How to change the OpenGL blend mode directly?

spinvector

I'm looking to do a background invert filter for geometry (not post fx) and I've been told I can accomplish this by either:

a) multipass rendering, using a frame buffer and a shader.

b) change the openGL blend mode as suggested here.

Can someone tell me if b is possible using processing, and how? I know it's something to do with the opengl library wrapper in the graphics class but my attempts to use it have failed.

Thanks!

koogs

Which version of processing? (The answer changes with version)

spinvector

I'm running 2.2.1.

koogs

um, don't know. searching the forums i get the following code snippets to access opengl directly

here's what i used 3 years ago (probably 1.5.1 as that's what i usually use)

GL gl = ((PGraphicsOpenGL)g).gl;
gl.glEnable(GL.GL_BLEND);
gl.glBlendFunc(...);

here's something from 2 years ago:

http://forum.processing.org/one/topic/how-to-port-old-pgraphics-code-to-processing-2-alpha-additive-blending.html

PGraphicsOpenGL pgl = (PGraphicsOpenGL) g;
GL2 gl = pgl.beginPGL().gl.getGL2();
gl.glEnable(GL.GL_BLEND);
...

spinvector

Thankyou Koogs. Unfortunately none of those solutions work for me. it seems the gl object in the pgl doesn't exist for me (null ref)...