Curve:getTangent;

src/api/types/curve.c

@@ -12,6 +12,17 @@ int l_lovrCurveEvaluate(lua_State* L) {
   return 3;
 }
 
+int l_lovrCurveGetTangent(lua_State* L) {
+  Curve* curve = luax_checktype(L, 1, Curve);
+  float t = luaL_checknumber(L, 2);
+  float point[3];
+  lovrCurveGetTangent(curve, t, point);
+  lua_pushnumber(L, point[0]);
+  lua_pushnumber(L, point[1]);
+  lua_pushnumber(L, point[2]);
+  return 3;
+}
+
 int l_lovrCurveRender(lua_State* L) {
   Curve* curve = luax_checktype(L, 1, Curve);
   int n = luaL_optinteger(L, 2, 32);
@@ -89,6 +100,7 @@ int l_lovrCurveRemovePoint(lua_State* L) {
 
 const luaL_Reg lovrCurve[] = {
   { "evaluate", l_lovrCurveEvaluate },
+  { "getTangent", l_lovrCurveGetTangent },
   { "render", l_lovrCurveRender },
   { "split", l_lovrCurveSplit },
   { "getPointCount", l_lovrCurveGetPointCount },

src/math/curve.c

@@ -59,6 +59,15 @@ void lovrCurveEvaluate(Curve* curve, float t, vec3 p) {
   evaluate(curve->points.data, curve->points.length / 3, t, p);
 }
 
+void lovrCurveGetTangent(Curve* curve, float t, vec3 p) {
+  float q[3];
+  int n = curve->points.length / 3;
+  evaluate(curve->points.data, n - 1, t, q);
+  evaluate(curve->points.data + 3, n - 1, t, p);
+  vec3_add(p, vec3_scale(q, -1));
+  vec3_normalize(p);
+}
+
 void lovrCurveRender(Curve* curve, float t1, float t2, vec3 points, int n) {
   lovrAssert(curve->points.length >= 6, "Need at least 2 points to render a Curve");
   lovrAssert(t1 >= 0 && t2 <= 1, "Curve render interval must be within [0, 1]");

src/math/curve.h

@@ -10,6 +10,7 @@ typedef struct {
 Curve* lovrCurveCreate(int sizeHint);
 void lovrCurveDestroy(void* ref);
 void lovrCurveEvaluate(Curve* curve, float t, vec3 point);
+void lovrCurveGetTangent(Curve* curve, float t, vec3 point);
 void lovrCurveRender(Curve* curve, float t1, float t2, vec3 points, int n);
 Curve* lovrCurveSplit(Curve* curve, float t1, float t2);
 int lovrCurveGetPointCount(Curve* curve);