Full Inverse-Quadratic-Equation Lamp Falloff

This patch adds a new `falloff_type` ('Inverse Coefficients') for Lamps in
Blender-Internal and GLSL.

The current falloff modes use a formula like this inverse-square one:

`I = E × (D^2 / (D^2 + Q × r^2))`

While such a formula is simple for 3D-artists to use, it's algebraically
cumbersome to work with. Game-designers authoring their own shaders
could benefit much more by having direct control of falloff-coefficients:

`I = E × (1.0 / (coefC + coefL × r + coefQ × r^2))`

In this mode, the `distance` parameter is unused (except for 'Sphere'
mode); instead relying on the designer to mathematically-model the
falloff-behavior.

The UI has been patched like so:
{F153843}

Reviewers: brecht, psy-fi

Reviewed By: psy-fi

Subscribers: brita_, antidote, campbellbarton, psy-fi

Differential Revision: https://developer.blender.org/D1194

1 files changed, 22 insertions, 0 deletions

diff --git a/source/blender/makesrna/intern/rna_lamp.c b/source/blender/makesrna/intern/rna_lamp.c
index 85a2623dc35..b6b97d37c0f 100644
--- a/source/blender/makesrna/intern/rna_lamp.c
+++ b/source/blender/makesrna/intern/rna_lamp.c
@@ -420,6 +420,7 @@ static void rna_def_lamp_falloff(StructRNA *srna)
 		{LA_FALLOFF_CONSTANT, "CONSTANT", 0, "Constant", ""},
 		{LA_FALLOFF_INVLINEAR, "INVERSE_LINEAR", 0, "Inverse Linear", ""},
 		{LA_FALLOFF_INVSQUARE, "INVERSE_SQUARE", 0, "Inverse Square", ""},
+		{LA_FALLOFF_INVCOEFFICIENTS, "INVERSE_COEFFICIENTS", 0, "Inverse Coefficients", ""},
 		{LA_FALLOFF_CURVE, "CUSTOM_CURVE", 0, "Custom Curve", ""},
 		{LA_FALLOFF_SLIDERS, "LINEAR_QUADRATIC_WEIGHTED", 0, "Lin/Quad Weighted", ""},
 		{0, NULL, 0, NULL, NULL}
@@ -451,6 +452,27 @@ static void rna_def_lamp_falloff(StructRNA *srna)
 	RNA_def_property_range(prop, 0.0f, 1.0f);
 	RNA_def_property_ui_text(prop, "Quadratic Attenuation", "Quadratic distance attenuation");
 	RNA_def_property_update(prop, 0, "rna_Lamp_draw_update");
+
+	prop = RNA_def_property(srna, "constant_coefficient", PROP_FLOAT, PROP_NONE);
+	RNA_def_property_float_sdna(prop, NULL, "coeff_const");
+	RNA_def_property_range(prop, 0.0f, FLT_MAX);
+	RNA_def_property_ui_text(prop, "Constant Coefficient",
+							 "Constant distance attenuation coefficient");
+	RNA_def_property_update(prop, 0, "rna_Lamp_draw_update");
+
+	prop = RNA_def_property(srna, "linear_coefficient", PROP_FLOAT, PROP_NONE);
+	RNA_def_property_float_sdna(prop, NULL, "coeff_lin");
+	RNA_def_property_range(prop, 0.0f, FLT_MAX);
+	RNA_def_property_ui_text(prop, "Linear Coefficient",
+							 "Linear distance attenuation coefficient");
+	RNA_def_property_update(prop, 0, "rna_Lamp_draw_update");
+
+	prop = RNA_def_property(srna, "quadratic_coefficient", PROP_FLOAT, PROP_NONE);
+	RNA_def_property_float_sdna(prop, NULL, "coeff_quad");
+	RNA_def_property_range(prop, 0.0f, FLT_MAX);
+	RNA_def_property_ui_text(prop, "Quadratic Coefficient",
+							 "Quadratic distance attenuation coefficient");
+	RNA_def_property_update(prop, 0, "rna_Lamp_draw_update");
 }
 
 static void rna_def_lamp_shadow(StructRNA *srna, int spot, int area)