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Graphics / Can't set lower alpha value

« on: August 19, 2020, 07:25:19 pm »

Hello

I'm trying to erase parts of a render_target with a shader by setting the alpha to 0 but it's stay to 1 (255).

here is the fragment shader :

void main() {
     
   gl_FragColor = vec4(0.0, 0.0, 0.0,       0.0       );
}

and here the sfml code :

_renderTarget.clear(sf::Color(0,0,0,      255       ));
_window.clear(sf::Color(255,255,255,255);

_renderTarget.draw(_sprite,&erasingShader);// a 32x32 sprite at mouse location

_renderTarget.display();

sf::Sprite tempSprite(_renderTarget.getTexture());

_window.draw(tempSprite, sf::BlendAlpha);

_window.display();
 

Am I missing something ? it should displays a white square but its all black;