Assignment #3 Which is something you may wish to do since it is - - PDF document

So You Want to Write some Procedural Shaders

Assignment #3

• Which is something you may wish to do

since it is Assignment #3

• In fact…

Assignment #3

• Goal is to be able to produce something nicer than

this:

Assignments

• Some advice:

– Choose either #1 (Ray tracing) or #2 (radioisity) – #3 will be real time shading…

• Challenge will be getting environment set up

– #4 – Tone Reproduction

• Modification of #1 or #2
• In fact

– If you choose to do assignments 1 & 2, you need not do any other.

• so…pleasant dreams!

Assignment #3

• Experimentation with procedural shaders
• Three goals:

– Download and install a procedural shading system. – Learn the logistics of assigning a shader to an

• bject

– Create/use 3 simple shaders

Assignment #3

• 1. Download:

– Cg – Real time shading language (Nvidia)

• Support for DirectX 8, 9 and OpenGL1.4
• Supposedly graphics card independent
• Download:

– http://developer.nvidia.com – Programming environment for Windows only using Visual Studio.

Assignment #3

• 1. Download

– RenderMonkey

• For ATI Cards
• DirectX 8.1+ Support only
• http://www.ati.com/developer/sdk/radeonSDK/html/Tools/RenderMonkey.html

Assignment #3

• If you do not have Visual Studio or if your

graphics card is not up to par.

– Renderman shaders

• Blue Moon Rendering Tools – no longer distributed

but…

– I can get last version for Windows and Linux/Intel

• Aqsis – Open Source Renderman renderer

– Win32 and MacOS X – http://www.aqsis.com

Assignment #3

• 2. Attach shaders to objects

– Run the tutorial supplied with the system. – For Cg users

• http://graphics3d.com/guides/cg/index.html

– For Renderman users

• BMRT docs
• Renderman for Poets:

– http://www.cs.utexas.edu/users/amenta/eog/poets.pdf

Assignment #3

• 3. Create / use simple shaders

– Three required:

• Phong
• Brick Shader
• Grab-bag (one of your choice)

Assignment #3

• Image Deliverable

phong brick Your choice

Assignment #3

• A note on “borrowing” shaders

– Shaders are like Makefiles

• Best to take one that works and modify

– Not only allow but encourage use of others shaders

• cgshaders.org
• Renderman repository

– http://www.renderman.org/RMR/RMRShaders.html

Assignment #3

• A note on “borrowing” shaders

– If you do use other’s shaders, you must

• Attribute the source
• Allow or show results of changing shader

arguments.

Assignment #3

• Deliverables

– This laptop has a Gforce 4 graphics card. – If Cg

• Shader code
• Executable
• Instructions on using

– If non-Cg

• Shader code
• Multiple Screen dumps w/varying shader arguments or
• Personal demo on your own PC

– If Renderman

• Shader code
• Multiple renderings w/varying shader arguments

Assignments

• Grading

– Each assignment is worth 20 points:

• 5 points – for something that compiles
• 10 points – for something that runs incorrectly
• 15 points – for something that runs correctly
• 20 points – something that runs + extras

– Well structured and documented code – Additional bells and whistles

Bells and Whistles

• 15 points

– Produce single image

• 20 points

– Produce multiple or interactive image with changing shading argument values

• Note

– Please, please, please submit readable and documented code!

Due dates

• If doing both assn 1 & 2

– Are you still sleeping?

• If doing assn 1 OR assn 2

– Due Feb 6th

Questions so far

Real time shading – Cg

Cg – vertex and fragment programs

Application Vertex Processor Fragment Processor

Assembly & Rasterization Framebuffer Operations

Framebuffer Textures

Program Program

Cg – Cg Runtime

• Just in Time (JIT) compiler for Cg shaders

– Shaders are compiled and loaded at run-time rather than linked with executable – Flexibility

• instant support for variety of graphics platforms
• Questions on Cg?

Another brick in the wall

• Building a brick shader

– Brick shader will actually be a procedural texture that is mapped onto a surface – Texture coordinates s, t

Building a brick shader

BRICKWIDTH BRICKHEIGHT MORTARTHICKNESS

1 1

Building a brick shader

#define BRICKWIDTH 0.25 #define BRICKHEIGHT 0.08 #define MORTARTHICKNESS 0.01 #define BMHEIGHT (BRICKHEIGHT + MORTARTHICKNESS) #define BMWIDTH (BRICKWIDTH + MORTARTHICKNESS)

Building a brick shader

surface brick ( uniform Color Cbrick = color (0.5, 0.15, 0.1); uniform Color Cmortar = color (0.5, 0.5, 0.5) ) { // What row is the point in question on float row = t / BMHEIGHT; // If even, offset length by a half if ( row % 2 == 0) s += (BMWIDTH/2);

Building a brick shader

// wrap texture coords to see where on given brick // you are s = s % width; t = t % height; // Set the color based on where you are Color Ct = Cbrick; if (s < MORTARTHICKNESS || t < MORTARTTHICKNESS) Ct = Cmortar // Return correct color Cs = Ct; }

Building a better brick shader

• Let’s use noise to discolor individual bricks

Building a better brick shader

// Set the color based on where you are // Let the brick color change based on noise float noiseChange = 0.1; float row = s / BMWIDTH; Color Ct = Cbrick + (noise (row,col) * noiseChange); if (s < MORTARTHICKNESS || t < MORTARTTHICKNESS) Ct = Cmortar // Return correct color Cs = Ct; }

Building an even better brick shader

• Other possible additions

– Bump mapping to have normal dip in mortar and rise on side of brick – Add noise to individual points on each brick – Add graininess – See brick shader for your given system

Questions?