CODEWITHSUNDEEP
javaopengllibgdxblending
A. Person
A. Person

Reputation: 131

What blending mode do I need to make images more transparent by drawing transparent images over them?

This picture explains what I am aiming for:

blending

Basically, I have a framebuffer and I want to make the contents of it more transparent by drawing a fullscreen shape over it. The color of this shape will play no role. I have tried this by using the following code:

// sr is ShapeRenderer
// fbo is FrameBufferObject

fbo.begin();

Gdx.gl.glClearColor(1, 0, 0, 1);
Gdx.gl.glClear(GL20.GL_COLOR_BUFFER_BIT);
Gdx.gl.glEnable(GL20.GL_BLEND);

sr.begin(ShapeRenderer.ShapeType.Filled);

Gdx.gl.glBlendFunc(GL20.GL_SRC_ALPHA, GL20.GL_ONE_MINUS_SRC_ALPHA);
sr.setColor(1, 1, 1, 1);
sr.circle(0, 0, 1);

Gdx.gl.glBlendFuncSeparate(GL20.GL_ZERO, GL20.GL_ONE, GL20.GL_ZERO, GL20.GL_ONE_MINUS_SRC_ALPHA);
sr.setColor(0, 0, 0, .5f);
sr.rect(0, 0, width, height);

sr.end();
fbo.end();

Instead of it working, I get a transparent black circle that keeps getting more transparent even though the buffer doesn't get refreshed. What I expected was a transparent white circle.

I expected this blending to take place:

R = Rsrc * 0 + Rdst * 1
G = Gsrc * 0 + Gdst * 1
B = Bsrc * 0 + Bdst * 1
A = Asrc * 0 + Adst * (1 - 0.5)

Does anyone know how to make this work properly?

Upvotes: 2

Views: 153

Answers (1)

Tenfour04
Tenfour04

Reputation: 93779

ShapeRenderer doesn't know you're changing the blendfunc, so you're drawing both the circle and the square with the second blendfunc that you set. You need to flush it in between.

Upvotes: 1

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