basic rendering methods - korea

Graphics

Graphics Lab @ Korea University http://kucg.korea.ac.kr

Basic Rendering Methods

Korea Univ.

Computer Graphics Lab.

KUCG

Graphics Lab @ Korea University

Polygon Shading

Spatial Coherence

Illumination calculations for pixels by the same primitive

http://kucg.korea.ac.kr

KUCG


Flat Shading

Constant-intensity Shading

OK for polyhedral objects

Not so good for ones with the smooth surfaces


KUCG


Flat Shading Process

One illumination calculation per polygon

All pixels inside each polygon will be the same color

i i

n

SiDALAE IKIKIKII ))RV()LN(( ii

Polygon Normal Vector


KUCG


Flat Shading in OpenGL

glShadeModel(GL_FLAT)


KUCG


Gouraud Shading

Intensity-interpolation Scheme

Produces smoothly shaded polygonal mesh

Shows some illumination highlights

Still can’t capture subtle lighting effects

Needs extremely fine mesh

Effectively reduced by Phong shading

<Flat Shading vs. Gouraud Shading>


KUCG


Gouraud Shading Process (1/2)

One lighting calculation per vertex

Interpolates pixels inside polygon

By using the colors computed at vertices

i i

n


Vertex Normal Vector

Viewer Light

N1

N3

V1 L1

Polygon

N2


KUCG


Vertex Normal Vector

Average of the surface normals

From polygons sharing that vertex

N2

N3

N4

N1


KUCG


Gouraud Shading Process (2/2)

Bilinearly interpolate colors at vertices

Down and across scan lines

I1

I2 I3

21 I1IA 31 I1IB

BA1I

I

1,,0


KUCG


Gouraud Shading in OpenGL

glShadeModel(GL_SMOOTH)


KUCG


Gouraud Shading of Highlights

by the Primitives’ Size & Location


KUCG


Phong Shading

Normal-vector interpolation shading

Can capture subtle illumination effects in polygon

interiors

Not supported by OpenGL/DirectX


KUCG


Phong Shading Process (1/2)

One lighting calculation per pixel

Approximate surface normals for inside points

Viewer Light

N3

V1 L1

Polygon

N2

i i

n


N1

Pixel Normal Vector


KUCG


Phong Shading Process (2/2)

Bilinearly interpolate surface normals at vertices

21 N1NA 31 N1NB

BA1N

N1

N3 N2

N


KUCG


Flat vs. Gouraud vs. Phong (1/2)


KUCG


Flat vs. Gouraud vs. Phong (2/2)

Wireframe Flat Shading

Gouraud Shading Phong Shading


KUCG


Wireframe


KUCG


Ambient Only


KUCG


Flat Shaded Polygons with

Diffuse Reflection


KUCG


Gouraud Shaded Polygons with

Diffuse Reflection


KUCG


Gouraud Shaded Polygons with

Specular Reflection


KUCG


Phong Shaded Polygons with

Specular Reflection


basic rendering methods - korea

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