XCB: Use consistent rounding modes for a1 rasterisation.

This ports commits 36b4b06 and 7ab9ce1 from the image backend to xcb. Look
there for an explanation of why this is correct, I only copied this over and the
test suite said it was good. :-)

This fixes unantialiased-shapes, a1-rasterisation-rectangles and
a1-rasterisation-triangles.

Signed-off-by: Uli Schlachter <psychon@znc.in>

src/cairo-xcb-surface-render.c

@@ -1489,10 +1489,10 @@ _render_fill_boxes (void			*abstract_dst,
 	int i, j;
 
 	for (i = j = 0; i < chunk->count; i++) {
-	    int x1 = _cairo_fixed_integer_round (chunk->base[i].p1.x);
-	    int y1 = _cairo_fixed_integer_round (chunk->base[i].p1.y);
-	    int x2 = _cairo_fixed_integer_round (chunk->base[i].p2.x);
-	    int y2 = _cairo_fixed_integer_round (chunk->base[i].p2.y);
+	    int x1 = _cairo_fixed_integer_round_down (chunk->base[i].p1.x);
+	    int y1 = _cairo_fixed_integer_round_down (chunk->base[i].p1.y);
+	    int x2 = _cairo_fixed_integer_round_down (chunk->base[i].p2.x);
+	    int y2 = _cairo_fixed_integer_round_down (chunk->base[i].p2.y);
 
 	    if (x2 > x1 && y2 > y1) {
 		xrects[j].x = x1;
@@ -1552,10 +1552,10 @@ _render_composite_boxes (cairo_xcb_surface_t	*dst,
 	    int i;
 
 	    for (i = 0; i < chunk->count; i++) {
-		int x = _cairo_fixed_integer_round (box[i].p1.x);
-		int y = _cairo_fixed_integer_round (box[i].p1.y);
-		int width  = _cairo_fixed_integer_round (box[i].p2.x) - x;
-		int height = _cairo_fixed_integer_round (box[i].p2.y) - y;
+		int x = _cairo_fixed_integer_round_down (box[i].p1.x);
+		int y = _cairo_fixed_integer_round_down (box[i].p1.y);
+		int width  = _cairo_fixed_integer_round_down (box[i].p2.x) - x;
+		int height = _cairo_fixed_integer_round_down (box[i].p2.y) - y;
 
 		if (width && height) {
 		    _cairo_xcb_connection_render_composite (dst->connection,
@@ -1580,10 +1580,10 @@ _render_composite_boxes (cairo_xcb_surface_t	*dst,
 	    int i;
 
 	    for (i = 0; i < chunk->count; i++) {
-		int x = _cairo_fixed_integer_round (box[i].p1.x);
-		int y = _cairo_fixed_integer_round (box[i].p1.y);
-		int width  = _cairo_fixed_integer_round (box[i].p2.x) - x;
-		int height = _cairo_fixed_integer_round (box[i].p2.y) - y;
+		int x = _cairo_fixed_integer_round_down (box[i].p1.x);
+		int y = _cairo_fixed_integer_round_down (box[i].p1.y);
+		int width  = _cairo_fixed_integer_round_down (box[i].p2.x) - x;
+		int height = _cairo_fixed_integer_round_down (box[i].p2.y) - y;
 
 		if (width && height) {
 		    _cairo_xcb_connection_render_composite (dst->connection,
@@ -2817,7 +2817,7 @@ _clip_and_composite_boxes (cairo_xcb_surface_t *dst,
 static cairo_bool_t
 _mono_edge_is_vertical (const cairo_line_t *line)
 {
-    return _cairo_fixed_integer_round (line->p1.x) == _cairo_fixed_integer_round (line->p2.x);
+    return _cairo_fixed_integer_round_down (line->p1.x) == _cairo_fixed_integer_round_down (line->p2.x);
 }
 
 static cairo_bool_t
@@ -2855,7 +2855,8 @@ _traps_are_pixel_aligned (cairo_traps_t *traps,
 
 static void
 _boxes_for_traps (cairo_boxes_t *boxes,
-		  cairo_traps_t *traps)
+		  cairo_traps_t *traps,
+		  cairo_antialias_t antialias)
 {
     int i;
 
@@ -2866,21 +2867,40 @@ _boxes_for_traps (cairo_boxes_t *boxes,
     boxes->chunks.count = traps->num_traps;
     boxes->chunks.size  = traps->num_traps;
 
-    for (i = 0; i < traps->num_traps; i++) {
-	cairo_fixed_t x1 = traps->traps[i].left.p1.x;
-	cairo_fixed_t x2 = traps->traps[i].right.p1.x;
-	cairo_fixed_t y1 = traps->traps[i].top;
-	cairo_fixed_t y2 = traps->traps[i].bottom;
-
-	boxes->chunks.base[i].p1.x = x1;
-	boxes->chunks.base[i].p1.y = y1;
-	boxes->chunks.base[i].p2.x = x2;
-	boxes->chunks.base[i].p2.y = y2;
-
-	if (boxes->is_pixel_aligned) {
-	    boxes->is_pixel_aligned =
-		_cairo_fixed_is_integer (x1) && _cairo_fixed_is_integer (y1) &&
-		_cairo_fixed_is_integer (x2) && _cairo_fixed_is_integer (y2);
+    if (antialias != CAIRO_ANTIALIAS_NONE) {
+	for (i = 0; i < traps->num_traps; i++) {
+	    /* Note the traps and boxes alias so we need to take the local copies first. */
+	    cairo_fixed_t x1 = traps->traps[i].left.p1.x;
+	    cairo_fixed_t x2 = traps->traps[i].right.p1.x;
+	    cairo_fixed_t y1 = traps->traps[i].top;
+	    cairo_fixed_t y2 = traps->traps[i].bottom;
+
+	    boxes->chunks.base[i].p1.x = x1;
+	    boxes->chunks.base[i].p1.y = y1;
+	    boxes->chunks.base[i].p2.x = x2;
+	    boxes->chunks.base[i].p2.y = y2;
+
+	    if (boxes->is_pixel_aligned) {
+		boxes->is_pixel_aligned =
+		    _cairo_fixed_is_integer (x1) && _cairo_fixed_is_integer (y1) &&
+		    _cairo_fixed_is_integer (x2) && _cairo_fixed_is_integer (y2);
+	    }
+	}
+    } else {
+	boxes->is_pixel_aligned = TRUE;
+
+	for (i = 0; i < traps->num_traps; i++) {
+	    /* Note the traps and boxes alias so we need to take the local copies first. */
+	    cairo_fixed_t x1 = traps->traps[i].left.p1.x;
+	    cairo_fixed_t x2 = traps->traps[i].right.p1.x;
+	    cairo_fixed_t y1 = traps->traps[i].top;
+	    cairo_fixed_t y2 = traps->traps[i].bottom;
+
+	    /* round down here to match Pixman's behavior when using traps. */
+	    boxes->chunks.base[i].p1.x = _cairo_fixed_round_down (x1);
+	    boxes->chunks.base[i].p1.y = _cairo_fixed_round_down (y1);
+	    boxes->chunks.base[i].p2.x = _cairo_fixed_round_down (x2);
+	    boxes->chunks.base[i].p2.y = _cairo_fixed_round_down (y2);
 	}
     }
 }
@@ -3316,7 +3336,7 @@ _cairo_xcb_surface_render_composite_polygon (cairo_xcb_surface_t *dst,
     {
 	cairo_boxes_t boxes;
 
-	_boxes_for_traps (&boxes, &traps.traps);
+	_boxes_for_traps (&boxes, &traps.traps, antialias);
 	status = _clip_and_composite_boxes (dst, op, source,
 					    &boxes, antialias,
 					    extents, clip);