[gtk/small-text-fixes] gsk: Avoid cut-off glyphs with large scales

[Matthias Clasen <matthiasc src gnome org>]

commit 46a8f4d67e1a2893936a48f95062989faccda3ed
Author: Matthias Clasen <mclasen redhat com>
Date:   Tue Aug 31 23:04:14 2021 -0400

    gsk: Avoid cut-off glyphs with large scales
    
    With large scales, I could observe the bottoms
    of glyphs getting cut off on their way into the
    glyph cache. Avoid that by adjusting their position.

 gsk/ngl/gsknglglyphlibrary.c | 14 ++++++++++++--
 1 file changed, 12 insertions(+), 2 deletions(-)
---
diff --git a/gsk/ngl/gsknglglyphlibrary.c b/gsk/ngl/gsknglglyphlibrary.c
index 0fe94e05a5..4a29ecbae4 100644
--- a/gsk/ngl/gsknglglyphlibrary.c
+++ b/gsk/ngl/gsknglglyphlibrary.c
@@ -162,11 +162,13 @@ static void
 render_glyph (cairo_surface_t           *surface,
               const cairo_scaled_font_t *scaled_font,
               const GskNglGlyphKey      *key,
-              const GskNglGlyphValue    *value)
+              const GskNglGlyphValue    *value,
+              double                     device_scale)
 {
   cairo_t *cr;
   cairo_glyph_t glyph;
   cairo_font_options_t *options;
+  cairo_text_extents_t extents;
 
   g_assert (surface != NULL);
   g_assert (scaled_font != NULL);
@@ -186,6 +188,14 @@ render_glyph (cairo_surface_t           *surface,
   glyph.x = 0.25 * key->xshift - value->ink_rect.x;
   glyph.y = 0.25 * key->yshift - value->ink_rect.y;
 
+  cairo_glyph_extents (cr, &glyph, 1, &extents);
+
+  /* FIXME: this should not happen. But it does, with large text sizes. */
+  if (cairo_image_surface_get_width (surface)/device_scale < glyph.x + extents.x_bearing + extents.width)
+    glyph.x = cairo_image_surface_get_width (surface)/device_scale - extents.width - extents.x_bearing;
+  if (cairo_image_surface_get_height (surface)/device_scale < glyph.y + extents.y_bearing + extents.height)
+    glyph.y = cairo_image_surface_get_height (surface)/device_scale - extents.height - extents.y_bearing;
+
   cairo_show_glyphs (cr, &glyph, 1);
   cairo_destroy (cr);
 
@@ -229,7 +239,7 @@ gsk_ngl_glyph_library_upload_glyph (GskNglGlyphLibrary     *self,
                                           key->glyph);
 
   surface = gsk_ngl_glyph_library_create_surface (self, stride, width, height, device_scale);
-  render_glyph (surface, scaled_font, key, value);
+  render_glyph (surface, scaled_font, key, value, device_scale);
 
   texture_id = GSK_NGL_TEXTURE_ATLAS_ENTRY_TEXTURE (value);