Problem with Blending?

[Austech]

Since I found out about blending in sfml. I decided to put it to the test with a little program that represents a flashlight.

Code: [Select]

while(1)
{
while(window.GetEvent(event))
{
if(event.Type == sf::Event::Closed)
{
window.Close();
}
}
window.Clear();

sf::Shape hidden = sf::Shape::Rectangle(0,0,100,100,sf::Color(255,0,0,0));
hidden.SetBlendMode(sf::Blend::Add);

sf::Shape circ = sf::Shape::Circle(window.GetInput().GetMouseX(),window.GetInput().GetMouseY(), 40,sf::Color(255,255,255,100));
window.Draw(circ);
window.Draw(hidden);
window.Display();
}

I thought the Blend Mode, Add, would add the alpha of the hidden box, (0), to the alpha of the circle, (100). Wouldn't it?

[Laurent]

A blend operation is between a source (the shape, the hidden box) and a target (the window), not between two separate sources. So, each call to Draw adds the alpha of the corresponding shape to the alpha of the window, which is 255.

And I must say that I have no idea about what effect you're trying to achieve

[Austech]

A blend operation is between a source (the shape, the hidden box) and a target (the window), not between two separate sources. So, each call to Draw adds the alpha of the corresponding shape to the alpha of the window, which is 255.

And I must say that I have no idea about what effect you're trying to achieve

Oh my bad. What I was trying to simulate was when the circle was over the shape (hidden), it would show the part of the shape in which the circle is over.