Cycles: Pole merging for spherical stereo

The idea of pole merge is to fade interocular distance after a certain
altitude to zero when altitude goes closer to a pole. This should prevent
annoyances looking up in the sky or down to the bottom.

Works for both panorama and perspective cameras when Spherical Stereo
is enabled.

Reviewers: dfelinto, brecht

Reviewed By: brecht

Subscribers: sebastian_k

Differential Revision: https://developer.blender.org/D1998

5 files changed, 43 insertions, 2 deletions

diff --git a/intern/cycles/blender/blender_camera.cpp b/intern/cycles/blender/blender_camera.cpp
index 6b459ae575f..9dec489ce33 100644
--- a/intern/cycles/blender/blender_camera.cpp
+++ b/intern/cycles/blender/blender_camera.cpp
@@ -65,6 +65,9 @@ struct BlenderCamera {
 	bool use_spherical_stereo;
 	float interocular_distance;
 	float convergence_distance;
+	bool use_pole_merge;
+	float pole_merge_angle_from;
+	float pole_merge_angle_to;
 
 	enum { AUTO, HORIZONTAL, VERTICAL } sensor_fit;
 	float sensor_width;
@@ -183,6 +186,10 @@ static void blender_camera_from_object(BlenderCamera *bcam,
 		}
 		bcam->use_spherical_stereo = b_engine.use_spherical_stereo(b_ob);
 
+		bcam->use_pole_merge = b_camera.stereo().use_pole_merge();
+		bcam->pole_merge_angle_from = b_camera.stereo().pole_merge_angle_from();
+		bcam->pole_merge_angle_to = b_camera.stereo().pole_merge_angle_to();
+
 		bcam->ortho_scale = b_camera.ortho_scale();
 
 		bcam->lens = b_camera.lens();
@@ -427,6 +434,10 @@ static void blender_camera_sync(Camera *cam, BlenderCamera *bcam, int width, int
 			cam->stereo_eye = Camera::STEREO_NONE;
 	}
 
+	cam->use_pole_merge = bcam->use_pole_merge;
+	cam->pole_merge_angle_from = bcam->pole_merge_angle_from;
+	cam->pole_merge_angle_to = bcam->pole_merge_angle_to;
+
 	/* anamorphic lens bokeh */
 	cam->aperture_ratio = bcam->aperture_ratio;
 
diff --git a/intern/cycles/kernel/kernel_projection.h b/intern/cycles/kernel/kernel_projection.h
index c1a359e9269..8be6742699a 100644
--- a/intern/cycles/kernel/kernel_projection.h
+++ b/intern/cycles/kernel/kernel_projection.h
@@ -225,7 +225,7 @@ ccl_device float3 spherical_stereo_position(KernelGlobals *kg,
                                             float3 dir,
                                             float3 pos)
 {
-	const float interocular_offset = kernel_data.cam.interocular_offset;
+	float interocular_offset = kernel_data.cam.interocular_offset;
 
 	/* Interocular offset of zero means either non stereo, or stereo without
 	 * spherical stereo.
@@ -234,6 +234,21 @@ ccl_device float3 spherical_stereo_position(KernelGlobals *kg,
 		return pos;
 	}
 
+	if(kernel_data.cam.pole_merge_angle_to > 0.0f) {
+		float3 normalized_direction = normalize(dir);
+		const float pole_merge_angle_from = kernel_data.cam.pole_merge_angle_from,
+		            pole_merge_angle_to = kernel_data.cam.pole_merge_angle_to;
+		float altitude = fabsf(safe_asinf(normalized_direction.z));
+		if(altitude > pole_merge_angle_to) {
+			interocular_offset = 0.0f;
+		}
+		else if(altitude > pole_merge_angle_from) {
+			float fac = (altitude - pole_merge_angle_from) / (pole_merge_angle_to - pole_merge_angle_from);
+			float fade = cosf(fac * M_PI_2_F);
+			interocular_offset *= fade;
+		}
+	}
+
 	float3 up = make_float3(0.0f, 0.0f, 1.0f);
 	float3 side = normalize(cross(dir, up));
 
diff --git a/intern/cycles/kernel/kernel_types.h b/intern/cycles/kernel/kernel_types.h
index 02e69c7d75f..cc261ed37f8 100644
--- a/intern/cycles/kernel/kernel_types.h
+++ b/intern/cycles/kernel/kernel_types.h
@@ -909,9 +909,10 @@ typedef struct KernelCamera {
 	float4 equirectangular_range;
 
 	/* stereo */
-	int pad1, pad2;
 	float interocular_offset;
 	float convergence_distance;
+	float pole_merge_angle_from;
+	float pole_merge_angle_to;
 
 	/* matrices */
 	Transform cameratoworld;
diff --git a/intern/cycles/render/camera.cpp b/intern/cycles/render/camera.cpp
index ad96473e5d2..d992cac5312 100644
--- a/intern/cycles/render/camera.cpp
+++ b/intern/cycles/render/camera.cpp
@@ -76,6 +76,9 @@ Camera::Camera()
 	stereo_eye = STEREO_NONE;
 	interocular_distance = 0.065f;
 	convergence_distance = 30.0f * 0.065f;
+	use_pole_merge = false;
+	pole_merge_angle_from = 60.0f * M_PI_F / 180.0f;
+	pole_merge_angle_to = 75.0f * M_PI_F / 180.0f;
 
 	sensorwidth = 0.036f;
 	sensorheight = 0.024f;
@@ -367,6 +370,14 @@ void Camera::device_update(Device *device, DeviceScene *dscene, Scene *scene)
 	}
 
 	kcam->convergence_distance = convergence_distance;
+	if(use_pole_merge) {
+		kcam->pole_merge_angle_from = pole_merge_angle_from;
+		kcam->pole_merge_angle_to = pole_merge_angle_to;
+	}
+	else {
+		kcam->pole_merge_angle_from = -1.0f;
+		kcam->pole_merge_angle_to = -1.0f;
+	}
 
 	/* sensor size */
 	kcam->sensorwidth = sensorwidth;
diff --git a/intern/cycles/render/camera.h b/intern/cycles/render/camera.h
index 684b4458dfc..57b9960e70b 100644
--- a/intern/cycles/render/camera.h
+++ b/intern/cycles/render/camera.h
@@ -104,6 +104,9 @@ public:
 	bool use_spherical_stereo;
 	float interocular_distance;
 	float convergence_distance;
+	bool use_pole_merge;
+	float pole_merge_angle_from;
+	float pole_merge_angle_to;
 
 	/* anamorphic lens bokeh */
 	float aperture_ratio;