[cairo] font rendering issue

Ciprian Cudalbu cudalbuc at yahoo.com
Fri Jul 19 19:17:12 UTC 2019

cairo version: cairo-1.16.0
hardware: Intel HD 530, Intel UHD 620 with latest open gl drivers (may 2019)
backend: opengl
api: cairo_show_text
input: string "ij", in size 33
 _cairo_scaled_font_glyph_device_extents detects that the glyphs overlap and rendering takes the mask path, render_glyphs_via_mask.
After doing the mask texture rendering it draws the mask texture into the frame buffer 0. It appears that on the intel driverthere is not synchronization and the texture is used before being ready. This causes garbled output for text and if a lot of text is drawn the gl backend no longer works.
A simple solution is to insert a glFlush just before  cairo_surface_destroy (mask). This takes care of the issue but I am not sure what it does in terms of performance.
I hope this info is useful.
Best regards,Ciprian Cudalbu.

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