Speak AT-SPI2 on the accessibility bus from the display, over Vega's own D-Bus

vega display --access joins the accessibility bus as AT-SPI2 objects for
screen readers such as Orca, with no toolkit, ATK or libdbus: dbus.c
speaks the D-Bus wire format (EXTERNAL authentication, headers, aligned
bodies, calls, replies, signals). The tree follows what the say surface
says: a heading, a label per field, a list box per list whose items know
their place and which is selected and focused, tables, the entry, the
keys as buttons; answers come from the app when asked, one object has the
focus, and focus moves are said as events. Assistive technology can act
too: Selection focuses a row, Action presses a key. The live loop now
draws only when something changed, so a screen reader's questions no
longer cost frames. The check walks the tree with gdbus on a private
session bus with at-spi-bus-launcher, and follows the focus through keys,
Selection, Action and the events.

1 files changed, 22 insertions, 0 deletions

diff --git a/surfaces/vega.h b/surfaces/vega.h
index cd6b1ee..9f30ee4 100644
--- a/surfaces/vega.h
+++ b/surfaces/vega.h
@@ -139,6 +139,28 @@ void vega_pixels(const VegaGrid *, VegaFace *, uint32_t *out, size_t stride);
 /* width x height of out in the background's colour. */
 void vega_pixels_clear(uint32_t *out, size_t stride, unsigned width, unsigned height);
 
+/* Accessibility on Linux desktops (access.c): the screen as AT-SPI2 objects
+ * on the accessibility bus, for screen readers. The surface that hosts it
+ * says whether the user is typing and what, presses keys for assistive
+ * technology, and hears when that changed the app. */
+typedef struct {
+    void *context;
+    bool (*typing)(void *);
+    const char *(*typed)(void *, size_t *length);
+    bool (*press)(void *, const char *key);
+    void (*changed)(void *);
+} VegaAccessHost;
+typedef struct VegaAccess VegaAccess;
+/* Join the accessibility bus; NULL (with why) when there is none. */
+VegaAccess *vega_access_open(PureApp *, const VegaScreen *, const VegaAccessHost *, char *error, size_t error_size);
+int vega_access_fd(const VegaAccess *);
+/* Answer what assistive technology asked (the fd is readable); false when
+ * the bus is gone. */
+bool vega_access_read(VegaAccess *);
+/* After the app changed: the focus that moved, as events. */
+void vega_access_changed(VegaAccess *);
+void vega_access_close(VegaAccess *);
+
 /* A display through KMS: the first connected connector (or, with writeback,
  * a writeback connector: the frames come back to memory, so no screen is
  * needed to check them), its preferred mode or width x height. */