Code review comment for lp:~vanvugt/mir/simplify-alpha

Needs discussion:
I left my thoughts on the Renderable interface here:
https://code.launchpad.net/~kdub/mir/fix-1373698/+merge/236023/comments/578069

Needs fixing:
95 + if (renderable->shaped() || renderable->alpha() < 1.0f)
108 + renderable->shaped() || renderable->alpha() < 1.0f,
We don't support planeAlpha blending in HWC yet, so we don't need the check of alpha() here just yet. The check in renderable_list_is_hwc_incompatible prevents these lines from being reached if plane alpha is present.

80 + if (// renderable->shaped() || // Unsafe to uncomment yet LP: #1374358
HWC can do alpha blending, so the commented out line should be removed.

62 -bool plane_alpha_is_translucent(mg::Renderable const& renderable)
Lets not remove this. I don't think the simpler check causes any 'real' problems, but since we're translating a float to an 8bit, anything greater than (1-2^9) should translate into 0xFF for the alpha value.