Cycles: add offscreen dicing scale and dicing camera.

The offscreen dicing scale helps to significantly reduce memory usage,
by reducing the dicing rate for objects the further they are outside of
the camera view.

The dicing camera can be specified now, to keep the geometry fixed and
avoid crawling artifacts in animation. It is also useful for debugging,
to see the tesselation from a different camera location.

Differential Revision: https://developer.blender.org/D2891

4 files changed, 100 insertions, 3 deletions

diff --git a/intern/cycles/render/camera.cpp b/intern/cycles/render/camera.cpp
index 9b226140f08..b6757d80afd 100644
--- a/intern/cycles/render/camera.cpp
+++ b/intern/cycles/render/camera.cpp
@@ -128,6 +128,8 @@ NODE_DEFINE(Camera)
 	SOCKET_FLOAT(border.bottom, "Border Bottom", 0);
 	SOCKET_FLOAT(border.top, "Border Top", 0);
 
+	SOCKET_FLOAT(offscreen_dicing_scale, "Offscreen Dicing Scale", 1.0f);
+
 	return type;
 }
 
@@ -273,6 +275,13 @@ void Camera::update()
 	full_dx = transform_direction(&cameratoworld, full_dx);
 	full_dy = transform_direction(&cameratoworld, full_dy);
 
+	if(type == CAMERA_PERSPECTIVE) {
+		float3 v = transform_perspective(&full_rastertocamera, make_float3(full_width, full_height, 1.0f));
+
+		frustum_right_normal = normalize(make_float3(v.z, 0.0f, -v.x));
+		frustum_top_normal = normalize(make_float3(0.0f, v.z, -v.y));
+	}
+
 	/* TODO(sergey): Support other types of camera. */
 	if(type == CAMERA_PERSPECTIVE) {
 		/* TODO(sergey): Move to an utility function and de-duplicate with
@@ -581,8 +590,27 @@ BoundBox Camera::viewplane_bounds_get()
 
 float Camera::world_to_raster_size(float3 P)
 {
+	float res = 1.0f;
+
 	if(type == CAMERA_ORTHOGRAPHIC) {
-		return min(len(full_dx), len(full_dy));
+		res = min(len(full_dx), len(full_dy));
+
+		if(offscreen_dicing_scale > 1.0f) {
+			float3 p = transform_perspective(&worldtocamera, P);
+			float3 v = transform_perspective(&rastertocamera, make_float3(width, height, 0.0f));
+
+			/* Create point clamped to frustum */
+			float3 c;
+			c.x = max(-v.x, min(v.x, p.x));
+			c.y = max(-v.y, min(v.y, p.y));
+			c.z = max(0.0f, p.z);
+
+			float f_dist = len(p - c) / sqrtf((v.x*v.x+v.y*v.y)*0.5f);
+
+			if(f_dist > 0.0f) {
+				res += res * f_dist * (offscreen_dicing_scale - 1.0f);
+			}
+		}
 	}
 	else if(type == CAMERA_PERSPECTIVE) {
 		/* Calculate as if point is directly ahead of the camera. */
@@ -597,14 +625,74 @@ float Camera::world_to_raster_size(float3 P)
 		/* dPdx */
 		float dist = len(transform_point(&worldtocamera, P));
 		float3 D = normalize(Ddiff);
-		return len(dist*dDdx - dot(dist*dDdx, D)*D);
+		res = len(dist*dDdx - dot(dist*dDdx, D)*D);
+
+		/* Decent approx distance to frustum (doesn't handle corners correctly, but not that big of a deal) */
+		float f_dist = 0.0f;
+
+		if(offscreen_dicing_scale > 1.0f) {
+			float3 p = transform_point(&worldtocamera, P);
+
+			/* Distance from the four planes */
+			float r = dot(p, frustum_right_normal);
+			float t = dot(p, frustum_top_normal);
+			p = make_float3(-p.x, -p.y, p.z);
+			float l = dot(p, frustum_right_normal);
+			float b = dot(p, frustum_top_normal);
+			p = make_float3(-p.x, -p.y, p.z);
+
+			if(r <= 0.0f && l <= 0.0f && t <= 0.0f && b <= 0.0f) {
+				/* Point is inside frustum */
+				f_dist = 0.0f;
+			}
+			else if(r > 0.0f && l > 0.0f && t > 0.0f && b > 0.0f) {
+				/* Point is behind frustum */
+				f_dist = len(p);
+			}
+			else {
+				/* Point may be behind or off to the side, need to check */
+				float3 along_right = make_float3(-frustum_right_normal.z, 0.0f, frustum_right_normal.x);
+				float3 along_left = make_float3(frustum_right_normal.z, 0.0f, frustum_right_normal.x);
+				float3 along_top = make_float3(0.0f, -frustum_top_normal.z, frustum_top_normal.y);
+				float3 along_bottom = make_float3(0.0f, frustum_top_normal.z, frustum_top_normal.y);
+
+				float dist[] = {r, l, t, b};
+				float3 along[] = {along_right, along_left, along_top, along_bottom};
+
+				bool test_o = false;
+
+				float *d = dist;
+				float3 *a = along;
+				for(int i = 0; i < 4; i++, d++, a++) {
+					/* Test if we should check this side at all */
+					if(*d > 0.0f) {
+						if(dot(p, *a) >= 0.0f) {
+							/* We are in front of the back edge of this side of the frustum */
+							f_dist = max(f_dist, *d);
+						}
+						else {
+							/* Possibly far enough behind the frustum to use distance to origin instead of edge */
+							test_o = true;
+						}
+					}
+				}
+
+				if(test_o) {
+					f_dist = (f_dist > 0) ? min(f_dist, len(p)) : len(p);
+				}
+			}
+
+			if(f_dist > 0.0f) {
+				res += len(dDdx - dot(dDdx, D)*D) * f_dist * (offscreen_dicing_scale - 1.0f);
+			}
+		}
 	}
 	else {
 		// TODO(mai): implement for CAMERA_PANORAMA
 		assert(!"pixel width calculation for panoramic projection not implemented yet");
 	}
 
-	return 1.0f;
+	return res;
 }
 
 CCL_NAMESPACE_END
diff --git a/intern/cycles/render/camera.h b/intern/cycles/render/camera.h
index dd6b831b347..12d67044d4f 100644
--- a/intern/cycles/render/camera.h
+++ b/intern/cycles/render/camera.h
@@ -129,6 +129,8 @@ public:
 	BoundBox2D viewplane;
 	/* width and height change during preview, so we need these for calculating dice rates. */
 	int full_width, full_height;
+	/* controls how fast the dicing rate falls off for geometry out side of view */
+	float offscreen_dicing_scale;
 
 	/* border */
 	BoundBox2D border;
@@ -163,6 +165,9 @@ public:
 	float3 full_dx;
 	float3 full_dy;
 
+	float3 frustum_right_normal;
+	float3 frustum_top_normal;
+
 	/* update */
 	bool need_update;
 	bool need_device_update;
diff --git a/intern/cycles/render/scene.cpp b/intern/cycles/render/scene.cpp
index 260a325206c..8ab4dd48552 100644
--- a/intern/cycles/render/scene.cpp
+++ b/intern/cycles/render/scene.cpp
@@ -85,6 +85,7 @@ Scene::Scene(const SceneParams& params_, Device *device)
 	memset(&dscene.data, 0, sizeof(dscene.data));
 
 	camera = new Camera();
+	dicing_camera = new Camera();
 	lookup_tables = new LookupTables();
 	film = new Film();
 	background = new Background();
@@ -155,6 +156,7 @@ void Scene::free_memory(bool final)
 	if(final) {
 		delete lookup_tables;
 		delete camera;
+		delete dicing_camera;
 		delete film;
 		delete background;
 		delete integrator;
@@ -359,6 +361,7 @@ void Scene::reset()
 
 	/* ensure all objects are updated */
 	camera->tag_update();
+	dicing_camera->tag_update();
 	film->tag_update(this);
 	background->tag_update(this);
 	integrator->tag_update(this);
diff --git a/intern/cycles/render/scene.h b/intern/cycles/render/scene.h
index 204c38e5963..81b00b922e5 100644
--- a/intern/cycles/render/scene.h
+++ b/intern/cycles/render/scene.h
@@ -165,6 +165,7 @@ class Scene {
 public:
 	/* data */
 	Camera *camera;
+	Camera *dicing_camera;
 	LookupTables *lookup_tables;
 	Film *film;
 	Background *background;