light: add GLM_ProjectPointOntoPlane

common/mathlib.cc

@@ -400,6 +400,14 @@ float GLM_DistAbovePlane(const glm::vec4 &plane, const glm::vec3 &point)
     return dot(vec3(plane), point) - plane.w;
 }
 
+glm::vec3 GLM_ProjectPointOntoPlane(const glm::vec4 &plane, const glm::vec3 &point)
+{
+    float dist = GLM_DistAbovePlane(plane, point);
+    vec3 move = -dist * vec3(plane);
+    return point + move;
+}
+
+
 glm::vec3 GLM_PolyCentroid(const std::vector<glm::vec3> &points)
 {
     Q_assert(points.size() >= 3);

include/common/mathlib.hh

@@ -329,6 +329,7 @@ float GLM_EdgePlanes_PointInsideDist(const std::vector<glm::vec4> &edgeplanes, c
 glm::vec3 GLM_TriangleCentroid(const glm::vec3 &v0, const glm::vec3 &v1, const glm::vec3 &v2);
 float GLM_TriangleArea(const glm::vec3 &v0, const glm::vec3 &v1, const glm::vec3 &v2);
 float GLM_DistAbovePlane(const glm::vec4 &plane, const glm::vec3 &point);
+glm::vec3 GLM_ProjectPointOntoPlane(const glm::vec4 &plane, const glm::vec3 &point);
 glm::vec3 GLM_PolyCentroid(const std::vector<glm::vec3> &points);
 glm::vec4 GLM_PolyPlane(const std::vector<glm::vec3> &points);
 /// Returns the index of the polygon edge, and the closest point on that edge, to the given point

light/test_light.cc

@@ -402,6 +402,22 @@ TEST(mathlib, BarycentricRandom) {
     }
 }
 
+TEST(mathlib, DistAbovePlane) {
+    vec4 plane(0, 0, 1, 10);
+    vec3 point(100, 100, 100);
+    EXPECT_FLOAT_EQ(90, GLM_DistAbovePlane(plane, point));
+}
+
+TEST(mathlib, ProjectPointOntoPlane) {
+    vec4 plane(0, 0, 1, 10);
+    vec3 point(100, 100, 100);
+    
+    vec3 projected = GLM_ProjectPointOntoPlane(plane, point);
+    EXPECT_FLOAT_EQ(100, projected.x);
+    EXPECT_FLOAT_EQ(100, projected.y);
+    EXPECT_FLOAT_EQ(10, projected.z);
+}
+
 TEST(mathlib, InterpolateNormals) {
     // This test relies on the way GLM_InterpolateNormal is implemented