While testing the solution of MDL-62319, I detected that within the assignment grading interface, dragging existing annotations might be stuttering and sluggish.

There are two things which might be improved. Both are not related directly, but should probably be tackled together.

Prerequisites:

• Use an iOS device (I can't tell if this problem is also happening on non-iOS devices)

• Login as teacher
• Create an assignment

• Login as student
• Open the assignment
• Submit a PDF file as solution

Test 1:

• Login as teacher again
• Open the assignment
• Open the assignment grading interface
• Create some annotations of various types (stamps, rectangles, and so on)
• Enable the "drag" tool (which is represented by the arrow button)
• Try to drag the existing annotations around on the canvas, by tapping on it to enable it and then dragging it to another location. Try especially to drag an annotation near and over the edge of the canvas and fetch it back to the middle of the canvas.

Expected result:

• Dragging the existing annotations always works smoothly, the annotation always follows your finger directly.

Actual result:

• Dragging the existing annotations does not always work. Sometimes, the annotation just follows the finger a few pixels and stops moving.

Test 2:

• Login as teacher again
• Open the assignment
• Open the assignment grading interface
• Create some annotations of various types (stamps, rectangles, and so on)
• Enable the "drag" tool (which is represented by the arrow button)
• Tap on an existing annotation A to enable it.
• Tap on another existing annotation B which is substantially far away from the currently enabled annotation A to drag it to another location.

Expected result:

• The interface will realize that you don't want to drag the enabled annotation A, it will automatically enable annotation B and move it as requested by the drag operation.

Actual result:

• The interface will not realize that you don't want to drag the enabled annotation A. Annotation A will jump to the location where you have started the drag operation and will then be moved as requested by the drag operation.