Cycles: adaptive subdivision support for panoramic cameras.

Adds the code to get screen size of a point in world space, which is
used for subdividing geometry to the correct level. The approximate
method of treating the point as if it were directly in front of the
camera is used, as panoramic projections can become very distorted
near the edges of an image. This should be fine for most uses.

There is also no support yet for offscreen dicing scale, though
panorama cameras are often used for rendering 360° renders anyway.

Fixes T49254.

Differential Revision: https://developer.blender.org/D2468

1 files changed, 36 insertions, 3 deletions

diff --git a/intern/cycles/render/camera.cpp b/intern/cycles/render/camera.cpp
index 8b975886081..a2fda12ec85 100644
--- a/intern/cycles/render/camera.cpp
+++ b/intern/cycles/render/camera.cpp
@@ -27,6 +27,15 @@
 #include "util/util_math_cdf.h"
 #include "util/util_vector.h"
 
+/* needed for calculating differentials */
+#include "kernel/kernel_compat_cpu.h"
+#include "kernel/split/kernel_split_data.h"
+#include "kernel/kernel_globals.h"
+#include "kernel/kernel_projection.h"
+#include "kernel/kernel_differential.h"
+#include "kernel/kernel_montecarlo.h"
+#include "kernel/kernel_camera.h"
+
 CCL_NAMESPACE_BEGIN
 
 static float shutter_curve_eval(float x,
@@ -688,9 +697,33 @@ float Camera::world_to_raster_size(float3 P)
 			}
 		}
 	}
-	else {
-		// TODO(mai): implement for CAMERA_PANORAMA
-		assert(!"pixel width calculation for panoramic projection not implemented yet");
+	else if(type == CAMERA_PANORAMA) {
+		float3 D = transform_point(&worldtocamera, P);
+		float dist = len(D);
+
+		Ray ray;
+
+		/* Distortion can become so great that the results become meaningless, there
+		 * may be a better way to do this, but calculating differentials from the
+		 * point directly ahead seems to produce good enough results. */
+#if 0
+		float2 dir = direction_to_panorama(&kernel_camera, normalize(D));
+		float3 raster = transform_perspective(&cameratoraster, make_float3(dir.x, dir.y, 0.0f));
+
+		ray.t = 1.0f;
+		camera_sample_panorama(&kernel_camera, raster.x, raster.y, 0.0f, 0.0f, &ray);
+		if(ray.t == 0.0f) {
+			/* No differentials, just use from directly ahead. */
+			camera_sample_panorama(&kernel_camera, 0.5f*width, 0.5f*height, 0.0f, 0.0f, &ray);
+		}
+#else
+		camera_sample_panorama(&kernel_camera, 0.5f*width, 0.5f*height, 0.0f, 0.0f, &ray);
+#endif
+
+		differential_transfer(&ray.dP, ray.dP, ray.D, ray.dD, ray.D, dist);
+
+		return max(len(ray.dP.dx) * (float(width)/float(full_width)),
+		           len(ray.dP.dy) * (float(height)/float(full_height)));
 	}
 
 	return res;