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3D Graphics with OpenGL ES and M3G- P20

3D Graphics with OpenGL ES and M3G- P20:Mobile phones are the new vehicle for bringing interactive graphics technologies to consumers. Graphics that in the 1980s was only seen in industrial flight simulators and at the turn of the millennium in desktop PCs and game consoles is now in the hands of billions of people. This book is about the technology underpinnings of mobile threedimensional graphics, the newest and most rapidly advancing area of computer graphics. | 174 OPENGL ES TRANSFORMATION AND LIGHTING CHAPTER 8 8.1.1 PRIMITIVE TYPES OpenGL ES 1.0 supports the geometric primitives shown in Figure 3.3 points lines and triangles. OpenGL ES 1.1 amends this list with point sprites. Points The point is the simplest OpenGL primitive and it requires only one vertex. Its primary property is its size which is set by the function void glPointSize fx type size . The point size corresponds to its diameter the total width defined in pixels and it defaults to 1. Points can be drawn either with or without antialiasing enabled and disabled with GL_POINT_SMOOTH . With antialiasing off the points are drawn as squares and the point size is rounded to the closest integer. With antialiasing enabled the points are drawn as circles and the alpha values of the pixels on the boundary are affected by how much the point covers those pixels. Even though points can be drawn quite efficiently in practice many graphics engines are optimized for rendering of triangles. This may mean that non-antialiased points are drawn as two triangles and the maximum point size for smooth points may be just one pixel. Similar optimizations may be used for line drawing. Point sprites and size attenuation OpenGL ES 1.1 provides features for points that are especially useful for particle effects point sprites point size arrays and point size attenuation. Many natural phenomena such as rain smoke or fire can be modeled by replicating several small pictures representing raindrops puffs of smoke or individual flames. The idea is that a set of points describes the positions of point sprites and their appearance comes from the current texture map. Section 9.2.8 describes how to apply a texture to points. When points are defined by an array in OpenGL ES 1.0 they all have the same size defined by glPointSize fx . In OpenGL ES 1.1 it is possible to give each point its own size see Section 8.1.2 and the point sizes may be attenuated by the distance between each point and the .