ICG 2010 Oral Presentation

8/2/2019 ICG 2010 Oral Presentation

1/27

Screen Space AmbientOcclusion(SSAO)

B97902099

B97902045 B98902077


2/27

Why we need SSAO?

We have learned that a shadow is generated when the rayintersects a surface before it meets a light source.


3/27

What if we are in the sunlight shadowalready?

In the real world


4/27


5/27


6/27

If we are already in theshadow,we need somethingelse...


7/27

Ambient Occlusion

Ambient OcclusionAmbient = (Ambient Light)

Occlusion = , ,

Occluded

Ambient Light


8/27

What's AO


9/27

What's AO


10/27

What's AO


11/27


12/27


13/27

AO Equation

V(p,p') is the visibility function from p' to p,

Recall Rendering Equation:

Since ambient is undirectional and uniform.

http://www.codecogs.com/latex/eqneditor.php


14/27

AO Equation

integrating the visibility function over the hemisphere with respect to projected solid angle


15/27

SSAO

SSAO = Screen Space Ambient OcclusionAOScreen Space


16/27

SSAO

Depth Buffer

==>


17/27

SSAO

poisson-disk

sample


18/27

SSAOAO-factor


19/27

SSAO

, AO mapAmbient

+

=

+...


20/27

THE END

Thanks for Attention


21/27

Problem & Goal

1. 2.


22/27

Algorithm

A. Read depth map as a height map

B. For each pixel (denotes p0), sample neighbor pixels todetermine how much p0 will be occluded.

(It can be executed in Fragment Shader)

C. Write the p0 to the output buffer. The output buffer is calledAO-map.


23/27

Algorithm

Input: DepthBuffer as Texture2DGeometry: A QuadOutput: AO-Map composed of the results of ssao()

vec4 ssao(Texture2D depthMap, vec2 center){sample neighbors of the centercalculate how much the center will be occluded.AO-factor = some-function( some parameters )

return AO-factor}


24/27

With OpenGL

First Pass:Draw Models to G-Buffer (Depth & Normals).

Second Pass:

Use G-Buffer as textures, post-process it with SSAO function.Output its result to AO-map buffer.

Final Pass:Draw Models to Display Buffer, with the calculated AO-map

buffer as a special texture.


25/27

Algorithm (OpenGL)

1st-Pass:

Draw Models/Scene to Depth Buffer


26/27

Algorithm (OpenGL)

2nd-Pass:Use SSAO shader,Draw a Full-screen Quad with Depth Buffer as Texture


27/27

AO Equation

Recall Rendering Equation

Documents

ICG 2010 Oral Presentation