Blender Git Loki

Fix T81673: Color picker picks up UI and Overlay

There are two implementations of the Sample Color operation. One is used
by the paint texture and one by the image editor. The image editor
variant sampled from the ibuf directly, but the paint texture variant
was sampling from the screen front buffer. This can lead into incorrect
samples due to color pipeline.

This patch will use the image editor variant when sampling a color for
2d texture painting

Reviewed By: Pablo Dobarro

Differential Revision: https://developer.blender.org/D9408