mathlib: add PointsAlongLine

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;
+}

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__ */

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));
+}