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

3 files changed, 31 insertions, 2 deletions

diff --git a/source/blender/gpu/GPU_material.h b/source/blender/gpu/GPU_material.h
index 3bcc7e23f06..f150b7215e1 100644
--- a/source/blender/gpu/GPU_material.h
+++ b/source/blender/gpu/GPU_material.h
@@ -166,6 +166,9 @@ typedef enum GPUDynamicType {
 	GPU_DYNAMIC_LAMP_SPOTSIZE        = 10 | GPU_DYNAMIC_GROUP_LAMP,
 	GPU_DYNAMIC_LAMP_SPOTBLEND       = 11 | GPU_DYNAMIC_GROUP_LAMP,
 	GPU_DYNAMIC_LAMP_SPOTSCALE       = 12 | GPU_DYNAMIC_GROUP_LAMP,
+	GPU_DYNAMIC_LAMP_COEFFCONST      = 13 | GPU_DYNAMIC_GROUP_LAMP,
+	GPU_DYNAMIC_LAMP_COEFFLIN        = 14 | GPU_DYNAMIC_GROUP_LAMP,
+	GPU_DYNAMIC_LAMP_COEFFQUAD       = 15 | GPU_DYNAMIC_GROUP_LAMP,
 
 	GPU_DYNAMIC_SAMPLER_2DBUFFER     = 1  | GPU_DYNAMIC_GROUP_SAMPLER,
 	GPU_DYNAMIC_SAMPLER_2DIMAGE      = 2  | GPU_DYNAMIC_GROUP_SAMPLER,
@@ -318,7 +321,8 @@ float *GPU_lamp_dynpersmat(GPULamp *lamp);
 
 void GPU_lamp_update(GPULamp *lamp, int lay, int hide, float obmat[4][4]);
 void GPU_lamp_update_colors(GPULamp *lamp, float r, float g, float b, float energy);
-void GPU_lamp_update_distance(GPULamp *lamp, float distance, float att1, float att2);
+void GPU_lamp_update_distance(GPULamp *lamp, float distance, float att1, float att2,
+                              float coeff_const, float coeff_lin, float coeff_quad);
 void GPU_lamp_update_spot(GPULamp *lamp, float spotsize, float spotblend);
 int GPU_lamp_shadow_layer(GPULamp *lamp);
 GPUNodeLink *GPU_lamp_get_data(
diff --git a/source/blender/gpu/intern/gpu_material.c b/source/blender/gpu/intern/gpu_material.c
index cc401dc63c4..c32326889d1 100644
--- a/source/blender/gpu/intern/gpu_material.c
+++ b/source/blender/gpu/intern/gpu_material.c
@@ -148,6 +148,7 @@ struct GPULamp {
 	float spotvec[2];
 	float dyndist, dynatt1, dynatt2;
 	float dist, att1, att2;
+	float coeff_const, coeff_lin, coeff_quad;
 	float shadow_color[3];
 
 	float bias, d, clipend;
@@ -550,6 +551,12 @@ static GPUNodeLink *lamp_get_visibility(GPUMaterial *mat, GPULamp *lamp, GPUNode
 				         GPU_dynamic_uniform(&lamp->att1, GPU_DYNAMIC_LAMP_ATT1, lamp->ob),
 				         GPU_dynamic_uniform(&lamp->att2, GPU_DYNAMIC_LAMP_ATT2, lamp->ob), *dist, &visifac);
 				break;
+			case LA_FALLOFF_INVCOEFFICIENTS:
+				GPU_link(mat, "lamp_falloff_invcoefficients",
+					     GPU_dynamic_uniform(&lamp->coeff_const, GPU_DYNAMIC_LAMP_COEFFCONST, lamp->ob),
+					     GPU_dynamic_uniform(&lamp->coeff_lin, GPU_DYNAMIC_LAMP_COEFFLIN, lamp->ob),
+					     GPU_dynamic_uniform(&lamp->coeff_quad, GPU_DYNAMIC_LAMP_COEFFQUAD, lamp->ob), *dist, &visifac);
+				break;
 			case LA_FALLOFF_CURVE:
 			{
 				float *array;
@@ -2209,11 +2216,15 @@ void GPU_lamp_update_colors(GPULamp *lamp, float r, float g, float b, float ener
 	lamp->col[2] = b;
 }
 
-void GPU_lamp_update_distance(GPULamp *lamp, float distance, float att1, float att2)
+void GPU_lamp_update_distance(GPULamp *lamp, float distance, float att1, float att2,
+                              float coeff_const, float coeff_lin, float coeff_quad)
 {
 	lamp->dist = distance;
 	lamp->att1 = att1;
 	lamp->att2 = att2;
+	lamp->coeff_const = coeff_const;
+	lamp->coeff_lin = coeff_lin;
+	lamp->coeff_quad = coeff_quad;
 }
 
 void GPU_lamp_update_spot(GPULamp *lamp, float spotsize, float spotblend)
@@ -2254,6 +2265,9 @@ static void gpu_lamp_from_blender(Scene *scene, Object *ob, Object *par, Lamp *l
 	lamp->falloff_type = la->falloff_type;
 	lamp->att1 = la->att1;
 	lamp->att2 = la->att2;
+	lamp->coeff_const = la->coeff_const;
+	lamp->coeff_lin = la->coeff_lin;
+	lamp->coeff_quad = la->coeff_quad;
 	lamp->curfalloff = la->curfalloff;
 
 	/* initshadowbuf */
diff --git a/source/blender/gpu/shaders/gpu_shader_material.glsl b/source/blender/gpu/shaders/gpu_shader_material.glsl
index 51d4706d91e..05853c3e2d3 100644
--- a/source/blender/gpu/shaders/gpu_shader_material.glsl
+++ b/source/blender/gpu/shaders/gpu_shader_material.glsl
@@ -1627,6 +1627,17 @@ void lamp_falloff_sliders(float lampdist, float ld1, float ld2, float dist, out
 	visifac *= lampdistkw/(lampdistkw + ld2*dist*dist);
 }
 
+void lamp_falloff_invcoefficients(float coeff_const, float coeff_lin, float coeff_quad, float dist, out float visifac)
+{
+	vec3 coeff = vec3(coeff_const, coeff_lin, coeff_quad);
+	vec3 d_coeff = vec3(1.0, dist, dist*dist);
+	float visifac_r = dot(coeff, d_coeff);
+	if (visifac_r > 0.0)
+		visifac = 1.0 / visifac_r;
+	else
+		visifac = 0.0;
+}
+
 void lamp_falloff_curve(float lampdist, sampler2D curvemap, float dist, out float visifac)
 {
 	visifac = texture2D(curvemap, vec2(dist/lampdist, 0.0)).x;