Supporting the fixed-function pipeline in OpenGL ES 2.0/3.0 implies that the API would support more than one way of implementing a feature, in violation of one of the criteria used by the working group in determining which features should be supported.The OpenGL ES working group decided against backward compatibility between OpenGL ES 2.0/3.0 and OpenGL ES 1.x for the following reasons: The texture color is combined with the diffuse color and the output of the previous texture combine stage with a fixed set of operations such as add, modulate, subtract, and dot. The fixed-function texture combine units implement a texture combine stage for each texture unit. Similarly, the programmable fragment shader replaces the fixed-function texture combine units implemented in OpenGL ES 1.x. The fixed-function vertex units implement a specific vertex transformation and lighting equation that can be used to transform the vertex position, transform or generate texture coordinates, and calculate the vertex color.

The OpenGL ES 2.0/3.0 programmable vertex shader replaces the fixed-function vertex units implemented in OpenGL ES 1.x. OpenGL ES 2.0/3.0 do not support the fixed-function pipeline that OpenGL ES 1.x supports. OpenGL ES 2.0 is not backward compatible with OpenGL ES 1.x. The fact that OpenGL ES 3.0 is backward compatible with OpenGL ES 2.0 differs from what was done for OpenGL ES 2.0 with respect to its backward compatibility with previous versions of OpenGL ES. Namely, framebuffer objects are no longer shared between contexts, cubemaps are always filtered using seamless filtering, and there are minor changes in the way signed fixed-point numbers are converted to floating-point numbers. There are some very minor changes to the later version that will affect a small number of applications in terms of backward compatibility.

This means that just about any application written to use OpenGL ES 2.0 will run on implementations of OpenGL ES 3.0. OpenGL ES 3.0 is backward compatible with OpenGL ES 2.0.

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