Problem with fg accuracy and render vertex color results
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You are generating vertex colours (using RenderMap-Sampling-Vertices only), but with a twist, as the scene also uses a Final Gathering rendering effect. You then decide to increase the FG-accuracy to a very high level, and render the scene with the Render region, which renders fine and displays the desired results as expected. But, as soon as the Render region is disabled, the FG result in OGL display mode shows a poor quality result. Any attempts to re-generate the vertex colours produces a matte black surface. What can be the cause of this behavior.
After regenerating the vertex map
The Final Gathering process will only cache FG samples for visible surfaces (i.e. visible from the active scene camera). Since the Render vertex map process uses a virtual camera to render the surface to an image file, there is no automated process that will update the FG result after each update, which will require some manual intervention in order to make things work. In other words, what is occurring, is that after increasing the FG accuracy level to 500, then regenerating the vertex map, the Render vertex colors process will look-up the FG image file that was previously built, at a lower accuracy. Thus the unchanged lower quality FG result when viewed in OGL mode. To compound the situation, any attempts to re-draw a Render region in the camera viewport, and regenerating a new vertex map, will produce the matte black surface result.
The key to solving this enigma, is to use the Render region to generate the FG map, but to source the FG map from the Final Gathering Map of the Render-Options PPG (and NOT the Render region PPG). Follow this recipe to workaround the problem :
1) First thing to do is to open the Render-Region-Options PPG, make sure the FG box is checked, most importantly turn off the Rebuild parameter, and give a new FGmap filename (optional: pointing the FGmap in a new path if need be).
2) Draw a Render region in the camera viewport, and wait until the render process has terminated; a new FGmap has been created.
3) Now, open the Render-Render-Options PPG, activate Final Gathering, make sure the FGmap path points to the newly created FGmap file, and insure that the Rebuild parameter is unchecked (NOT active). At this point of the game, you do not want to overwrite the FGmap file.
4) It is recommended to remove the existing UV_Cluster_auto node associated with the target object (in this case study, a Grid), and then define a new Rendermap property for the Grid.
5) Open the Rendermap PPG, change the sampling to Vertices only, and add a new vertex_color for the object.
6) Go back to the Render-Render-Options PPG, and increase the FG accuracy value to a very high level; in this case study, 500 was used. You might want to experiment with much much higher values for better quality results. Beware though, as the Render vertex generation process will take enormous amounts of time the higher the FG accuracy value, especially in the case of objects containing large numbers of vertices, as these all the vertices will have to be evaluated.
7) Now, go back to the Rendermap PPG, and generate the vertex map (Regenerate map button); as mentioned in step 6, this might take a long time to process depending on the object