message: Internals: ImLerp() helper for ImVec4
diff: @@ -147,6 +147,7 @@ static inline int ImLerp(int a, int b, float t)
  static inline float ImLerp(float a, float b, float t) { return a + (b - a) * t; }
  static inline ImVec2 ImLerp(const ImVec2& a, const ImVec2& b, float t) { return ImVec2(a.x + (b.x - a.x) * t, a.y + (b.y - a.y) * t); }
  static inline ImVec2 ImLerp(const ImVec2& a, const ImVec2& b, const ImVec2& t) { return ImVec2(a.x + (b.x - a.x) * t.x, a.y + (b.y - a.y) * t.y); }
  +static inline ImVec4 ImLerp(const ImVec4& a, const ImVec4& b, float t) { return ImVec4(a.x + (b.x - a.x) * t, a.y + (b.y - a.y) * t, a.z + (b.z - a.z) * t, a.w + (b.w - a.w) * t); }
  static inline float ImLengthSqr(const ImVec2& lhs) { return lhs.x*lhs.x + lhs.y*lhs.y; }
  static inline float ImLengthSqr(const ImVec4& lhs) { return lhs.x*lhs.x + lhs.y*lhs.y + lhs.z*lhs.z + lhs.w*lhs.w; }
  static inline float ImInvLength(const ImVec2& lhs, float fail_value) { float d = lhs.x*lhs.x + lhs.y*lhs.y; if (d > 0.0f) return 1.0f / sqrtf(d); return fail_value; }
  