cbgfx: Add blend functions to calculate transparency

Up until now we have no way of adding transparency into our firmware
screens.  Add set_blend() and clear_blend() functions to store alpha
value and rgb values to calculate alpha blending in
calculate_colors().

BUG=b:144969091,b:160839199
BRANCH=puff
TEST=dut-control power_state:rec
     press ctrl-d
     Ensure background is dimmed when dialog pops up

Change-Id: I95468f27836d34ab80392727d726a69c09dc168e
Signed-off-by: Shelley Chen <shchen@google.com>
Reviewed-on: https://review.coreboot.org/c/coreboot/+/43358
Tested-by: build bot (Jenkins) <no-reply@coreboot.org>
Reviewed-by: Yu-Ping Wu <yupingso@google.com>
Reviewed-by: Julius Werner <jwerner@chromium.org>

0 files changed, 0 insertions, 0 deletions