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

7 files changed, 97 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);
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);
diff --git a/source/blender/makesrna/RNA_types.h b/source/blender/makesrna/RNA_types.h
index 6cd3678017e..4a6d6dddec7 100644
--- a/source/blender/makesrna/RNA_types.h
+++ b/source/blender/makesrna/RNA_types.h
@@ -95,6 +95,32 @@ typedef enum PropertyUnit {
   PROP_UNIT_TEMPERATURE = (11 << 16), /* C */
 } PropertyUnit;
 
+/**
+ * Use values besides #PROP_SCALE_LINEAR
+ * so the movement of the mouse doesn't map linearly to the value of the slider.
+ *
+ * For some settings it's useful to space motion in a non-linear way, see T77868.
+ *
+ * NOTE: The scale types are available for all float sliders.
+ * For integer sliders they are only available if they use the visible value bar.
+ * Sliders with logarithmic scale and value bar must have a range > 0
+ * while logarithmic sliders without the value bar can have a range of >= 0.
+ */
+typedef enum PropertyScaleType {
+  /** Linear scale (default). */
+  PROP_SCALE_LINEAR = 0,
+  /**
+   * Logarithmic scale
+   * - Maximum range: `0 <= x < inf`
+   */
+  PROP_SCALE_LOG = 1,
+  /**
+   * Cubic scale.
+   * - Maximum range: `-inf < x < inf`
+   */
+  PROP_SCALE_CUBIC = 2,
+} PropertyScaleType;
+
 #define RNA_SUBTYPE_UNIT(subtype) ((subtype)&0x00FF0000)
 #define RNA_SUBTYPE_VALUE(subtype) ((subtype) & ~0x00FF0000)
 #define RNA_SUBTYPE_UNIT_VALUE(subtype) ((subtype) >> 16)
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);
diff --git a/source/blender/makesrna/intern/rna_access.c b/source/blender/makesrna/intern/rna_access.c
index 9b57096ec19..150a455f1c7 100644
--- a/source/blender/makesrna/intern/rna_access.c
+++ b/source/blender/makesrna/intern/rna_access.c
@@ -1189,6 +1189,24 @@ PropertyUnit RNA_property_unit(PropertyRNA *prop)
   return RNA_SUBTYPE_UNIT(RNA_property_subtype(prop));
 }
 
+PropertyScaleType RNA_property_ui_scale(PropertyRNA *prop)
+{
+  PropertyRNA *rna_prop = rna_ensure_property(prop);
+
+  switch (rna_prop->type) {
+    case PROP_INT: {
+      IntPropertyRNA *iprop = (IntPropertyRNA *)rna_prop;
+      return iprop->ui_scale_type;
+    }
+    case PROP_FLOAT: {
+      FloatPropertyRNA *fprop = (FloatPropertyRNA *)rna_prop;
+      return fprop->ui_scale_type;
+    }
+    default:
+      return PROP_SCALE_LINEAR;
+  }
+}
+
 int RNA_property_flag(PropertyRNA *prop)
 {
   return rna_ensure_property(prop)->flag;
diff --git a/source/blender/makesrna/intern/rna_define.c b/source/blender/makesrna/intern/rna_define.c
index 2fdf7e5eaa7..9b9d561603b 100644
--- a/source/blender/makesrna/intern/rna_define.c
+++ b/source/blender/makesrna/intern/rna_define.c
@@ -1754,6 +1754,28 @@ void RNA_def_property_ui_range(
   }
 }
 
+void RNA_def_property_ui_scale_type(PropertyRNA *prop, PropertyScaleType ui_scale_type)
+{
+  StructRNA *srna = DefRNA.laststruct;
+
+  switch (prop->type) {
+    case PROP_INT: {
+      IntPropertyRNA *iprop = (IntPropertyRNA *)prop;
+      iprop->ui_scale_type = ui_scale_type;
+      break;
+    }
+    case PROP_FLOAT: {
+      FloatPropertyRNA *fprop = (FloatPropertyRNA *)prop;
+      fprop->ui_scale_type = ui_scale_type;
+      break;
+    }
+    default:
+      CLOG_ERROR(&LOG, "\"%s.%s\", invalid type for scale.", srna->identifier, prop->identifier);
+      DefRNA.error = true;
+      break;
+  }
+}
+
 void RNA_def_property_range(PropertyRNA *prop, double min, double max)
 {
   StructRNA *srna = DefRNA.laststruct;
diff --git a/source/blender/makesrna/intern/rna_internal_types.h b/source/blender/makesrna/intern/rna_internal_types.h
index 0c0260c889c..245730919b0 100644
--- a/source/blender/makesrna/intern/rna_internal_types.h
+++ b/source/blender/makesrna/intern/rna_internal_types.h
@@ -400,6 +400,7 @@ typedef struct IntPropertyRNA {
   PropIntArraySetFuncEx setarray_ex;
   PropIntRangeFuncEx range_ex;
 
+  PropertyScaleType ui_scale_type;
   int softmin, softmax;
   int hardmin, hardmax;
   int step;
@@ -423,6 +424,7 @@ typedef struct FloatPropertyRNA {
   PropFloatArraySetFuncEx setarray_ex;
   PropFloatRangeFuncEx range_ex;
 
+  PropertyScaleType ui_scale_type;
   float softmin, softmax;
   float hardmin, hardmax;
   float step;