int stepCount = static_cast<int>(len / step);
+    for (int i=0; i<=stepCount; i++) {
+        vec3 pt = start + (dir * (step * i));
+        result.push_back(pt);
+    }
+    return result;
+}
diff --git a/include/common/mathlib.hh b/include/common/mathlib.hh
index 9f773eb3..0c634a04 100644
--- a/include/common/mathlib.hh
+++ b/include/common/mathlib.hh
@@ -397,4 +397,6 @@ V bilinearInterpolate(const V &f00, const V &f10, const V &f01, const V &f11, co
     return fxy;
 }
 
+std::vector<glm::vec3> PointsAlongLine(const glm::vec3 &start, const glm::vec3 &end, const float step);
+
 #endif /* __COMMON_MATHLIB_H__ */
diff --git a/light/test_light.cc b/light/test_light.cc
index 6a62e8f5..ec2fef00 100644
--- a/light/test_light.cc
+++ b/light/test_light.cc
@@ -589,3 +589,10 @@ TEST(mathlib, bilinearWeightsAndCoords2) {
     EXPECT_EQ(vec2(2, 1.5), sum);
 }
 
+TEST(mathlib, pointsAlongLine) {
+    const auto res = PointsAlongLine(vec3(1,0,0), vec3(3.5, 0, 0), 1.5f);
+
+    ASSERT_EQ(2, res.size());
+    ASSERT_TRUE(pointsEqualEpsilon(vec3(1,0,0), res[0], POINT_EQUAL_EPSILON));
+    ASSERT_TRUE(pointsEqualEpsilon(vec3(2.5,0,0), res[1], POINT_EQUAL_EPSILON));
+}