Sprite Masking in SFML2

[Laurent]

Okay, this version prevents you from using a texture to cut out areas. It will remove the complete bounding box of the sprite, no matter what the texture contains (I guess due to the BlendNone thing).

Yep. Could probably also be solved with the right blending mode.

I'd like to try out the pixel shader one, but I have absolutely no clue how to write shaders.

Here is a shader that sets alpha = 0 for pixels equal to a predefined colorkey:

uniform sampler2D texture;
uniform vec4 colorkey;

void main()
{
    vec4 pixel = texture2D(texture, gl_TexCoord[0].xy);
    if (pixel == colorkey)
        pixel.a = 0;
    gl_FragColor = pixel;
}

sf::Shader shader;
shader.loadFromFile("colorkey.frag", sf::Shader::Fragment);
shader.setParameter("texture", sf::Shader::CurrentTexture);
shader.setParameter("colorkey", sf::Color(/* whatever (magenta) */));

...

window.draw(sf::Sprite(target.getTexture()), &shader);
 

[Dienes]

Just tested it and it works perfectly, thank you!

Much better and faster solution!

[ChonDee]

Wow, thanks very much, that's exactly what I wanted, I am definitely going to make good use of this!

Also thanks for the answers to my questions from both of you. 

[Vovosunt]

There's a simpler and more efficient solution to this problem. You can create holes in the render-texture by rendering stuff with alpha = 0 and blend mode set to BlendNone. This way there's no need for a custom pixel shader, transparency is directly and correctly written to the target.

#include <SFML/Graphics.hpp>

int main()
{
    sf::RenderWindow window(sf::VideoMode(800, 600), "SFML holes");
    window.setVerticalSyncEnabled(true);

    sf::RenderTexture target;
    if (!target.create(window.getSize().x, window.getSize().y))
        return -1;

    target.clear(sf::Color::White);
    target.display();

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

        if (sf::Mouse::isButtonPressed(sf::Mouse::Left))
        {
            sf::Vertex point(sf::Vector2f(sf::Mouse::getPosition(window)), sf::Color::Transparent);
            target.draw(&point, 1, sf::Points, sf::BlendNone);
            target.display();
        }

        window.clear();
        window.draw(sf::Sprite(target.getTexture()));
        window.display();
    }

    return 0;
}

What the... I asked about this a week or so ago and we both agreed that it didn't work O_O
BTW just wondering, why are the completely transparent sprites won't do the same thing?
VertexArrays set to Quads will thought, so it doesn't really matter, but nonetheless.

[Laurent]

What the... I asked about this a week or so ago and we both agreed that it didn't work O_O

No, remember what I said:

I need to clear a part of a renderTexture, but using transparent sprites/shapes won't work. They have got to have at least 1/255 opacity even with BlendMode set to BlendNone.

I changed this a few days ago, it should work with the latest revision of SFML 2.

BTW just wondering, why are the completely transparent sprites won't do the same thing?

Completely transparent sprites will work.

[Vovosunt]

Oh. Indeed they do

[Vovosunt]

I think the BlendMultiply BlendFunc is incorrect.
Why glBlendFunc(GL_DST_COLOR, GL_ZERO)?
It doesn't work with transparency.

[Vovosunt]

But I guess there's no real way to do it with Alpha.
Thought I think (GL_DST_COLOR, GL_ONE_MINUS_SRC_ALPHA) is a bit better.
Or maybe you could use the glBlendFuncSeparateEXT and add the alphas together or keeping only the destination alpha?
Seems logical.

Blendmodes are sometimes so hard to get you mind around 
Good for reference: http://www.andersriggelsen.dk/glblendfunc.php

[Laurent]

Or maybe you could use the glBlendFuncSeparateEXT and add the alphas together or keeping only the destination alpha?
Seems logical.

Hmm yes, sounds like a good idea. However I'd use glBlendFuncSeparateEXT to keep the source alpha.

[Vovosunt]

So, continuing on, if I'm gonna add some blendMode stuff to sfml, do I just insert it into the glCheck?
Does stuff like glBlendEquation also work?
And what is glCheck anyway? (couldn't really find anything on the net, but I guess it's something that checks gl states and sets them if they're not set...)

[Laurent]

Does stuff like glBlendEquation also work?

Yes.

And what is glCheck anyway? (couldn't really find anything on the net, but I guess it's something that checks gl states and sets them if they're not set...)

It prints a message if the GL function fails. Look at src/Graphics/GLCheck.cpp (it's a SFML function).

[Vovosunt]

It prints a message if the GL function fails. Look at src/Graphics/GLCheck.cpp (it's a SFML function).

I already did, but didn't quite get it it seems. So it's just an error catcher

Thanks for the quick answer, Laurent

[Vovosunt]

Ok everything works, except that GL_MIN equation sticks around, and everything renders with it...
Were should I reset the original GL_FUNC_ADD?

[Laurent]

Were should I reset the original GL_FUNC_ADD?

Everytime a blending mode is set that is not the MIN one (in applyBlendMode).

[vidjogamer]

Why doesnt this work:

Code: [Select]

sf::CircleShape circle(5,32);
circle.setPosition( sf::Mouse::getPosition(window).x, sf::Mouse::getPosition(window).y );
circle.setFillColor(sf::Color::Transparent);
target.draw(circle,sf::BlendNone);
target.display();

if this works:

Code: [Select]

sf::Vertex point(sf::Vector2f(sf::Mouse::getPosition(window)), sf::Color::Transparent);
target.draw(&point, 1, sf::Points, sf::BlendNone);
target.display();