createMaskFromColor not working when updating image to texture

[zeno15]

I have a background texture that i move around using a view, and I want to add a few circles to it but without the background, so I am using image.createMaskFromColor(sf::Color::White), as the background is white, and then calling texture.update(image, ycoord, xcoord), the texture is updated, but the white background has been turned black, I was wondering if anyone knew the cause of this, the solution or maybe and alternative way to accomplish the same thing,
cheers.

[Laurent]

Do you set a specific blend mode when you draw the texture?

[zeno15]

No all the default values are used, I load the texture from a file (.png) and load it to a sprite, then draw the sprite, then i update the texture with the new images.

[Laurent]

Could you write a small example that reproduces the problem?

[zeno15]

#include <iostream>
#include <SFML/System.hpp>
#include <SFML/Window.hpp>
#include <SFML/Graphics.hpp>

int main() {

        sf::RenderWindow *window = new sf::RenderWindow(sf::VideoMode(800, 600), "My window");
       
        sf::Texture *backgroundtexture = new sf::Texture();
        backgroundtexture->loadFromFile("background.png");

        sf::Sprite *backgroundsprite = new sf::Sprite();
        backgroundsprite->setTexture(*backgroundtexture);

        sf::Image ball;
        ball.loadFromFile("ball.png");
        ball.createMaskFromColor(sf::Color::White);

        backgroundtexture->update(ball, 100, 100);




        while (window->isOpen()) {
                sf::Event event;
                while (window->pollEvent(event)) {
                        // check the type of the event...
                        switch (event.type) {
                                // window closed
                                case sf::Event::Closed:
                                        window->close();
                                        break;
                               
                                // we don't process other types of events
                                default:
                                        break;
                         }
                }

                window->clear();
                window->draw(*backgroundsprite);
                window->display();

        }

}
 

For me run on windows 7 using visual studio 2010 this creates the green background and the ball is updated onto the texture and the white background is turned black.



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[Laurent]

The black that you see is the background color (window->clear()). The area outside the circle is transparent, and when you update the texture this area remains transparent. So you see what's behind.

If you want to avoid that, you should draw to a sf::RenderTexture so that the alpha channel is interpreted when you copy the circle to the texture.

PS: why do you allocate every single object dynamically (without releasing them at the end)??

[zeno15]

Ah thank you

I'm allocating them dynamically because that's what I'm doing in a larger project and just didn't release them in this smaller example

[Laurent]

I'm allocating them dynamically because that's what I'm doing in a larger project

That's a really bad habit

[Nexus]

I'm allocating them dynamically because that's what I'm doing in a larger project and just didn't release them in this smaller example

Enter modern C++.

[masskiller]

I'm allocating them dynamically because that's what I'm doing in a larger project and just didn't release them in this smaller example

Then write a "TextureHolder" class that uses an STL container for the textures you are going to use. That's the best way to handle it if your project is going to go big. Be wary of std::vector though, it can be used for textures alright if you have a set amount of textures that won't change. If that won't happen in your case then use any other container.