This is NOT simply an awkward misfeature in the GUI, but a bug that results in Krita not being able to be used on OS X because the user cannot see what they are doing/working on in the canvas.

I am using Mac Yosemite 10.10.3. I downloaded my version of Krita (Beta 9.4) from http://files.kde.org/krita/osx/ and when I use Krita the canvas does not update at all. I tested with my tablet and tested simply by input from the track pad on my late 2013 MacBook Pro Retina, the outcome was the same, the canvas would not update the lines 1) while I was performing the drawing action and 2) after I finished my input. The overview panel displayed the updates to the drawing after the stroke/input had finished, as I would expect the overview panel to do. That test was with OpenGL on, Trilinear Filtering and texture buffer on.

I then continued on testing with OpenGL on and using all of the other scale modes and none worked. Texture buffering was on the whole time for the tests. I then test all of them again without texture buffering, this time the canvas did update but updated incredibly slow and only segments updated. The segments were tiles/blocked rectangular areas updating and only updated after I tried to draw on the spot, BUT it was updating information on the canvas previous to what I was currently drawing and not the current input/stroke.

By the way, OpenGl off equates to no pressure sensitivity from tablet input. My Huion K58 Tablet worked perfectly with Krita and my Mac before, and my Drivers are up to date. I do not know if this is to be expected, but I am stating it so you know.

Through all test overview panel updated as expected and has not apparent errors/bugs.

This makes Krita unable to be used and should be considered near high priority, if not the highest priority, on the Mac end. I say this because, with general use there is no critical crashes and this would then be the next important thing. Please note older versions worked as expected without any form of delay in the canvas on the default settings of OpenGL on, tri-filtering, and texture buffer on.

Reproducible: Always

Steps to Reproduce:
1.Open/create new document in mac version of Krita Beta (v2.8.93.0 - v2.9.4.5)
2. Put input (draw on tablet or w/ any other input device) into the canvas using the brush tool. [Make sure OpenGL is on w/ texture buffering as well.
3.After finishing input, check canvas and overview panel for updated content.

Actual Results:  
The canvas does not update with the new input/stroke either while the input/stroke is being completed or after the input/stroke is done. Overview updates after stroke finished, as expected.

Expected Results:  
As input/stroke is being drawn on canvas the content being drawn should appear in the updated canvas view fast enough that it appears as if one was actually making a stroke with a brush and should certainly stay visible on canvas afterwards.

Note: I have no idea what you mean by insert platform? I could not give any more information than what I knew, so in description I gave you my OS, and computer type, along with the Krita information.

The image provided is after I made a Stroke, used the Undo action, and then drew more. The content in the canvas appeared after the processing of the undo action, but the canvas did not update after I drew more with the brush tool in the canvas. You can see some of the rectangular blocks/tiles I mentioned before in the canvas view of the image. The black block appear when holding the cmd button on Mac.