Blender Internal is going to be removed in 2.8, so you can get now any type of error (I have found several in different areas not related to GP).

It looks the problem is on DRW_framebuffer_init() in GPENCIL_engine_init() https://developer.blender.org/diffusion/B/browse/greasepencil-object/source/blender/draw/engines/gpencil/gpencil_engine.c;b8df9f653178f356565d5beb8d7a979b2405420d$62

The change was committed to Blender 2.8 in daf02baaeaaf

Could you verify this is the function we talked about in IRC before commit the change?

@Dalai Felinto (dfelinto) In my previous comment I put the edit point funcytion, for the drawing while you move the mouse the function is gp_draw_stroke_buffer()

@Dalai Felinto (dfelinto) The drawing of the edit points is done in gp_draw_strokes_edit() function in drawgpencil.c. This function is caled from gp_draw_data_layers() for any datablock that is being edited (gpd->flag & GP_DATA_STROKE_EDITMODE)

@Dalai Felinto (dfelinto) My understanding is that this fix is only for sequencer.

@Clément Foucault (fclem) This is what we talked on IRC.

I type wrong the names: Credits to @Clément Foucault (fclem) and @Luca Rood (LucaRood) for the trick using the ProjectionMatrix to get the pixel size.

I forget to give credits for the icons to @Matias Mendiola (mendio) in the commit text, sorry for that.