Do I really have to use std::vector<sf::CircleShape> ?

[Sakman]

Hello! Lets say I have collection of circles that I want to draw. They are identical in color, outline etc. Like shown in the picture above.

Let's say I store the positions and radiuses in vectors. I don't want to store every sf::CircleShape individually since that takes too much memory and makes the program slow.

Is there a way to make a single sf::CircleShape and use (tranform?) something to move and scale the circle with the vectors mentioned above? And is there a way to draw them with a single RenderTarget::draw() like with sf::VertexArray?

Responses are greatly appreciated.

[tomvidm]

You can make a vector std::vector<sf::Transformable>. Instead of iterating through a vector of circle shapes, iterate through the transforms. For each transform T, you call draw on the circle shape, pass a sf::RenderStates with T.getTransform() as the transform parameter. (Look at the declaration of sf::RenderStates structure)

This way, the vertices defining the circle itself does not change. The CircleShape itself is logically in the same place all the time, but the vertices are transformed and sent for rendering in turns.

[Hapax]

See my response to your duplicate post.

(click to show/hide)

Hello!

Hello!

I don't want to store every sf::CircleShape individually since that takes too much memory and makes the program slow.

How much memory do you think they take? Storing lots of circles shouldn't be slowing down your program. However, drawing lots of them may do that.

Is there a way to make a single sf::CircleShape and use (tranform?) something to move and scale the circle with the vectors mentioned above?

Yes, this is possible. You can create a single sf::CircleShape and modify it between each draw; this avoid the storage (but you still need to store where they are going to be somewhere) but makes the code messy (separating updating and drawing is a common 'tidy' approach).

And is there a way to draw them with a single RenderTarget::draw() like with sf::VertexArray?

sf::CircleShapes? No.
Two options that I can think of:

• If the circles don't move (at all or maybe don't move much), draw them all to a single render texture and then you only need a single draw call to draw that render texture,
• Create a vertex array and add the multiple circles to that vertex array; note that you will need to calculate the positions of all the points of each circle (you would probably use sf::Triangles for this)

[Sakman]

Thank you for your response!

I'm a bit confused. So what I need to do is make an empty texture and draw the circles on it?

Could you link a tutorial or an example, please. Thank you.

[verdog]

I'd probably wrap the group of circles into a class/struct:

struct CirclePosition {
  sf::Vector2f position;
  float radius;
}

struct CircleGroup {
  mutable sf::CircleShape base; // mutable so its radius can be changed within the draw function
  std::vector<CirclePosition> positions; // filled with a CirclePosition for each sf::CircleShape

  void draw(sf::RenderTarget& target, sf::RenderStates states) const {
    for (CirclePosition &cPosition : positions) {
      // apply the radius
      base.setRadius(cPosition.radius);

      // move the circle
      sf::Transform circleTransform;
      transform.translate(cPosition.position);
      states.transform = circleTransform;
      target.draw(base, states);
    }
  }
}
 

Pretty sloppy solution, and it might give you issues when you try to compile it (wrote it quickly at work  ), but maybe this can give you an idea to get started?

[Hapax]

I'm a bit confused. So what I need to do is make an empty texture and draw the circles on it?

Could you link a tutorial or an example, please. Thank you.

Again, if your circles do not move, yes, you can draw them to a kind of texture and then draw that texture in one draw call. However, if your circles are moving/changing, you'll still need at least as many draw calls (to draw them to the texture).

Basically, set up an sf::RenderTexture to match the window size and draw the circles to that in the same way you draw to a window (and prepare the sprite that draws the render texture):

std::vector<sf::CircleShape> circles;
sf::RenderTexture renderTexture;
// set up render texture and circles
renderTexture.clear();
for (auto& circle : circles)
    renderTexture.draw(circle);
renderTexture.display();
sf::Sprite renderSprite(renderTexture.getTexture());

This can be done before the main loop since they are not changing.
Also, you no longer need the vector of circle shapes...

Then, in the main loop where you are drawing to a window, just draw the render sprite:

while (window.isOpen())
{
    // event loop
    // updates
    window.clear();
    window.draw(renderSprite);
    window.display();
}