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How Now, Shader Cow? -- CS 519 Class of 2007

HDR COW

Ray Lin

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What is HDR?

• Dynamic Range – Ratio between highest and lowest luminance

• High Dynamic Range– Much higher and/or lower than 0.0~1.0 range

How It Does

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What It Looks Like

1 Original Texture

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Downsample

Compute Average Iuminance

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Brightness Filter

Gaussian Blur

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Gaussian Blur

Final Blending

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What If Over Exposure?

HOW NOW SHADER COW

CS 519 Shader Cow ProjectChristopher Moore

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Details

• 1) Render the Scene to the Scene Tex

Details

• 2) Render the Advection with theLast Advection Tex

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Details

• 3) Blend the Scene Tex &Advectioninto theNext Advection Tex

Details

• 4) Dump Next Advection Tex to Screen

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Details

• 5) Swap Advection Textures

Viola

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Tweakable Parameters

• Advection Distance• Typically one over texture size

• Gradient Sampling Distance• Typically the same thing

• Flip the Height Map?• Not technically correct but looks good

• Transform from gradient to advection• Advect along gradient or along edges

Examples

• Original Scene

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Impressionist• Use the background

texture for height map• Flip the height map• Advect along edges

(don’t tell anyone, but it only works well with the dandelion background)

Claude Moo-net

Pointillist• Use the background

texture for height map• Flip the height map• Advect along gradient

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Watercolor• Use the background

texture for height map• Large gradient steps

Stained Glass• Use scene tex for

height map• Advect against gradient

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Cellular• Use last advect tex for

height map• Advect against gradient

Glowing• Use last advect tex for

height map• Advect along gradient

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In The End

Pen & Ink Cow – Nick Hogle

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Pen & Ink Cow

• Used a “Tonal Art Map” as described by Hughes Hoppe in “Fine Tone Control in Hardware Hatching”

• Simulated 3d texturing in fragment shader using a single 2d texture

• Requires a smooth parameterization of model

Tonal Art Map

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Another Viewpoint

Bull Caricature: Scott ProperThe cow was morphed with two spheres in the GLSL vertex shader to achieve the appearance of a bull caricature. Parameters control each sphere’s size, height, and separation.

Several parameters control how the spheres are morphed with the cow:•“Blend” – How closely each vertex of the cow was blended with the sphere vertices•“Object Width” – Size of the cow. Controls how vertices of two spheres are blended prior to being blended with cow vertices•“Sphere Offset” – Controls how vertices on cow match up to vertices on spheres.

Several noise parameters are combined to give the cow the appearance of a Holstein. 3D noise was used to eliminate the problem of greater-frequency noise on the underbelly of the cow.

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Further examples

“Datchund Cow”

“A Big Caboose”

Sphere offset low Sphere offset high

Object width low Object width high

http://ww

w.codem

onsters.de/

html/textures_cubem

aps.html

Jacob Lee

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http://engr.oregonstate.edu/

~leechu/OSU

/519/MA

RSC

OW

.HTM

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EnglishChineseArabicKorean UnknownTaiwaneseJapaneseHebrew

• Cubemap – Cloudy hills fromhttp://www.codemonsters.de/html/textures_cubemaps.html

• Distorting the cow. Then discarding parts of it.• Stuck on the Lens Effect – quad drawn in eye co-

ordinates, right in front of the eye. With parts discarded, then blended.

Flying CowKannan Jeyakuma

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Code Bits

Cow Distortion - Vertex Displacementvec4 vert = gl_Vertex + vec4(sin(gl_Vertex.y*1*Distortion),-sin(gl_Vertex.z*2*Distortion),0,1)*t;

Lens Effect – Vertex Shadergl_Position = vec4(gl_Vertex.xy, 0.1, 1.0);

Fragment ShadersBasically use noise to calculate a threshold. Then discard some pixels. Then take the colors and mix them.

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Yoga Cow

A cow bending and twisting through a vertex shader

Adam Leibel

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• The coordinates are in Cartesian form, but one dimension is fixed in each transformation.

• Convert from Cartesian to Polar, adjust the angle, then convert back.

Cartesian -> Polar Polar -> CartesianR=√(X2+Y2) X= R*cos(φ)φ=tan-1(Y/X) Y= R*sin(φ)

Bullet-Time Cow?

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How-Now-Shader-Cow

“the lava cow” by William Brendel

Goal

• To create a “lava effect” shader, I need:– a noisy black-to-red-to-yellow texture

– some bump mapping on the cracks between lava and rocks

– a Phong illumination model

– a glow effect due to the lava heat diffusion

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The lava texture

• First set the background to BLACK

• Then create an elliptical Polka dots pattern

• Displace the ellipses using Perlin noise

• Create a color ramp from RED on the edge to YELLOW on the center of each ellipse

Bump mapping

• On the edge of each ellipse, the normal should be almost tangent to the surface

• If equ = [(x-xcenter)/Ad]2 + [(y-ycenter)/Bd]2

• Normal = (1-equ)*Normal + equ*Tangent

• Use Gram-Schmidt equation to find the Tangent

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Phong illumination model

• Illumination model based on Gouraud shading

Glow effect

• Multi pass in the shader to blur the silhouette

• Fake effect: add some lighting on the silhouette instead

• when dot(dirToEye,Normal) almost 0

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ResultsGlow effect

on the silhouette

Phong illumination

Noisy “lava”procedural 3D texture

Bump mapping on

the edge

Russian Stacking Cow DollsJonathan Dodge

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• First, noisify u,v coordinates• Compute an ellipse based on uv,vv• Do Noisy elliptical dots• … But only if a noise value is above a

threshold• Post-Processing (hooves/face/horns)• Lighting• Post-Post-Processing (slash a rectangular

hole in the side, using slightly noisy xyz)

Cow Coming Out of Warp

Ben Weiss

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8.0218.0

21 −+−= vut

Randy Rauwendaal

ASCII Cow

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The Code

uniform sampler3D ascii_texture;uniform sampler2D image_texture;

uniform float size;uniform float inv_size;

void main(void){

vec3 lumRGB = vec3(0.3, 0.59, 0.11);

vec2 asciiBase = gl_TexCoord[0].ts * size;

vec4 image = texture2D(image_texture, (floor(asciiBase) + 0.5) * inv_size);

float luminance = dot(image.rgb, lumRGB);

vec3 index = vec3(luminance, asciiBase);

vec4 ascii = texture3D(ascii_texture, index);

vec4 result = ascii * image;

gl_FragColor = result;}

All The Other Stuff

• Convert 2D ASCII bitmap to 3D ASCII Texture

• Render Scene to Texture using Frame Buffer Objects http://www.gpgpu.org/developer/

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Traditional Inventiveness

• Like many images, my cow was the result of a misunderstanding compounded by an accident shot through with typographic errors.

• But hey, it looked awesome.

Benjamin Brewster

Mistakes and Confessions

• My primary mistake was when I had programmed this line:

• noiseMagnitude = noise(xcomp(P) * 8.0) + noise(ycomp(P) * 8.0) + noise(zcomp(P) * 15.0)

• This causes noise, but is not “jaggy”– I tried everything I could do for jaggies.

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Revelations

• Clearly, I was missing the concept of octaves.

• It’s the octaves that cause high detail, high resolution noise on top of the low detail curviness that is first octave noise.

Pretty Errors

Islands are results of Z component

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Recriminations

• My final cow shot is not exactly the same shader… because I threw it away as a (pretty) mistake.

• The end result I found, though, looks like a circuit board, especially when colored correctly.

Proverbial proof-proving pudding

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Arrow’d Cow

XY Axis

Funny circles

Trojan CowSwamy Korada

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Procedural wooden texture applied over the cow.The wood is composed of light and dark areas alternating in concentric cylinders with noise added to warp the cylinders to create a more natural looking pattern.Pattern of the wooden texture is different in each rectangular piece as noise generated is dependent on the texture co-ordinates of each piece.

How Now Holo-cow

Will Dillon

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Normal map; rgb = xyzapply the normal

matrixuse it as a color! ☺

Discard TheseDiscard These

Put the hologram herePut the hologram here

color = normalize( gl_NormalMatrix * textureColor );

Environment map Environment map reflectionsreflectionsnormal map normal map ““hologramhologram””

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Nadia PayetTexture-based Bump-mapped cows

• Compute normal map of texture• Get texture coords of neighboring pixels

vec2 st1 = vec2(s+ds,t);

• Get corresponding colorvec4 c1 = texture2D(TexUnit,st1);

• Compute intensity of texture therefloat h1 = 0.299*c1.r + 0.587*c1.g + 0.114*c1.b;

• Normal is thenvec3 normal = vec3(20.*(h1-h2),20.*(h3-h4),1.);

h4

h1h2

h3

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How to apply texture to cow• Used a sin function with frequency and phase

x = 0.5*(sin(x*Freq+Phase)+1.);y = 0.5*(sin(y*Freq)+1.);vec2 st = vec2(x,y);

• Still stretched around the head

Now apply bump-mapping • Read normals from normal map• Convert them to WC• Apply lighting with these

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Wine Cow

William &

Nadia

First step – Glass cow

• Use Mike’s code of refractive cow• Add Phong illumination• Red reflection from wine on silhouette• Tune alpha value

– When shiny spot, alpha is close to 1.– When far from specular spot, alpha close to 0.

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Second step – Wine

• Thought of doing the level with slider but– Setting vertex.y = level– Discarding when vertex.y > level

• So we chose to fix the level and use this model for the inside

Add red spot in the middle

• Use ellipse equation• Add noise• Mix colors according to distance from the

center of ellipse (fog equation)

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The results

The results

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The results

Well done, Everyone !

Cheers! (hic)