UI: add non-linear slider support

This patch introduces non linear sliders. That means, that the movement
of the mouse doesn't map linearly to the value of the slider.

The following changes have been made.

- Free logarithmic sliders with maximum range of (`0 <= x < inf`)
- Logarithmic sliders with correct value indication bar.
- Free cubic sliders with maximum range of (`-inf < x < inf`)
- Cubic sliders with correct value indication bar.

Cubic mapping has been added as well, because it's used for brush sizes
in other applications (Krita for e.g.).

To make a slider have a different scale type use following line in RNA:
 `RNA_def_property_ui_scale_type(prop, PROP_SCALE_LOGARITHMIC);`
or:
 `RNA_def_property_ui_scale_type(prop, PROP_SCALE_CUBIC);`

Test the precision, step size and soft-min if you change the scale type
of a property as it will feel very different and may need tweaking.

Ref D9074

1 files changed, 1 insertions, 0 deletions

diff --git a/source/blender/makesrna/RNA_access.h b/source/blender/makesrna/RNA_access.h
index 54e077c624c..39a46948321 100644
--- a/source/blender/makesrna/RNA_access.h
+++ b/source/blender/makesrna/RNA_access.h
@@ -845,6 +845,7 @@ const char *RNA_property_description(PropertyRNA *prop);
 PropertyType RNA_property_type(PropertyRNA *prop);
 PropertySubType RNA_property_subtype(PropertyRNA *prop);
 PropertyUnit RNA_property_unit(PropertyRNA *prop);
+PropertyScaleType RNA_property_ui_scale(PropertyRNA *prop);
 int RNA_property_flag(PropertyRNA *prop);
 int RNA_property_override_flag(PropertyRNA *prop);
 int RNA_property_tags(PropertyRNA *prop);