Texture Mapping

Tom Kelliher, CS 320

Apr. 30, 2003

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Assignment

Work on project.

From Last Time

Light lab II.

Outline

1. Introduction to texture mapping.

2. A few issues/problems.

3. Example program: checker.c

Coming Up

Texture lab.

Introduction

1. What is a texture?

2. Why texture map? Complexity from simplicity.

3. Where can I get textures? Fixed patterns (polygon fills), texture generation functions, digitized images.

4. Do Web browsers texture map?

5. 1-D and 2-D textures.

A Little More Detail

1. Texture pattern: . Stored in texture memory as array of texels. (Texture memory and the rise of AGP.)

2. Texture mapping: mapping from T to object's geometric coordinates. (Must then map to screen coordinates.)

3. Possible problems: curved surfaces, closed surfaces, pixels not inverse mapping onto texels, aliasing.

4. How is a texture mapped to an object?
   1. texture and vertex coordinates.

   2. Range of texture coordinates.

   3. Wrapping modes: repeat, clamp.

5. How is it applied to an object?
   1. Modulation, decal.

6. Magnification and minification. Filters.

checker.c

Numbers in parentheses refer to line numbers in handouts.

1. Generation of a texture: makeCheckImage() (24).

   Interpretation?

2. Initializing: init() (39).
   1. Storage formats, texture handles and binding.

   2. Wrapping modes.

   3. Minification, magnification filters.

   4. glTexImage2D() --- ugh.

3. Rendering: display() (73).
   1. Enabling textures and specifying mapping mode.

   2. Specifying which texture.

   3. Binding texture and vertex coordinates.

4. Comparison of code with rendered results.

Experiments:

1. Is the lower right result a fluke? Rotate the lower left polygon and see what happens.

2. Specify a color for the polygons. Did anything change? Change the mode from GL_DECAL to GL_MODULATE and try again.

3. Individually change the GL_REPEATs to GL_CLAMPs and see what happens.