Update J2D.cpp

Dramatically improve the speed of J2D::DrawCubicBezierCurve

src/renderer/OpenGL/J2D.cpp

@@ -826,23 +826,24 @@ void JGL::J2D::FillGradientTriangle(const Color4& a_color, const Color4& b_color
     glColor4fv(default_state.draw_color);
 }
 
-//TODO render all in once pass with GL_LINE_LOOP instead of separate lines.
 void JGL::J2D::DrawCubicBezierCurve(const Color4& color, const Vector2& controlA, const Vector2& pointA, const Vector2& pointB, const Vector2& controlB,
                                int subdivisions, float thickness) {
 
 
     Vector2 last = controlA;
     const Vector2& first = controlB;
-    for (int i = 0; i < subdivisions; ++i)
-    {
+
+    std::vector<Vector2> vertices(2 * subdivisions + 2);
+    for (int i = 0; i < subdivisions; ++i) {
         float alpha = (float) i / (float) subdivisions;
         Vector2 step = J3ML::Algorithm::Bezier(alpha, controlA, pointA, pointB, controlB);
-        DrawLine(color, last, step, thickness);
+        vertices[2 * i] = last;
+        vertices[2 * i + 1] = step;
         last = step;
     }
-
-    // Have to manually draw the last segment of the curve.
-    DrawLine(color, last, first, thickness);
+    vertices[2 * subdivisions] = last;
+    vertices[2 * subdivisions + 1] = first;
+    DrawLines(color, vertices.data(), vertices.size(), thickness);
 }
 
 void JGL::J2D::OutlinePolygon(const Color4& color, const Vector2* points, int points_size, float thickness) {