Created attachment 200782 [details]
example XPS document showing SolidColorBrush with opacity

Review of attachment 200781 [details] [review]:

Thanks for the patch, I have some small comments.

::: libgxps/gxps-page.c
@@ +1277,3 @@
 	if (strcmp (element_name, "SolidColorBrush") == 0) {
+		gdouble a, r, g, b;
+		const gchar *colorstr = NULL;

Use color_str instead.

@@ +1285,2 @@
 			} else if (strcmp (names[i], "Opacity") == 0) {
+				brush->opacity = g_ascii_strtod (values[i], NULL);

Use gxps_value_get_double() and fill error if returns FALSE.

@@ +1290,3 @@
 		}
+
+		if (colorstr && gxps_color_parse (colorstr, &a, &r, &g, &b)) {

Instead of this, we could modify gxps_create_solid_color_pattern() to receive a global alpha value or add a new method gxps_create_solid_color_pattern_with_alpha().

@@ +1293,3 @@
+			GXPS_DEBUG (g_message ("set_fill_pattern (solid)"));
+			a *= brush->opacity;
+			brush->pattern = (a != 1.0) ?

I've realized we don't need this, because cairo_pattern_create_rgb() calls cairo_pattern_create_rgba() with alpha = 1, so we can just use cairo_pattern_create_rgba() always.

Created attachment 201043 [details] [review]
adds Opacity support for SolidColorBrush elements

Review of attachment 201043 [details] [review]:

Great!, I've just pushed it to git master, with the modifications I comment below.

::: libgxps/gxps-page.c
@@ +975,3 @@
 		return NULL;
 
+	a *= alpha;

a i not used after this, so we can just call pattern = cairo_pattern_create_rgba (r, g, b, a * alpha);

@@ +1448,3 @@
 							  brush->ctx->page->priv->source,
 							  G_MARKUP_ERROR_INVALID_CONTENT,
+							  "Opacity", "SolidColorBrush",

I don't know why you changed it, because it was correct, it's element_name, attribute_name

@@ +1457,3 @@
 		}
+
+		if (color_str) {

Color is required, so we should fail with MISSING_ATTRIBUTE error if color is missing.

@@ +1466,3 @@
+					  brush->ctx->page->priv->source,
+					  G_MARKUP_ERROR_INVALID_CONTENT,
+					  "Color", "SolidColorBrush",

Same here, it's first the element_name

(In reply to comment #4)
> @@ +1448,3 @@
>                                brush->ctx->page->priv->source,
>                                G_MARKUP_ERROR_INVALID_CONTENT,
> +                              "Opacity", "SolidColorBrush",
> 
> I don't know why you changed it, because it was correct, it's element_name,
> attribute_name

I was going by the error messages I received from my test files. Example:

Error rendering page /Documents/1/Pages/1.fpage: /Documents/1/Pages/1.fpage:4:55 invalid content in attribute 'SolidColorBrush' of element 'Opacity': abc

See new bug https://bugzilla.gnome.org/show_bug.cgi?id=663899