3D Games Rendering - Érico de Morais Nunes

May 23, 2009 Tchelinux 2009 1

Érico de Morais Nunes - [email protected]

Universidade Federal do Pampa

3D Games Rendering


Summary● About me

● This talk is not about

● Introduction

● Definitions

● OpenGL

● 3D Pipeline Overview

● 3D Rendering Topics

● Shaders and the “future” of 3D development

● Conclusion


● About me


● Introduction

● Definitions

● OpenGL




● Conclusion


About Me

● I am a Computer Engineering student.● 3D Rendering is not my main research

area, though I have used it in projects.● I have been into computer graphics for

around a year and a half.● I have not produced any commercial

games.● I am a (casual) gamer. :)


Summary● About me


● Introduction

● Definitions

● OpenGL




● Conclusion


This talk is not about

● Unfortunately, this talk is not aimed at...● NVIDIA A is better than ATI B.● Card X runs game Y.● How to code a game.● How to get past level N of game X.

● It is aimed at rendering!


● About me


● Introduction

● Definitions

● OpenGL




● Conclusion


Introduction

● Games nowadays look just damn real!● And in real time!


Introduction

● How do they do it?


Introduction

● We could also go a bit back...● How did they do it, back at the days?

Doom, 1993

System req:

80386 class CPU

(12~40 MHz)

4 MB RAM


Introduction

● In this talk, we shall see the science behind graphics.


● About me


● Introduction

● Definitions

● OpenGL




● Conclusion


Definitions

● Rendering – Process of creating the 3D image you see on the screen.

● Modeling – Process of generating models to render. For example, designing the characters' models in software like Blender.


Definitions

● Pixel – One “dot of color” in your screen.● Vertex – It could be a coordinate in the 3D

space. Like the ones in math.● Fragment – It is all the data needed to generate

a pixel. Depth, color, texture coordinate... Do not confuse it with the pixel itself – you can have many fragments in a pixel space.

● Texture – Name given to an image attached to some geometry in your scene.


Definitions

● OpenGL – The cross platform standard API for 3D graphics.

● API – Application Programming Interface. Used to provide an interface to some device.

● GPU – Graphics Processing Unit. Same as the “Graphics card”.

→ These definitions only aim to make quick explanations so that we can go further without major problems :)


● About me


● Introduction

● Definitions

● OpenGL




● Conclusion


OpenGL

● “The Industry's Foundation for High Performance Graphics.”

● “From games to virtual reality, mobile phones to supercomputers.”


OpenGL

OpenGL (Open Graphics Library) is a standard specification defining a cross-platform API for writing applications that produce 2D and 3D computer graphics.


OpenGL

● Some considerations:● It is a rendering API!● OpenGL is not open source.

(There is an open source implementation similar to it, Mesa).

● Maintained by the OpenGl ARB. ● OpenGL is the standard API used in Linux 3D

rendering software.


OpenGL

● As for this talk, we are mainly interested in understanding the OpenGL Rendering Pipeline.


● About me


● Introduction

● Definitions

● OpenGL




● Conclusion


3D Pipeline

● Do not be scared!● Pipeline: “a chain of data-processing

stages”.

Ok. I want to draw a line and a triangle. What do I need to provide and what steps are performed for it to be rendered?


3D Pipeline

http://www.lighthouse3d.com/opengl/glsl/index.php?pipeline


3D Pipeline - Vertex

● Vertices are user defined (or loaded from a model). They define your geometry.

● Note that each one has an associated color.

● At games, generally, a texture is provided instead.


3D Pipeline - Transformation

● Transformation is related to changing the vertex position.

● It is important – when something needs to move/animate, its vertices need to be transformed!

● Transformation is defined by the user, performed by the pipeline.


3D Pipeline – Assembly

● So far, we only have

vertices, coordinates.

● Besides vertices, we have also provided the information on how to connect them.


3D Pipeline - Rasterization

● Very important step!

● Your eyes trick you:

Your screen is 2D.

● Rasterization: converting from the 3D space into the “plane” screen space. Fragments.


3D Pipeline - Interpolation

● Finally, we perform interpolation between the fragments.

● That is: calculate the color on each pixel, based on the colors at the vertices.


3D Pipeline

● That's it.

●

● You now have base knowledge on how it goes for rendering geometry, in a few simple steps!


3D Pipeline

● To finish with it, here is a more complete (and complex) pipeline model:


● About me


● Introduction

● Definitions

● OpenGL




● Conclusion


3D Rendering Topics

● Now, let's touch at some interesting topics in 3D rendering that are vastly employed in games, such as:● Depth Testing● Space Partitioning● Ray Tracing● Texture Mapping● Modeling


3D Rendering Topics

● Objects can be hidden behind other objects.

● OpenGL does not do standard check to figure out which object should be in front and which should be hidden.

● You need to find a way to do it yourself. ● What if you don't?


3D Rendering Topics

● Well, this might happen:


3D Rendering Topics

● One way to do it is called Depth Testing.● Each fragment has a depth associated to

it, resulting from rasterization● Depth testing performs per fragment

check to identify which fragment is closer to the viewer.


3D Rendering Topics

● Depth testing works!

● However, you shouldn't rely on that only.● For large sceneries, checking every

fragment could be very slow. :(


3D Rendering Topics

● Ok, think on this:

Could you ever possibly see anything inside the building from here?


3D Rendering Topics

● Probably not.● In this case, wouldn't it be wise to discard

everything inside it, ahead of time?


3D Rendering Topics

● We can extend this even more:

● We can't see behind that door. We can discard that part of the map.


3D Rendering Topics

● This is a kind of Space Partitioning.● It consists in knowing which parts of the

map aren't visible and loading them as they appear.


3D Rendering Topics

Doom was only possible back then because of Space Partitioning!


3D Rendering Topics

● Out of hidden surfaces, another cool feature is Ray Tracing.

● Ray Tracing is a vector based model which is used to, for example, model light rays and achieve high lighting and shadows realism.


3D Rendering Topics


3D Rendering Topics

● Texture Mapping: consists of adding pictures to geometry to simulate extra detail.

● For long, games have been relying in texturing to achieve some degree of realism.


3D Rendering Topics

● Detailed scenery?!

● Textures are a cheap way to add realism.


3D Rendering Topics

● Modeling: how can models made in 3D modelers be added to the OpenGL Pipeline?


3D Rendering Topics

● That's no OpenGL business.● Your 3D modeler probably supports

exporting to many different model formats.

● To load it into your game, you load and parse the file yourself, and pass OpenGL the raw ready data :)


● About me


● Introduction

● Definitions

● OpenGL




● Conclusion


Shaders and the “future”

● So far, we have only seen a hard defined 3D pipeline, with well defined functions.

● While this could be enough for many tasks, in order to achieve realism, you would need more flexibility.



● A Shader is a piece of code which is used primarily to calculate rendering effects on graphics hardware with a high degree of flexibility.

● GLSL, HLSL, ● In your shader, you can do many cool

things like...



Cell Shading

Per Pixel Lighting



● OpenGL currently supports Vertex Shaders and Pixel Shaders.

● Let's take a look on the new pipeline, with shaders in!



● Some sources say that Shaders are the future of 3D graphics.

● It is not the future. It is the current state of the art.

● Almost everything came down to shaders.

… everything else is on its way to become a shader.


● About me


● Introduction

● Definitions

● OpenGL




● Conclusion


Conclusion

● The pipeline is a very important part of graphics rendering.

● Understanding the pipeline is on way to understand what goes on the GPU.

● Figuring out data to be discarded plays major part on performance and detailing level.

● Current games rely heavily in shaders and texturing for highly realistic graphics.


Just in case...

● Good reference books:● The OpenGL Superbible 4th Edition● The OpenGL Programming Guide (The Redbook)● OpenGL Shading Language (Orange Book)

● Good web resources for starters:● http://www.lighthouse3d.com● http://nehe.gamedev.net● http://www.videotutorialsrock.com ● http://www.opengl.org


Thank you!

Érico de Morais Nunes

[email protected]

3D Games Rendering - Érico de Morais Nunes

Technology

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