Use depth buffer in a Shader

advanced
#1

Hi !

I’d like to make a post processing effet that detects depth contrast to make a kind of cartoon effect.
My idea was to use an Fbo, take its depth layer and make a contour detection with a shader.
OF warns me that I should use ofFbo::Setting, the problem is that there is no documention in the OF web site. An other thing I was wondering, a depth buffer has only one layer (grey scales) so I was wondering who it should be dealt in my fragment shader.

Has any one any help or documentation about this ?

Thanks

Nico.

1 Like
openGL wrapper , vbo and shader location
#2

Hi Nico,

To use depth you have to use an ofFbo::Settings object.

ofFbo fbo;
ofFbo::Settings settings;
settings.width = width;
settings.height	= height;
settings.internalformat = GL_RGB; // or GL_RGBA?
settings.useDepth = true;
settings.depthStencilAsTexture = true;
fbo.allocate(settings);

Then use in the shader send it as a uniform texture:

shader.setUniformTexture("depth", fbo.getDepthTexture(), 0);

Although when I used the depth texture I didnt have access for some unknown reason, and had to paint it first on a new fbo in the color buffer, and then use this depthFbo.getTexture() to access the depth information:

depthFbo.begin();
ofClear(0);
ofSetColor(255);
fbo.getDepthTexture().draw(0,0);
depthFbo.end();

shader.setUniformTexture("depth", depthFbo.getTexture(), 0);

Tell me if you are able to use the getDepthTexture() directly.

To use it in the fragment shader, as it is a grayscale image, RGB channels contain the same information, so simply use depth.r to access the values.

Cheers

#3

@Hennio Thank you very much for this very clear and precise answer! I didn’t that the fbo could be allocated this way. Using depth buffers is a bit more tricky than I expected indeed.

I’ll try your methode during the week and I’ll give you feedback.

Cheers,

Nicolas

#4

also to be get anything in the depth texture you need to enable depth testing using ofEnableDepthTest() of glEnable(GL_DEPTH_TEST) otherwise the graphics card won’t write to the depth butffer

#5

It’s okay with this, the main problem was how to get the depth buffer to make post processing effect.
Juste a question, before writing the post, I tried to do

ofTexture myTexture = fbo.getDepthTexture();
shader.setUniformTexture("depth", myTexture, 0);

instead of

depthFbo.begin();
ofClear(0);
ofSetColor(255);
fbo.getDepthTexture().draw(0,0);
depthFbo.end();
shader.setUniformTexture("depth", depthFbo.getTexture(), 0);

I was wondering why It didn’t work