S60 3rd Edition SDK for Symbian OS
Example Applications Guide

OpenGL ES Texture Example

1. About this Example
2. Prerequisites
3. Design and Implementation

1. About this Example

This example demonstrates texturing in OpenGL ES. Definition of textures, texture coordinates, and the use of texture matrix are shown. Textures are loaded from jpeg files using Image Converter Library. This example also demonstrates texture wrapping and combines lighting and blending with textures. Again, the user can change the setup by accessing the menu by pressing the left software button.

This example can be extended to any kind of OpenGL ES application, but you might want to look at the other example applications as well for how to use other, different kinds of, OpenGL ES features.

Only classes used by this example are the basic UI framework baseclasses. Open GL ES itself is pure C method call API and doesn't use classes.

2. Prerequisites

To build and run this example you need to have the S60 SDK installed and working correctly on your computer. You also need basic understanding on how to build S60 applications.

To work with this example application you need basic understanding on how to build S60 applications and basic undestanding of how Symbian (or COE) UI and application framework works. Also basic knowledge on OpenGL or OpenGL ES is required if you wish to modify the example.

3. Design and Implementation

In this example, a single cube that has its every side textured is created. In order to do this, duplication of the cube’s vertex coordinates is needed. Every vertex appears three times in the vertex list, with three different associated texture coordinates. See the definition of vertices from source code file Texture.cpp. Since there are two different textures, the cube has to be constructed from two different objects, each of which is assigned to a certain texture. Two different index lists are defined for this purpose: triangles and triangles2. Triangles contains indices for five sides of the cube, where the nasa_hubble texture is assigned, and triangles2 contains indices for the sixth side, where the ogles.jpg texture is assigned.

Texture coordinates are defined in the same way as the color values, that is, per vertex. Possible data types for texture coordinates are GL_BYTE, GL_SHORT, GL_FIXED, and GL_FLOAT. In this example, the defined coordinate type is GL_BYTE, and therefore the possible values are between [-128,127]. Both of the used texture sizes are 256x256 pixels.

After textures have been loaded with glTexImage2D(…), the original bitmaps can be deleted because the textures have been copied to OpenGL ES texture manager, that is, the textures are stored inside OpenGL ES. See the code in TextureAppUi.CPP for more information.When using lighting with texture mapping, the texture environment has to be changed from GL_REPLACE to GL_MODULATE.

The shading model should be set to GL_SMOOTH when using lighting. In this example, texture wrapping is implemented simply by changing the scale in texture matrix. Instead of scaling the texture coordinates by 1.f/255.f we scale them by 1.f/128.f. After that the texture coordinates are between [0,2], which causes the texture to wrap one time. See code in Texture.cpp.

Also use of blending can create nice-looking effects. In this example, blending is used to create a translucency effect. This effect can be enabled by pressing the joystick down.

3.1 Capabilities

The application has capability NONE as it only needs the rights to execute and access to the screen.

3.2 ScalableUI

All Open GL ES examples support various screen modes. The examples also support changing the screen size while the application is running.

This inheritance list is sorted roughly, but not completely, alphabetically: