Change preserve option to command line switch

Changes each adjustment method to take a preserve parameter when
setting the temperature instead of parsing the preserve option
from the command line/configuration file. This helps resolve the
issues around #513:

- This allows the preserve option to be implemented as a
  command-line switch (-P). This switch _disables_ the preservation
  of existing gamma ramps. Having a command-line switch makes it
  easier to use directly with manual or one-shot mode.
- The preserve options is on by default, so continual mode as well
  as other modes will default to applying the color adjustment
  on top of the current gamma ramps.
- Preserve is always disabled in reset mode so resetting works
  as expected again.

1 files changed, 2 insertions, 0 deletions

diff --git a/src/options.h b/src/options.h
index 95a31b1..9993a07 100644
--- a/src/options.h
+++ b/src/options.h
@@ -34,6 +34,8 @@ typedef struct {
 	int temp_set;
 	/* Whether to fade between large skips in color temperature. */
 	int use_fade;
+	/* Whether to preserve gamma ramps if supported by gamma method. */
+	int preserve_gamma;
 
 	/* Selected gamma method. */
 	const gamma_method_t *method;