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_define.h b/source/blender/makesrna/RNA_define.h
index 17309d847bd..a31182b2f5a 100644
--- a/source/blender/makesrna/RNA_define.h
+++ b/source/blender/makesrna/RNA_define.h
@@ -388,6 +388,7 @@ void RNA_def_property_string_default(PropertyRNA *prop, const char *value);
 void RNA_def_property_ui_text(PropertyRNA *prop, const char *name, const char *description);
 void RNA_def_property_ui_range(
     PropertyRNA *prop, double min, double max, double step, int precision);
+void RNA_def_property_ui_scale_type(PropertyRNA *prop, PropertyScaleType scale_type);
 void RNA_def_property_ui_icon(PropertyRNA *prop, int icon, int consecutive);
 
 void RNA_def_property_update(PropertyRNA *prop, int noteflag, const char *updatefunc);