Fix log-scale rangesteps and log-control numeric spinboxes

diff --git a/libs/ardour/parameter_descriptor.cc b/libs/ardour/parameter_descriptor.cc
index 200987db8fe272250b9dde590cc8faeeec50d2fc..4f26af997d843087dca66a5c4d4ea6f5a7620ee6 100644 (file)
--- a/libs/ardour/parameter_descriptor.cc
+++ b/libs/ardour/parameter_descriptor.cc
@@ -200,25 +200,34 @@ ParameterDescriptor::update_steps()
                largestep = position_to_gain (dB_coeff_step(upper));
                step      = position_to_gain (largestep / 10.0);
                smallstep = step;
+       } else if (logarithmic) {
+               /* ignore logscale rangesteps. {small|large}steps are used with the spinbox.
+                * gtk-spinbox shows the internal (not interface) value and up/down
+                * arrows linearly increase.
+                * The AutomationController uses internal_to_interface():
+                *   ui-step [0..1] -> log (1 + largestep / lower) / log (upper / lower)
+                * so we use a step that's a multiple of "lower" for the interface step:
+                *   log (1 + x) / log (upper / lower)
+                */
+               smallstep = step = lower / 11;
+               largestep = lower / 3;
+               /* NOTE: the actual value does use rangesteps via
+                * logscale_to_position_with_steps(), position_to_logscale_with_steps()
+                * when it is converted.
+                */
        } else if (rangesteps > 1) {
                const float delta = upper - lower;
-               if (logarithmic) {
-                       smallstep = step = (powf (delta, 1.f  / (float)rangesteps) - 1.f) * lower;
-                       largestep = (powf (delta, std::max (0.5f, 10.f / (float)rangesteps)) - 1.f) * lower;
-               } else if (integer_step) {
+               if (integer_step) {
                        smallstep = step = 1.0;
                        largestep = std::max(1.f, rintf (delta / (rangesteps - 1.f)));
                } else {
                        step = smallstep = delta / (rangesteps - 1.f);
-                       largestep = std::min ((delta / 4.0f), 10.f * smallstep); // XXX
+                       largestep = std::min ((delta / 4.0f), 10.f * smallstep);
                }
        } else {
                const float delta = upper - lower;
                /* 30 steps between min/max (300 for fine-grained) */
-               if (logarithmic) {
-                       smallstep = step = (powf (delta, 1.f / 300.f) - 1.f) * lower;
-                       largestep = (powf (delta, 1.f / 30.f) - 1.f) * lower;
-               } else if (integer_step) {
+               if (integer_step) {
                        smallstep = step = 1.0;
                        largestep = std::max(1.f, rintf (delta / 30.f));
                } else {