Fall 2009 Revised 1

Texture Mapping (Intermediate)

Jyun-Ming Chen

Fall 2009 Revised 2

Texture Suite

highlightbubble

Fall 2009 Revised 3

Texture Suite

warp

underwater

Fall 2009 Revised 4

Outline

Dynamic sub texture image1D and 3D texturesRender to texture

Environment mapping Cubemap Spheremap

Bump map Light mapProjective textureQ coord

Fall 2009 Revised 5

Dynamic Texture

CopyTexSubImage2DReplace a rectangular portion of 2D texture with pixels from the current READ_BUFFERThis involves a read-back from GPU to CPU.

Can you think of a way to move the dynamic texture

around?!

A better way of doing it: Render-to-texture (RTT) with framebuffer object (FBO)

Fall 2009 Revised 6

glTexSubImage2D

Replace part of the original image as new subimageWidth and size of image need not be 2n

E.g., dynamic texture

glTexSubImage2D (target, level, xoffset, yoffset, width, height, format, type, pixels)

glTexSubImage2D (target, level, xoffset, yoffset, width, height, format, type, pixels)

Fall 2009 Revised 7

Other Related Functions

void glCopyTexImage2D(target, level, internalformat, x, y, width, height, border); defines a two-dimensional texture image with pi

xels from the current GL_READ_BUFFER.void glCopyTexSubImage2D(target, level, xoffset, yoffset, x, y, width, height); doc replaces a rectangular portion of a two-dimensi

onal texture image with pixels from the current GL_READ_BUFFER (rather than from main memory, as is the case for glTexSubImage2D).

Similar to glCopyPixe

ls

Fall 2009 Revised 8

3D Textures

Fall 2009 Revised 9

Render-to-Texture (RTT)Generate a snapshot every degrees Total 360/ shots

The shots are stored as a single texture Width and height

must be 2n

E.g., 128x128x8, =45

Fall 2009 Revised 10

RTT ImplementationFirst determine a viewing range such that all views are rendered well.The snapshots are taken from slightly elevated positions.At each position, pre-render to some 2^n resolution, copy the image to bufferWhen the panorama is done, set all pixels with background color to zero alpha values. Bind it to a texture object.

Fall 2009 Revised 11

RTTThe image version of the model will be set on a (cylindrical) billboardThe texture can be chosen as follows:

360

: take toImage

If you tank is symmetric, you can use even fewer images

Fall 2009 Revised 12

RTT (symmetric tank)

180°8 images: (180/726)° apartport side

starboard side Reverse the port-

side image

0

7

12

3

4

5

6

26

13: take toImage

Fall 2009 Revised 13

Perlin Noise                             

3D TextureNoise as texture

Fall 2009 Revised 14

Light Map

By Michael Gold (ref)NVIDIA

Fall 2009 Revised 15

Light MapsQuake (雷神之錘 , id software) was the first computer game to use light map

Fall 2009 Revised 16

Fall 2009 Revised 17

Lightmaps

Cached Lighting Results Reuse lighting calculations

Multiple local lights (same type) Static portion of scene’s light field Sample region with texture instead of

tessellating

Fall 2009 Revised 18

Lightmaps

Getting the most from the Lightmap Maximize lightmap re-use, minimize light

map size Texture size versus sampling level

Full surface texture with built-in lighting Small surface texture, small low-resolution li

ghtmap Adjust texture matrix to re-use lightmap

Dynamic lighting: track moving lights

Fall 2009 Revised 19

Lightmaps

Segmenting Scene Lighting Static vs. dynamic light fields Global vs. local lighting Similar light shape

Fall 2009 Revised 20

Lightmaps

Segmenting the lightfields

Dominant Lighting Local lighting

Fall 2009 Revised 21

Lightmaps

Moving Local Lights Recreate the texture; simple but slow Manipulate the lightmap

Translate to move relative to the surface Scale to change spot size Change base polygon color to adjust intensit

y Projective textures ideal for spotlights

Fall 2009 Revised 22

Lightmaps

Moving Local Lights

TranslateTexture

ScaleTexture

Change BasePolygon Intensity

Fall 2009 Revised 23

Lightmaps

Creating a lightmap Light white, tesselated surface with local

light Render, capture image as texture Texture contains ambient and diffuse lig

hting Texture can also be computed analyticall

y

Fall 2009 Revised 24

Lightmaps

Creating a lightmap

Render surfacelit by local light

Create a TextureMap from Image

Fall 2009 Revised 25

Lightmaps

Lightmap building tips Minimize texture resolution to match required s

ampling Edges of texture should have uniform intensity Light intensity change should be negligible at e

dges Don’t forget borders if you clamp the lightmap

Fill in border to match edge and corner Or use border color

Fall 2009 Revised 26

Lightmaps

Lightmap building tipsBoundary should have

constant value

Intensity changes fromlight should be minimalnear edge of lightmap

Fall 2009 Revised 27

Lightmaps

Lighting with a Lightmap Local light is affected by surface color an

d texture Two step process adds local light contrib

ution: Modulate textured, unlit surfaces with lightm

ap Add locally lit image to scene

Can mix OpenGL, lightmap lighting in same scene

Fall 2009 Revised 28

Lightmaps

Creating local contribution

Unlit Scene Lightmap Intensity Local LightContribution

Lightmap

Fall 2009 Revised 29

Lightmaps

Using Lightmaps Move lightmaps using texture matrix Distance from surface simulated by scali

ng texture and changing intensity Texgen maps lightmap to surfaces, overri

des local texture coordinates Can avoid changing model’s texture coordi

nates

Fall 2009 Revised 30

Projective Texture Mapping

Light source as

slide projector

Also generate shadows

Fall 2009 Revised 31

Projective Texture Mapping

Fall 2009 Revised 32

Implementation Tricks

The projected texture need to be padded with black boundary pixels so that the clamped texture appears OkSome natural faults (more than one layer of surface got textured): no way to resolve this!?

Fall 2009 Revised 33

Q coord

See Sampcode/qcoord

Fall 2009 Revised 34

Code Samples

Cutout textureRender-to-texture (RTT)

Whirlpool

cubemap

lightmap

billboarding