(cogl_gles2_wrapper_init): Get uniforms for fog parameters and
initialise them.
(cogl_wrap_glDrawArrays): Store the modelview matrix in a uniform
as well so that it can be used for fogging calculations.
(cogl_wrap_glEnable, cogl_wrap_glDisable): Enable/disable fogging.
(cogl_wrap_glFogx, cogl_wrap_glFogxv): Fill in wrapper to set
fogging parameters.
* clutter/cogl/gles/cogl-fixed-vertex-shader.glsl: Calculate the
fog amount if fogging is enabled.
* clutter/cogl/gles/cogl-fixed-fragment-shader.glsl: Mix with fog
color.
* clutter/cogl/gles/cogl-gles2-wrapper.h (CoglGles2Wrapper): Add
uniforms for fogging.
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