NON-PHOTOREALISTICRENDERING

- HATCHING & PENCIL DRAWING -

GM(Graphics Masters)CSE 20011266 이동형CSE 20021139 최태준CSE 20061174 신재훈

What is hatching?

A type of NPR(Non-photorealistic rendering)

Describes object using parallel or cross lines Contour , tone, and curvature are repre-

sented by those lines.

Density of lines and their overlaps are majorfactors to consider in implementing hatching.

Picture from Wikipedia

Develop Environment

OpenGL Visual Studio 2005 C++ Other Resources

OBJ files Jpeg decoder : CxImage Library GTS Library(GNU Triangulated Surface Library) Tone Texture : RenderMonkey SDK OBJ2GTS : Selfmade App For Converting

Implemented Features

Major Issues Contour Tone Curvature

Our Own Features Speed Lines Animation Tests

Major Issues - Contour

Contour shaking Multiple Contour drawing

Picture from “Real-Time Pencil Rendering”

Implemented Contour

Detection Contour1. Select two faces2. Check angle between two faces using Normal

Vector3. If angle < 150 then • If two faces share same edge then• Assign Contour

- Additional Check Routine : Suggestive contours for convey-ing shape

Draw Contour1. Draw additional two lines2. Edge’s Vertex(x,y,z) => Line’s Vertex(x+r,

y+r, z+r)3. r = -0.002 ~ +0.002

Result - Contour

Major Issues - Tone

Discrete multiple level of tones Mipmap for scaling Interpolation at each vertex

Picture from “Real-Time Hatching”

Tone Texture – RenderMonkey SDK

Weight : 0 Weigh : 1 Weight : 2

Weight : 3 Weigh : 4 Weight : 5

For each FaceFor each Vertex

1) v = Normalize(VertexCoord – LightCoord)2) n = VertexNormalVector3) result = (v.DotProduct(n) + 1.0f) * 3.0f4) weighting(result) • Weight => 0.0 ~ 6.0

5) Blend Texture Image - MultiTexture• If weight is 3.4 => weight 3 : 60%, weight 4 :

40%• If weight is 5.5 => weight 5 : 50%, weight 5 :

50%

Implemented - Tone

Result - Tone

Issue - Curvature

Rotate textures for voluminousness 3-way Blending• Each Vertex Per Face - Compute principal di-

rection Use GNU Triangulated Surface Library(

http://gts.sourceforge.net/)

* From “Real-Time Pencil Rendering” paper

For each FaceFor each Vertex

1) Get Principal Directions of Vertex2) angle = arctan(y / x)

x : x of principal directionsy : y of principal directions

3) Rotate texture by angle4) Texture Mapping

Implemented - Curvature

Result - Curvature

Our own Features – Speed Line

To express speed effectively in hatching, we used extra lines.

The faster object moves, the longer lines are drawn.

Speed line is expressed with gradation to express gradual speed change

Result – Speed Line

Our own Features – Flag

Flag animation is rendered to show that hatching can well render dynamic scenes.

Flag is set by basic rectangular lattice.

Flag animation is done as z value changes along sin function.

Like water animation.

Result – Flag

Q & A

Any questions?