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, 27 insertions, 0 deletions

diff --git a/source/blender/makesrna/intern/makesrna.c b/source/blender/makesrna/intern/makesrna.c
index b20d9218316..ef65a99c73b 100644
--- a/source/blender/makesrna/intern/makesrna.c
+++ b/source/blender/makesrna/intern/makesrna.c
@@ -684,6 +684,29 @@ static char *rna_def_property_get_func(
         }
       }
     }
+
+    /* Check log scale sliders for negative range. */
+    if (prop->type == PROP_FLOAT) {
+      FloatPropertyRNA *fprop = (FloatPropertyRNA *)prop;
+      /* NOTE: UI_BTYPE_NUM_SLIDER can't have a softmin of zero. */
+      if ((fprop->ui_scale_type == PROP_SCALE_LOG) && (fprop->hardmin < 0 || fprop->softmin < 0)) {
+        CLOG_ERROR(
+            &LOG, "\"%s.%s\", range for log scale < 0.", srna->identifier, prop->identifier);
+        DefRNA.error = true;
+        return NULL;
+      }
+    }
+    if (prop->type == PROP_INT) {
+      IntPropertyRNA *iprop = (IntPropertyRNA *)prop;
+      /* Only UI_BTYPE_NUM_SLIDER is implemented and that one can't have a softmin of zero. */
+      if ((iprop->ui_scale_type == PROP_SCALE_LOG) &&
+          (iprop->hardmin <= 0 || iprop->softmin <= 0)) {
+        CLOG_ERROR(
+            &LOG, "\"%s.%s\", range for log scale <= 0.", srna->identifier, prop->identifier);
+        DefRNA.error = true;
+        return NULL;
+      }
+    }
   }
 
   func = rna_alloc_function_name(srna->identifier, rna_safe_id(prop->identifier), "get");
@@ -3935,6 +3958,8 @@ static void rna_generate_property(FILE *f, StructRNA *srna, const char *nest, Pr
               rna_function_string(iprop->getarray_ex),
               rna_function_string(iprop->setarray_ex),
               rna_function_string(iprop->range_ex));
+      rna_int_print(f, iprop->ui_scale_type);
+      fprintf(f, ", ");
       rna_int_print(f, iprop->softmin);
       fprintf(f, ", ");
       rna_int_print(f, iprop->softmax);
@@ -3969,6 +3994,8 @@ static void rna_generate_property(FILE *f, StructRNA *srna, const char *nest, Pr
               rna_function_string(fprop->getarray_ex),
               rna_function_string(fprop->setarray_ex),
               rna_function_string(fprop->range_ex));
+      rna_float_print(f, fprop->ui_scale_type);
+      fprintf(f, ", ");
       rna_float_print(f, fprop->softmin);
       fprintf(f, ", ");
       rna_float_print(f, fprop->softmax);