[user-font] Implement subpixel-positioning

See:

https://github.com/harfbuzz/harfbuzz/pull/3411#issuecomment-1033118545
https://github.com/harfbuzz/harfbuzz/pull/3411#issuecomment-1033125311
https://github.com/harfbuzz/harfbuzz/pull/3411#issuecomment-1037765840

Basically the code in cairo-image-compositor.c:composite_glyphs()
is flooring glyph positions and putting some phase in the glyph-id.
This was being lost in the user-font backend. Fetch that and put it
in the recording-surface's device-transform translation, to be applied.

1 files changed, 92 insertions, 0 deletions

diff --git a/test/user-font-subpixel.c b/test/user-font-subpixel.c
new file mode 100644
index 000000000..5378c733f
--- /dev/null
+++ b/test/user-font-subpixel.c
@@ -0,0 +1,92 @@
+/*
+ * Copyright © 2022 Behdad Esfahbod
+ *
+ * Permission to use, copy, modify, distribute, and sell this software
+ * and its documentation for any purpose is hereby granted without
+ * fee, provided that the above copyright notice appear in all copies
+ * and that both that copyright notice and this permission notice
+ * appear in supporting documentation, and that the name of
+ * Red Hat, Inc. not be used in advertising or publicity pertaining to
+ * distribution of the software without specific, written prior
+ * permission. Red Hat, Inc. makes no representations about the
+ * suitability of this software for any purpose.  It is provided "as
+ * is" without express or implied warranty.
+ *
+ * RED HAT, INC. DISCLAIMS ALL WARRANTIES WITH REGARD TO THIS
+ * SOFTWARE, INCLUDING ALL IMPLIED WARRANTIES OF MERCHANTABILITY AND
+ * FITNESS, IN NO EVENT SHALL RED HAT, INC. BE LIABLE FOR ANY SPECIAL,
+ * INDIRECT OR CONSEQUENTIAL DAMAGES OR ANY DAMAGES WHATSOEVER
+ * RESULTING FROM LOSS OF USE, DATA OR PROFITS, WHETHER IN AN ACTION
+ * OF CONTRACT, NEGLIGENCE OR OTHER TORTIOUS ACTION, ARISING OUT OF OR
+ * IN CONNECTION WITH THE USE OR PERFORMANCE OF THIS SOFTWARE.
+ *
+ * Contributor(s):
+ *	Behdad Esfahbod <behdad@behdad.org>
+ */
+
+/* Test that user-fonts can subpixel positioning.
+ */
+
+#include "cairo-test.h"
+
+
+#define BORDER 10
+#define REPEAT 16
+#define TEXT_SIZE 24
+#define WIDTH  (TEXT_SIZE * REPEAT + 2*BORDER)
+#define HEIGHT (TEXT_SIZE + 2*BORDER)
+
+
+static cairo_status_t
+test_scaled_font_render_glyph (cairo_scaled_font_t  *scaled_font,
+			       unsigned long         glyph,
+			       cairo_t              *cr,
+			       cairo_text_extents_t *metrics)
+{
+    cairo_rectangle (cr, 0, .45, 1., .1);
+    cairo_fill (cr);
+    return CAIRO_STATUS_SUCCESS;
+}
+
+static cairo_font_face_t *
+_user_font_face_create (void)
+{
+    cairo_font_face_t *user_font_face;
+
+    user_font_face = cairo_user_font_face_create ();
+    cairo_user_font_face_set_render_glyph_func (user_font_face, test_scaled_font_render_glyph);
+
+    return user_font_face;
+}
+
+static cairo_test_status_t
+draw (cairo_t *cr, int width, int height)
+{
+    cairo_font_face_t *font_face;
+
+    cairo_set_source_rgb (cr, 1, 1, 1);
+    cairo_paint (cr);
+
+    font_face = _user_font_face_create ();
+
+    cairo_set_font_face (cr, font_face);
+    cairo_font_face_destroy (font_face);
+
+    cairo_set_source_rgb (cr, 0, 0, 0);
+    cairo_set_font_size (cr, TEXT_SIZE);
+
+    for (unsigned i = 0; i < REPEAT; i++)
+    {
+      cairo_move_to (cr, BORDER + TEXT_SIZE * i, BORDER + i * .1);
+      cairo_show_text (cr, "-");
+    }
+
+    return CAIRO_TEST_SUCCESS;
+}
+
+CAIRO_TEST (user_font_subpixel,
+	    "Tests user font subpixel rendering",
+	    "font, user-font", /* keywords */
+	    "cairo >= 1.17.4", /* requirements */
+	    WIDTH, HEIGHT,
+	    NULL, draw)