1. 3D Games Rendering
Érico de Morais Nunes - nunes.erico@gmail.com
Universidade Federal do Pampa
May 23, 2009 Tchelinux 2009 1

2. 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
May 23, 2009 Tchelinux 2009 2

3. ●
About me
●
This talk is not about
●
Introduction
●
Definitions
●
OpenGL
●
3D Pipeline Overview
●
3D Rendering Topics
●
Shaders and the “future” of 3D development
●
Conclusion
May 23, 2009 Tchelinux 2009 3

4. 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. :)
May 23, 2009 Tchelinux 2009 4

5. 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
May 23, 2009 Tchelinux 2009 5

6. This talk is not about
●
Unfortunately, this talk is not aimed at...
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NVIDIA A is better than ATI B.
●
Card X runs game Y.
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How to code a game.
●
How to get past level N of game X.
●
It is aimed at rendering!
May 23, 2009 Tchelinux 2009 6

7. ●
About me
●
This talk is not about
●
Introduction
●
Definitions
●
OpenGL
●
3D Pipeline Overview
●
3D Rendering Topics
●
Shaders and the “future” of 3D development
●
Conclusion
May 23, 2009 Tchelinux 2009 7

8. Introduction
●
Games nowadays look just damn real!
●
And in real time!
May 23, 2009 Tchelinux 2009 8

9. Introduction
●
How do they do it?
May 23, 2009 Tchelinux 2009 9

10. 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
May 23, 2009 Tchelinux 2009 10

11. Introduction
●
In this talk, we shall see the science
behind graphics.
May 23, 2009 Tchelinux 2009 11

12. ●
About me
●
This talk is not about
●
Introduction
●
Definitions
●
OpenGL
●
3D Pipeline Overview
●
3D Rendering Topics
●
Shaders and the “future” of 3D development
●
Conclusion
May 23, 2009 Tchelinux 2009 12

13. 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.
May 23, 2009 Tchelinux 2009 13

14. 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.
May 23, 2009 Tchelinux 2009 14

15. 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 :)
May 23, 2009 Tchelinux 2009 15

16. ●
About me
●
This talk is not about
●
Introduction
●
Definitions
●
OpenGL
●
3D Pipeline Overview
●
3D Rendering Topics
●
Shaders and the “future” of 3D development
●
Conclusion
May 23, 2009 Tchelinux 2009 16

17. OpenGL
●
“The Industry's Foundation for High
Performance Graphics.”
●
“From games to virtual reality, mobile
phones to supercomputers.”
May 23, 2009 Tchelinux 2009 17

18. OpenGL
OpenGL (Open Graphics Library) is a
standard specification defining a cross-
platform API for writing applications that
produce 2D and 3D computer graphics.
May 23, 2009 Tchelinux 2009 18

19. 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.
May 23, 2009 Tchelinux 2009 19

20. OpenGL
●
As for this talk, we are mainly interested
in understanding the OpenGL Rendering
Pipeline.
May 23, 2009 Tchelinux 2009 20

21. ●
About me
●
This talk is not about
●
Introduction
●
Definitions
●
OpenGL
●
3D Pipeline Overview
●
3D Rendering Topics
●
Shaders and the “future” of 3D development
●
Conclusion
May 23, 2009 Tchelinux 2009 21

22. 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?
May 23, 2009 Tchelinux 2009 22

23. 3D Pipeline
http://www.lighthouse3d.com/opengl/glsl/index.php?pipeline
May 23, 2009 Tchelinux 2009 23

24. 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.
May 23, 2009 Tchelinux 2009 24

25. 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.
May 23, 2009 Tchelinux 2009 25

26. 3D Pipeline – Assembly
●
So far, we only have
vertices, coordinates.
●
Besides vertices, we have also provided
the information on how to connect them.
May 23, 2009 Tchelinux 2009 26

27. 3D Pipeline - Rasterization
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Very important step!
●
Your eyes trick you:
Your screen is 2D.
●
Rasterization: converting from the 3D
space into the “plane” screen space.
Fragments.
May 23, 2009 Tchelinux 2009 27

28. 3D Pipeline - Interpolation
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Finally, we perform interpolation between
the fragments.
●
That is: calculate the color on each pixel,
based on the colors at the vertices.
May 23, 2009 Tchelinux 2009 28

29. 3D Pipeline
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That's it.
●
●
You now have base knowledge on how it
goes for rendering geometry, in a few
simple steps!
May 23, 2009 Tchelinux 2009 29

30. 3D Pipeline
●
To finish with it, here is a more complete
(and complex) pipeline model:
May 23, 2009 Tchelinux 2009 30

31. ●
About me
●
This talk is not about
●
Introduction
●
Definitions
●
OpenGL
●
3D Pipeline Overview
●
3D Rendering Topics
●
Shaders and the “future” of 3D development
●
Conclusion
May 23, 2009 Tchelinux 2009 31

32. 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
May 23, 2009 Tchelinux 2009 32

33. 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?
May 23, 2009 Tchelinux 2009 33

34. 3D Rendering Topics
●
Well, this might happen:
May 23, 2009 Tchelinux 2009 34

35. 3D Rendering Topics
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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.
May 23, 2009 Tchelinux 2009 35

36. 3D Rendering Topics
●
Depth testing works!
●
However, you shouldn't rely on that only.
●
For large sceneries, checking every
fragment could be very slow. :(
May 23, 2009 Tchelinux 2009 36

37. 3D Rendering Topics
●
Ok, think on this:
Could you ever possibly see anything
inside the building from here?
May 23, 2009 Tchelinux 2009 37

38. 3D Rendering Topics
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Probably not.
●
In this case, wouldn't it be wise to discard
everything inside it, ahead of time?
May 23, 2009 Tchelinux 2009 38

39. 3D Rendering Topics
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We can extend this even more:
●
We can't see behind that door. We can
discard that part of the map.
May 23, 2009 Tchelinux 2009 39

40. 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.
May 23, 2009 Tchelinux 2009 40

41. 3D Rendering Topics
Doom was only possible back then
because of Space Partitioning!
May 23, 2009 Tchelinux 2009 41

42. 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.
May 23, 2009 Tchelinux 2009 42

43. 3D Rendering Topics
May 23, 2009 Tchelinux 2009 43

44. 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.
May 23, 2009 Tchelinux 2009 44

45. 3D Rendering Topics
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Detailed scenery?!
●
Textures are a cheap way to add realism.
May 23, 2009 Tchelinux 2009 45

46. 3D Rendering Topics
●
Modeling: how can models made in 3D
modelers be added to the OpenGL
Pipeline?
May 23, 2009 Tchelinux 2009 46

47. 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 :)
May 23, 2009 Tchelinux 2009 47

48. ●
About me
●
This talk is not about
●
Introduction
●
Definitions
●
OpenGL
●
3D Pipeline Overview
●
3D Rendering Topics
●
Shaders and the “future” of 3D development
●
Conclusion
May 23, 2009 Tchelinux 2009 48

49. 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.
May 23, 2009 Tchelinux 2009 49

50. Shaders and the “future”
●
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...
May 23, 2009 Tchelinux 2009 50

51. Shaders and the “future”
Cell Shading
Per Pixel Lighting
May 23, 2009 Tchelinux 2009 51

52. Shaders and the “future”
●
OpenGL currently supports Vertex
Shaders and Pixel Shaders.
●
Let's take a look on the new pipeline,
with shaders in!
May 23, 2009 Tchelinux 2009 52

53. Shaders and the “future”
May 23, 2009 Tchelinux 2009 53

54. Shaders and the “future”
●
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.
May 23, 2009 Tchelinux 2009 54

55. ●
About me
●
This talk is not about
●
Introduction
●
Definitions
●
OpenGL
●
3D Pipeline Overview
●
3D Rendering Topics
●
Shaders and the “future” of 3D development
●
Conclusion
May 23, 2009 Tchelinux 2009 55

56. 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.
May 23, 2009 Tchelinux 2009 56

57. 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
May 23, 2009 Tchelinux 2009 57

58. Thank you!
Érico de Morais Nunes
nunes.erico@gmail.com
May 23, 2009 Tchelinux 2009 58