Cycles: Implement rolling shutter effect

This is an attempt to emulate real CMOS cameras which reads sensor by scanlines
and hence different scanlines are sampled at a different moment in time, which
causes so called rolling shutter effect. This effect will, for example, make
vertical straight lines being curved when doing horizontal camera pan.

This is controlled by the Shutter Type option in the Motion Blur panel.

Additionally, since scanline sampling is not instantaneous it's possible to have
motion blur on top of rolling shutter.

This is controlled by the Rolling Shutter Time slider which controls balance
between pure rolling shutter effect and pure motion blur effect.

Reviewers: brecht, juicyfruit, dingto, keir

Differential Revision: https://developer.blender.org/D1624

1 files changed, 29 insertions, 0 deletions

diff --git a/intern/cycles/kernel/kernel_camera.h b/intern/cycles/kernel/kernel_camera.h
index 01017eabde2..c51174b645d 100644
--- a/intern/cycles/kernel/kernel_camera.h
+++ b/intern/cycles/kernel/kernel_camera.h
@@ -294,8 +294,37 @@ ccl_device void camera_sample(KernelGlobals *kg, int x, int y, float filter_u, f
 		ray->time = TIME_INVALID;
 	}
 	else {
+		/* TODO(sergey): Such lookup is unneeded when there's rolling shutter
+		 * effect in use but rollign shutter duration is set to 0.0.
+		 */
 		const int shutter_table_offset = kernel_data.cam.shutter_table_offset;
 		ray->time = lookup_table_read(kg, time, shutter_table_offset, SHUTTER_TABLE_SIZE);
+		/* TODO(sergey): Currently single rolling shutter effect type only
+		 * where scanlines are acquired from top to bottom and whole scanline
+		 * is acquired at once (no delay in acquisition happens between pixels
+		 * of sinle scanline).
+		 *
+		 * Might want to support more models in the future.
+		 */
+		if(kernel_data.cam.rolling_shutter_type) {
+			/* Time corresponding to a fully rolling shutter only effect:
+			 * top of the frame is time 0.0, bottom of the frame is time 1.0.
+			 */
+			const float time = 1.0f - (float)y / kernel_data.cam.height;
+			const float duration = kernel_data.cam.rolling_shutter_duration;
+			if(duration != 0.0f) {
+				/* This isn't fully physical correct, but lets us to have simple
+				 * controls in the interface. The idea here is basically sort of
+				 * linear interpolation between how much rolling shutter effect
+				 * exist on the frame and how much of it is a motion blur effect.
+				 */
+				ray->time = (ray->time - 0.5f) * duration;
+				ray->time += (time - 0.5f) * (1.0f - duration) + 0.5f;
+			}
+			else {
+				ray->time = time;
+			}
+		}
 	}
 #endif