Graphics Reference
In-Depth Information
API for handheld and embedded devices and then modify it to meet the
needs and constraints of the handheld and embedded device space. In the
earlier versions of OpenGL ES (1.0, 1.1, and 2.0), the device constraints
that were considered in the design included limited processing capabilities
and memory availability, low memory bandwidth, and sensitivity to
power consumption. The working group used the following criteria in the
definition of the OpenGL ES specification(s):
• The OpenGL API is very large and complex, and the goal of
the OpenGL ES working group was to create an API suitable for
constrained devices. To achieve this goal, the working group removed
any redundancy from the OpenGL API. In any case where the same
operation could be performed in more than one way, the most useful
method was taken and the redundant techniques were removed.
A good example of this is seen with specifying geometry, where in
OpenGL an application can use immediate mode, display lists, or
vertex arrays. In OpenGL ES, only vertex arrays exist; immediate mode
and display lists were removed.
• Removing redundancy was an important goal, but maintaining
compatibility with OpenGL was also important. As much as possible,
OpenGL ES was designed so that applications written to the embedded
subset of functionality in OpenGL would also run on OpenGL ES.
This was an important goal because it allows developers to leverage
both APIs and to develop applications and tools that use the common
subset of functionality.
• New features were introduced to address specific constraints of
handheld and embedded devices. For example, to reduce the power
consumption and increase the performance of shaders, precision
qualifiers were introduced to the shading language.
• The designers of OpenGL ES aimed to ensure a minimum set of
features for image quality. In early handheld devices, the screen sizes
were limited, making it essential that the quality of the pixels drawn
on the screen was as good as possible.
• The OpenGL ES working group wanted to ensure that any OpenGL
ES implementation would meet certain acceptable and agreed-on
standards for image quality, correctness, and robustness. This was
achieved by developing appropriate conformance tests that an
OpenGL ES implementation must pass to be considered compliant.
Khronos has released four OpenGL ES specifications so far: OpenGL ES 1.0
and ES 1.1 (referred to jointly as OpenGL ES 1.x in this topic), OpenGL
ES 2.0, and OpenGL ES 3.0. The OpenGL ES 1.0 and 1.1 specifications
