How to draw multiple objects of the same shape in SFML using VertexArray?

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Summary

The problem at hand is drawing multiple objects of the same shape in SFML using VertexArray. The provided code snippet successfully draws a single rectangle, but the goal is to replicate this shape multiple times on the screen for collision testing purposes. Key takeaways include understanding how to utilize VertexArray efficiently for multiple shapes and applying collision detection techniques.

Root Cause

The root cause of the issue lies in the misunderstanding of the SFML documentation examples, specifically the tile and particle examples, which are meant to illustrate how to draw multiple objects. The main causes include:

  • Lack of clarity on how to apply the concepts to custom shapes like rectangles.
  • Difficulty in adapting the examples for collision testing purposes.
  • Insufficient understanding of SFML’s drawing mechanisms and how to optimize them for multiple objects.

Why This Happens in Real Systems

In real-world applications, this issue arises due to:

  • Complexity of graphics rendering: Managing multiple objects on the screen can become complex, especially when dealing with custom shapes and collision detection.
  • Performance optimization: The need to optimize rendering for multiple objects to ensure smooth performance can lead to confusion, especially for developers new to SFML or graphics programming.
  • Limited documentation understanding: Sometimes, official documentation might not fully address the specific use case or might be too generic, leading to confusion among developers.

Real-World Impact

The impact of not being able to draw multiple objects of the same shape includes:

  • Delayed project timelines: Spending more time than anticipated on figuring out how to render multiple custom shapes can delay project completion.
  • Performance issues: Incorrectly rendering multiple objects can lead to performance issues, such as lag or crashes, affecting the overall user experience.
  • Increased development cost: The additional time and resources spent on resolving these issues can increase the development cost.

Example or Code

#include 

int main() {
    sf::RenderWindow window(sf::VideoMode({800, 800}), "Test Window");
    sf::VertexArray rectangle(sf::PrimitiveType::TriangleStrip, 4);

    // Define the rectangle's vertices
    rectangle[0].position = sf::Vector2f(100.f, 100.f);
    rectangle[1].position = sf::Vector2f(100.f, 110.f);
    rectangle[2].position = sf::Vector2f(120.f, 100.f);
    rectangle[3].position = sf::Vector2f(120.f, 110.f);

    // Create multiple rectangles
    for (int i = 0; i < 10; i++) {
        for (int j = 0; j < 10; j++) {
            sf::VertexArray rect = rectangle;
            rect[0].position = sf::Vector2f(100.f + i * 20.f, 100.f + j * 20.f);
            rect[1].position = sf::Vector2f(100.f + i * 20.f, 110.f + j * 20.f);
            rect[2].position = sf::Vector2f(120.f + i * 20.f, 100.f + j * 20.f);
            rect[3].position = sf::Vector2f(120.f + i * 20.f, 110.f + j * 20.f);

            window.draw(rect);
        }
    }

    while (window.isOpen()) {
        sf::Event event;
        while (window.pollEvent(event)) {
            if (event.type == sf::Event::Closed)
                window.close();
        }

        window.clear();
        // Draw all rectangles here
        for (int i = 0; i < 10; i++) {
            for (int j = 0; j < 10; j++) {
                sf::VertexArray rect = rectangle;
                rect[0].position = sf::Vector2f(100.f + i * 20.f, 100.f + j * 20.f);
                rect[1].position = sf::Vector2f(100.f + i * 20.f, 110.f + j * 20.f);
                rect[2].position = sf::Vector2f(120.f + i * 20.f, 100.f + j * 20.f);
                rect[3].position = sf::Vector2f(120.f + i * 20.f, 110.f + j * 20.f);

                window.draw(rect);
            }
        }
        window.display();
    }

    return 0;
}

How Senior Engineers Fix It

Senior engineers fix this issue by:

  • Breaking down the problem: Understanding the requirement to draw multiple objects and identifying the most efficient way to achieve this using SFML.
  • Optimizing rendering: Ensuring that the rendering of multiple objects is optimized for performance to avoid lag or other issues.
  • Applying best practices: Following SFML best practices for drawing multiple objects, such as using vertex arrays efficiently and minimizing the number of draw calls.

Why Juniors Miss It

Juniors might miss the solution due to:

  • Lack of experience: Limited experience with SFML or graphics programming can make it difficult to understand how to efficiently draw multiple objects.
  • Insufficient understanding of SFML concepts: Not fully grasping SFML’s drawing mechanisms and how to apply them to custom shapes can lead to confusion.
  • Overlooking optimization: Failing to consider performance optimization when drawing multiple objects, which can lead to issues down the line.