Draw loop and Lua (Luabridge) - c++

Question

I'm currently stuck on some issue and don't know how to fix it.
I started working on a simple 2D engine using SFML for rendering stuff and Lua as my scripting language.
The engine starts with a splash screen first before Lua code is loaded ...
My problem is I don't know how to write a "good" draw loop for my Lua objects.
Maybe you'll understand when we take a look on my code:
Main.cpp:
...
int draw_stuff()
{
sf::RenderWindow window(sf::VideoMode(640, 480), TITLE);
while (window.isOpen()) {
sf::Event event;
while (window.pollEvent(event))
{
if (event.type == sf::Event::Closed)
window.close();
}
window.clear();
if (!success) {
window.draw(sp_splash_screen);
}
if (clock.getElapsedTime().asSeconds() > 2) {
for (static bool first = true; first; first = false)
{
std::thread thr(&lua_module);
thr.detach();
success = true;
}
}
for (sf::CircleShape obj : CircleDrawList) {
window.draw(obj);
//window.draw(CircleDrawList.front());
}
}
return 0;
}
My CircleShape wrapper class for Lua:
/////shapes.h
extern std::list<sf::CircleShape> CircleDrawList;
class Circle
{
public:
Circle();
...
void draw();
private:
sf::CircleShape circleShape;
protected:
//~Circle();();
};
/////shapes.cpp
std::list<sf::CircleShape> CircleDrawList;
...
void Circle::draw()
{
//std::cout << "DRAW IN LIST" << std::endl;
CircleDrawList.push_front(circleShape);
//if (drawableList.size() == 4)
//drawableList.pop_front();
}
...
int luaopen_shapes(lua_State *L)
{
luabridge::getGlobalNamespace(L)
.beginClass<Circle>("Circle")
.addConstructor <void(*) (void)>()
... "other stuff to register" ...
.addFunction("draw", &Circle::draw)
.endClass();
return 1;
}
and finally (if needed) my lua script:
local ball = Circle()
ball:setColor(255,0,0,255)
while true do
ball:draw()
end
Result when the Lua Circle is moving by increasing one of the Vector2 values:
Hope you can help and I described it good :x
Thanks :)
-- Updated code in main.cpp

Answer 1

I'm not sure what is happening, but I see some problems in the code.
First: you don't remove "old" CircleShapes from CircleDrawList.
In the function Circle::draw() you are pushing object to the front of the list with CircleDrawList.push_front(circleShape); but you never remove anything from it. Using CircleDrawList.front() gives you access to the first element but you have to use method pop_front() to remove it.
Second thing. Look at the code:
//iterating through whole list with range-for:
for (sf::CircleShape obj : CircleDrawList)
{
//why do you use CircleDrawList.front()?
//You should probably use obj here!
window.draw(CircleDrawList.front());
}
As for now this code draws first element of the list n times where n is the length of the CircleDrawList. Do you really want to do this?
Moreover you are drawing splash every frame. If you wish to display splash only at the beginning, then the line window.draw(splash_screen); // splash screen before Lua script is loaded should probably be in some sort of conditional instruction.
I don't know what is between drawing splash_screen and drawing circles. It could have some impact on what we see on the screen.
And one more thing: it is strongly recommended to avoid using global variables. CircleDrawList is a global variable and my advice would be to put it at least in some namespace, or even better to enclose it in some class.