[cairo] [patch] gl: do not force flush everytime uploading a glyph image to glyph cache

[Zhigang Gong]

> -----Original Message-----
> From: cairo-bounces+zhigang.gong=linux.intel.com at cairographics.org
> [mailto:cairo-bounces+zhigang.gong=linux.intel.com at cairographics.org]
> On Behalf Of Eric Anholt
> Sent: Wednesday, January 30, 2013 10:51 AM
> To: Henry (Yu) Song - SISA; cairo at cairographics.org
> Subject: Re: [cairo] [patch] gl: do not force flush everytime uploading a
> glyph image to glyph cache
> 
> "Henry (Yu) Song - SISA" <hsong at sisa.samsung.com> writes:
> 
> > Hi, Eric
> >
> > Thanks for review and comment.  I will reformat the message.
> >
> > Each glyph uploading causes a flush of previous glDrawXXX().  A single
> > glyph uploading is done by _cairo_gl_surface_draw_image(), in which
> > _cairo_gl_composite_flush() is called.
> >
> > If I understand correctly, the question is how to ensure all glyph
> > drawings are flushed before we start draw something else.  correct me
> > if I am wrong.
> >
> > _cairo_gl_composite_flush () is called in multiple points, for example
> > when mask surface has changed.  In glyph rendering, we uses two
> > particular mask surface - one is the glyph cache that stores
> > alpha-only glyphs, the second one is the rgba-glyph cache that stores
> > lcd/subpixel images.  It is ensured all glyphs will be glDraw() before
> > we switch to draw something else in _cairo_gl_operand_needs_setup(),
> > where it checks the new mask vs the ctx->mask.
> 
> From what I can see, add_glyph is inside of the loop rendering glyphs to
> the temp mask.  I want to know how the rendering of former glyphs to
> the
> into the temp mask gets flushed when a new glyph is being put into the
> glyph cache that may overwrite a previous glyph.
>From my point of view, cairo glyphs cache algorithm will not evict a used
cached glyph, so this may not be an issue. The corresponding code snippet
is as below:
@function:_cairo_gl_glyph_cache_add_glyph.

    /* search for an available slot */
    status = _cairo_rtree_insert (&cache->rtree, width, height, &node);
    /* search for an unlocked slot */
    if (status == CAIRO_INT_STATUS_UNSUPPORTED) {
        status = _cairo_rtree_evict_random (&cache->rtree,
                                            width, height, &node);
        if (status == CAIRO_INT_STATUS_SUCCESS) {
            status = _cairo_rtree_node_insert (&cache->rtree,
                                               node, width, height, &node);
        }
    }