[Bf-blender-cvs] [60030d1511b] cycles-x: Cycles-X: Change viewport update system to be time based rather than sample based on fast devices

[Alaska]

Commit: 60030d1511bd8e89bbca0e116d563ee1b8bd6674
Author: Alaska
Date:   Mon Aug 30 09:12:45 2021 +0200
Branches: cycles-x
https://developer.blender.org/rB60030d1511bd8e89bbca0e116d563ee1b8bd6674

Cycles-X: Change viewport update system to be time based rather than sample based on fast devices

The viewport update speed when rendering with infinite samples has been changed to work based primarily on time since render start rather than sample count.

This change has been made because if you have a device fast enough to exceed 32 samples in 0.1 seconds, then the next viewport update you'll observe is 2 seconds after `render start` which can be annoying for anyone wishing to quickly iterate on fine details as `render start` is usually a 1 sample per pixel image meaning fine detail is lost in noise or overly blurred by a denoiser.

This change was made possible with help from Will Rusthon (a friend) and Blender developers.

Here is an example video of the issue (some of the "viewport changes" you see are due to compression artifacts to keep the video small):
{F10290321}

And here is my fix tested (the second demo with the caustics is there to show that the viewport updates reduce as time goes on. It's easier to see in the caustics scene due to the fireflies. This is important because reduced viewpoint updates means faster ray tracing. The difference is that with this patch the slow viewport update (once every 2 seconds) has been moved to after rendering for 8 seconds rather than occurring at 32 samples which could happen really quickly with simplistic sce [...]
{F10290508}

Reviewed By: sergey, leesonw

Differential Revision: https://developer.blender.org/D12265

===================================================================

M	intern/cycles/integrator/render_scheduler.cpp
M	intern/cycles/integrator/render_scheduler.h

===================================================================

diff --git a/intern/cycles/integrator/render_scheduler.cpp b/intern/cycles/integrator/render_scheduler.cpp
index b33c2068dc9..af16e8a0c59 100644
--- a/intern/cycles/integrator/render_scheduler.cpp
+++ b/intern/cycles/integrator/render_scheduler.cpp
@@ -630,17 +630,22 @@ double RenderScheduler::guess_display_update_interval_in_seconds_for_num_samples
     }
     return 2.0;
   }
-
-  if (num_rendered_samples < 4) {
+  
+  /* Render time and number of samples rendered are used to figure out the display update interval.
+  *  Render time is used to allow for fast display updates in the first few seconds of rendering
+  *  on fast devices. Number of samples rendered is used to allow for potentially quicker display
+  *  updates on slow devices during the first few samples. */
+  const double render_time = path_trace_time_.get_wall();
+  if (render_time < 1) {
     return 0.1;
   }
-  if (num_rendered_samples < 8) {
+  if (render_time < 2) {
     return 0.25;
   }
-  if (num_rendered_samples < 16) {
+  if (render_time < 4) {
     return 0.5;
   }
-  if (num_rendered_samples < 32) {
+  if (render_time < 8 || num_rendered_samples < 32) {
     return 1.0;
   }
   return 2.0;
@@ -649,7 +654,7 @@ double RenderScheduler::guess_display_update_interval_in_seconds_for_num_samples
 int RenderScheduler::calculate_num_samples_per_update() const
 {
   const double time_per_sample_average = path_trace_time_.get_average();
-  const double num_samples_in_second = 1.0 / time_per_sample_average;
+  const double num_samples_in_second = pixel_size_ * pixel_size_ / time_per_sample_average;
 
   const double update_interval_in_seconds = guess_display_update_interval_in_seconds();
 
@@ -810,9 +815,10 @@ bool RenderScheduler::work_need_denoise(bool &delayed)
     return false;
   }
 
-  /* Avoid excessive denoising in viewport after reaching a certain amount of samples. */
+  /* Avoid excessive denoising in viewport after reaching a certain sample count and render time. */
   /* TODO(sergey): Consider making time interval and sample configurable. */
-  delayed = (num_samples_finished >= 20 && (time_dt() - state_.last_display_update_time) < 1.0);
+  delayed = (path_trace_time_.get_wall() > 4 && num_samples_finished >= 20 &&
+      (time_dt() - state_.last_display_update_time) < 1.0);
 
   return !delayed;
 }
diff --git a/intern/cycles/integrator/render_scheduler.h b/intern/cycles/integrator/render_scheduler.h
index dc354737f6f..c58bcb20089 100644
--- a/intern/cycles/integrator/render_scheduler.h
+++ b/intern/cycles/integrator/render_scheduler.h
@@ -192,8 +192,9 @@ class RenderScheduler {
   bool is_denoise_active_during_update() const;
 
   /* Heuristic which aims to give perceptually pleasant update of display interval in a way that at
-   * lower samples updates happens more often, but with higher number of samples updates happens
-   * less often but the device occupancy goes higher. */
+   * lower samples and near the beginning of rendering, updates happen more often, but with higher 
+   * number of samples and later in the render, updates happen less often but device occupancy
+   * goes higher. */
   double guess_display_update_interval_in_seconds() const;
   double guess_display_update_interval_in_seconds_for_num_samples(int num_rendered_samples) const;
   double guess_display_update_interval_in_seconds_for_num_samples_no_limit(