Compositor: Display generated inputs in Viewers and Previews

Currently viewers and previews only display node trees that have at least one node with fixed resolution size. When all inputs are generated, nothing is displayed in most cases (RGB Node is displayed as a single pixel on previews). By generated I mean inputs not having resolution on their own, they create content dynamically given an output resolution.

This patch adds support for those cases by using an appropriate preferred resolution on Viewers/Previews which propagates to generated inputs as output resolution. Now:
- Viewers will display generated inputs with scene render resolution.
- Previews will display them with scene aspect ratio.
This is consistent with final render result and respects relative space.

The benefit for the user is being able to compose images without any input source. For example for creating mask images or simple backgrounds.

Reviewed By: Jeroen Bakker

Differential Revision: https://developer.blender.org/D10611

1 files changed, 3 insertions, 1 deletions

diff --git a/source/blender/compositor/intern/COM_NodeOperationBuilder.cc b/source/blender/compositor/intern/COM_NodeOperationBuilder.cc
index 818f2e4bcf6..1c741283c7b 100644
--- a/source/blender/compositor/intern/COM_NodeOperationBuilder.cc
+++ b/source/blender/compositor/intern/COM_NodeOperationBuilder.cc
@@ -195,7 +195,9 @@ PreviewOperation *NodeOperationBuilder::make_preview_operation() const
   bNodeInstanceHash *previews = m_context->getPreviewHash();
   if (previews) {
     PreviewOperation *operation = new PreviewOperation(m_context->getViewSettings(),
-                                                       m_context->getDisplaySettings());
+                                                       m_context->getDisplaySettings(),
+                                                       m_current_node->getbNode()->preview_xsize,
+                                                       m_current_node->getbNode()->preview_ysize);
     operation->setbNodeTree(m_context->getbNodeTree());
     operation->verifyPreview(previews, m_current_node->getInstanceKey());
     return operation;