Bug 360760

It seems that picking color from canvas (ctrl+click/tap) is not working correctly while brush strokes are being processed. First of all, the little preview of selected color is showing black all the time (even if I drag the color picker across the whole canvas). Second, there is no effect of color picking, since I'm stuck with my initial color until instant preview finishes it works of transferring the pixel data to the full size image. After it has finished, everything works fine. 

It is possible to pick a color during processing but one needs to do it through a color selector.

Reproducible: Always

Steps to Reproduce:
1. Force long time instant preview processing (large canvas, with large brush size + some scribbles)
2. While  instant preview is processing pick a color from canvas (ctrl+mouse  click or ctrl+pen tap)


Actual Results:  
Result 1: Selected color is not being displayed correctly in color picking preview (while performing a drag)
Result 2: Color is not picked until instant preview finishes it's work

Expected Results:  
1. The preview of selected color ( while performing a drag) should display the correct color that is under the cursor.
2. The color selection should have an effect during the preview.

Potential solution suggestion: Pick colors from the additional small canvas that is being used to display instant preview. It wont be 100% accurate colors but at least there will be some responsiveness. Also correct and accurate colors are not needed during instant preview work (when we view the smaller size image), some approximation of final color will do just fine.

CPU: Intel i5-3210M @2.50 GHz 
Memory: 8 GB 
System: Windows 7 64b
GPU: NVIDIA GeForce GT 630M 
Tablet: Wacom Bamboo