Getting a Pixel to print to the screen using SFML & C++ - c++

Question

My main goal is to convert a bunch of pairs of numbers from a text file (numbers.txt) and assign each of these numbers as pixel coordinates. Then I need to print a pixel at each of those coordinates that will eventually form a picture of the United States composed of only single pixels.
Right now, what I'm doing is just trying to get any pixel of any color to print to the screen using SFML. Maybe if I can get that far I can somehow take the numbers stored in numbers.txt and convert them to coordinates with a pixel at each one.
Here's my code so far...
#include <iostream>
#include <fstream> // the fstream class
#include <SFML/Graphics.hpp>
#include <string> // will help to use strings
using namespace std;
int main()
{
string line;
int width, height;
fstream myFile;
myFile.open("resources/numbers.txt");
if (myFile)
{
cout << "This file is opened\n";
}
else
return EXIT_FAILURE;
cout << "Enter 2 integer values";
cin >> width >> height;
// Print a black window to the screen
sf::RenderWindow window(sf::VideoMode(width, height), "MAP");
sf::Texture texture;
sf::Sprite sprite;
sprite.setTexture(texture);
while (window.isOpen())
{
sf::Event event;
while (window.pollEvent(event))
{
switch (event.type)
{
case sf::Event::Closed:
window.close();
break;
}
}
window.clear();
//window.draw(sprite);
//*************DRAW THE SPRITE HERE****************
// create a new vertex
sf::Vertex vertex;
// set its position
vertex.position = sf::Vector2f(10.f, 50.f);
// set its color
vertex.color = sf::Color::Red;
// set its texture coordinates
vertex.texCoords = sf::Vector2f(100.f, 100.f);
sf::VertexArray pixel(sf::Points);
window.draw(pixel);
//display window
window.display();
}
return 0;
}
This does compile fine. But only displays a black screen to the user. I need to somehow get a pixel on that black screen. I am very new to SFML and C++ and looked up on the SFML mainpage about points and pixels but only got this far. Can any of you guys help? It's super appreciated!
All the best.

Answer 1

there are several approaches in SFML to draw a single pixel on the screen. The first one is what you are trying to do with sf::VertexArray.
In my opinion the simpler and more intuitive is approach with sf::RectangleShape where you can create rectangle with 1x1 size and this one I am going to present you.
Firstly, we can add helpful function which will create "pixel" at given position and color.
sf::RectangleShape addPixel(sf::Vector2f position, sf::Uint8 red, sf::Uint8 green, sf::Uint8 blue)
{
sf::RectangleShape pixel;
pixel.setSize({ 1.f, 1.f });
pixel.setFillColor({ red, green, blue });
pixel.setPosition(position);
return pixel;
}
That function will return sf::RectangleShape with the color created from RGBs values passed as arguments to that function.
But you have to store these pixels somewhere.
So let's create window, and some container to hold our pixels, e.g. std::vector<sf::RectangleShape>
and add to it some pixels:
sf::RenderWindow window(sf::VideoMode(800, 600), "SFML window");
std::vector<sf::RectangleShape> pixels;
pixels.push_back(addPixel({ 100, 100 }, 255, 0, 0));
pixels.push_back(addPixel({ 101, 100 }, 255, 255, 0));
pixels.push_back(addPixel({ 102, 100 }, 0, 0, 0));
pixels.push_back(addPixel({ 103, 100 }, 255, 0, 255));
Finally you create main loop where you draw all pixels in each iteration.
while (window.isOpen())
{
window.clear();
for (const auto& pixel : pixels)
{
window.draw(pixel);
}
window.display();
}
Make sure you add more pixels before trying to display it. On high resolution screen single pixels could be invisible.
EDIT: You code also works but you forgot to add sf::Vertex to sf::VertexArray.
All you should do is:
sf::Vertex vertex1;
vertex1.position = sf::Vector2f(10.f, 50.f);
vertex1.color = sf::Color::Red;
sf::VertexArray pixel;
pixel.append(vertex1); // That's what you forgot.
window.draw(pixel);
As above, with this approach also add more sf::Vertex next to each other, otherwise you may not notice single pixel on the screen.
Hope it helps!