Since commit b4f5f1e461, the effect is eased in at the scroll
view's edges so that it does not appear out of nowhere. However,
the linear easing used is not the best option, as now the effect
appears so late that content near the edges ends up just being
cut off rather than faded out.
So adjust the easing function to have the effect appear faster.
https://bugzilla.gnome.org/show_bug.cgi?id=694327
Before version 1.2 of GLSL it would not implicitly convert from int to
float which meant that if you compare a float variable with an integer
constant it will generate a compile error. In particular this means
that on GLES2 (which uses GLSL 1.0) the scroll view shader will not
compile on pedantic compilers, which includes Mesa. This patch just
changes it to use floating point constants.
https://bugzilla.gnome.org/show_bug.cgi?id=693339
Cogl sets this for us since commit 2701b93f159bf2d3387cedf2d06fe921ad5641f3.
Setting it twice is illegal and causes compile failures:
error C0204: version directive must be first statement and may not be repeated.
This doesn't (or shouldn't) change the visual appearance of the fade
effect, but does do all the testing math inside the shader, rather
than on the CPU. This will make fading the offset much easier in
the future.
https://bugzilla.gnome.org/show_bug.cgi?id=689249
GLSL 1.20 is a better language, and we'll rely on it in future updates.
This doesn't have any additional constraints, since GLSL 1.20 was
standardized before GLSL-supporting drivers came out.
https://bugzilla.gnome.org/show_bug.cgi?id=689249
