API: map-to-image and create-similar-image

A common requirement is the fast upload of pixel data. In order to
allocate the most appropriate image buffer, we need knowledge of the
destination. The most obvious example is that we could use a
shared-memory region for the image to avoid the transfer cost of
uploading the pixels to the X server. Similarly, gl, win32, quartz...

The other side of the equation is that for manual modification of a
remote surface, it would be more efficient if we can create a similar
image to reduce the transfer costs. This strategy is already followed
for the destination fallbacks and this merely exposes the same
capability for the application fallbacks.

Signed-off-by: Chris Wilson <chris@chris-wilson.co.uk>

1 files changed, 36 insertions, 1 deletions

diff --git a/src/cairo-image-surface.c b/src/cairo-image-surface.c
index c14aac064..369f1728e 100644
--- a/src/cairo-image-surface.c
+++ b/src/cairo-image-surface.c
@@ -728,6 +728,36 @@ _cairo_image_surface_create_similar (void	       *abstract_other,
 						     width, height);
 }
 
+static cairo_surface_t *
+_cairo_image_surface_map_to_image (void *abstract_other,
+				   const cairo_rectangle_int_t *extents)
+{
+    cairo_image_surface_t *other = abstract_other;
+    cairo_surface_t *surface;
+    uint8_t *data;
+
+    data = other->data;
+    data += extents->y * other->stride;
+    data += extents->x * PIXMAN_FORMAT_BPP (other->pixman_format)/ 8;
+
+    surface =
+	_cairo_image_surface_create_with_pixman_format (data,
+							other->pixman_format,
+							extents->width,
+							extents->height,
+							other->stride);
+
+    cairo_surface_set_device_offset (surface, -extents->x, -extents->y);
+    return surface;
+}
+
+static cairo_int_status_t
+_cairo_image_surface_unmap_image (void *abstract_surface,
+				  cairo_image_surface_t *image)
+{
+    return CAIRO_INT_STATUS_SUCCESS;
+}
+
 static cairo_status_t
 _cairo_image_surface_finish (void *abstract_surface)
 {
@@ -4655,10 +4685,15 @@ _cairo_surface_is_image (const cairo_surface_t *surface)
 
 const cairo_surface_backend_t _cairo_image_surface_backend = {
     CAIRO_SURFACE_TYPE_IMAGE,
+    _cairo_image_surface_finish,
+
     _cairo_default_context_create,
 
     _cairo_image_surface_create_similar,
-    _cairo_image_surface_finish,
+    NULL, /* create similar image */
+    _cairo_image_surface_map_to_image,
+    _cairo_image_surface_unmap_image,
+
     _cairo_image_surface_acquire_source_image,
     _cairo_image_surface_release_source_image,
     _cairo_image_surface_acquire_dest_image,