Add basic print functionality

It seems to perform roughly equally in optimized builds.

fastiv-io.c

@@ -162,6 +162,9 @@ try_append_page(cairo_surface_t *surface, cairo_surface_t **result,
 
 // - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -
 
+// From libwebp, verified to exactly match [x * a / 255].
+#define PREMULTIPLY8(a, x) (((uint32_t) (x) * (uint32_t) (a) * 32897U) >> 23)
+
 static bool
 pull_passthrough(const wuffs_base__more_information *minfo,
 	wuffs_base__io_buffer *src, wuffs_base__io_buffer *dst, GError **error)
@@ -1375,12 +1378,11 @@ load_libheif_image(struct heif_image_handle *handle, GError **error)
 		for (int y = 0; y < h; y++) {
 			uint32_t *dstp = (uint32_t *) (dst + dst_stride * y);
 			for (int x = 0; x < w; x++) {
-				uint32_t pixel = dstp[x], a = pixel >> 24;
-				uint8_t r = pixel >> 16;
-				uint8_t g = pixel >> 8;
-				uint8_t b = pixel;
+				uint32_t argb = dstp[x], a = argb >> 24;
 				dstp[x] = a << 24 |
-					(r * a / 255) << 16 | (g * a / 255) << 8 | (b * a / 255);
+					PREMULTIPLY8(a, 0xFF & (argb >> 16)) << 16 |
+					PREMULTIPLY8(a, 0xFF & (argb >>  8)) <<  8 |
+					PREMULTIPLY8(a, 0xFF &  argb);
 			}
 		}
 	}
@@ -2361,9 +2363,9 @@ read_spng_thumbnail(
 		for (size_t i = size / sizeof *data; i--; ) {
 			const uint8_t *unit = (const uint8_t *) &data[i];
 			uint32_t a = unit[3],
-				b = unit[2] * a / 255,
-				g = unit[1] * a / 255,
-				r = unit[0] * a / 255;
+				b = PREMULTIPLY8(a, unit[2]),
+				g = PREMULTIPLY8(a, unit[1]),
+				r = PREMULTIPLY8(a, unit[0]);
 			data[i] = a << 24 | r << 16 | g << 8 | b;
 		}
 	} else {

fastiv-view.c

@@ -165,6 +165,46 @@ get_display_dimensions(FastivView *self, int *width, int *height)
 	*height = ceil(h * self->scale);
 }
 
+static cairo_matrix_t
+get_orientation_matrix(FastivIoOrientation o, double width, double height)
+{
+	cairo_matrix_t matrix = {};
+	cairo_matrix_init_identity(&matrix);
+	switch (o) {
+	case FastivIoOrientation90:
+		cairo_matrix_rotate(&matrix, -M_PI_2);
+		cairo_matrix_translate(&matrix, -width, 0);
+		break;
+	case FastivIoOrientation180:
+		cairo_matrix_scale(&matrix, -1, -1);
+		cairo_matrix_translate(&matrix, -width, -height);
+		break;
+	case FastivIoOrientation270:
+		cairo_matrix_rotate(&matrix, +M_PI_2);
+		cairo_matrix_translate(&matrix, 0, -height);
+		break;
+	case FastivIoOrientationMirror0:
+		cairo_matrix_scale(&matrix, -1, +1);
+		cairo_matrix_translate(&matrix, -width, 0);
+		break;
+	case FastivIoOrientationMirror90:
+		cairo_matrix_rotate(&matrix, +M_PI_2);
+		cairo_matrix_scale(&matrix, -1, +1);
+		cairo_matrix_translate(&matrix, -width, -height);
+		break;
+	case FastivIoOrientationMirror180:
+		cairo_matrix_scale(&matrix, +1, -1);
+		cairo_matrix_translate(&matrix, 0, -height);
+		break;
+	case FastivIoOrientationMirror270:
+		cairo_matrix_rotate(&matrix, -M_PI_2);
+		cairo_matrix_scale(&matrix, -1, +1);
+	default:
+		break;
+	}
+	return matrix;
+}
+
 static void
 fastiv_view_get_preferred_height(
 	GtkWidget *widget, gint *minimum, gint *natural)
@@ -320,41 +360,7 @@ fastiv_view_draw(GtkWidget *widget, cairo_t *cr)
 	cairo_scale(cr, self->scale, self->scale);
 	cairo_set_source_surface(cr, self->frame, 0, 0);
 
-	cairo_matrix_t matrix = {};
-	cairo_matrix_init_identity(&matrix);
-	switch (self->orientation) {
-	case FastivIoOrientation90:
-		cairo_matrix_rotate(&matrix, -M_PI_2);
-		cairo_matrix_translate(&matrix, -sw, 0);
-		break;
-	case FastivIoOrientation180:
-		cairo_matrix_scale(&matrix, -1, -1);
-		cairo_matrix_translate(&matrix, -sw, -sh);
-		break;
-	case FastivIoOrientation270:
-		cairo_matrix_rotate(&matrix, +M_PI_2);
-		cairo_matrix_translate(&matrix, 0, -sh);
-		break;
-	case FastivIoOrientationMirror0:
-		cairo_matrix_scale(&matrix, -1, +1);
-		cairo_matrix_translate(&matrix, -sw, 0);
-		break;
-	case FastivIoOrientationMirror90:
-		cairo_matrix_rotate(&matrix, +M_PI_2);
-		cairo_matrix_scale(&matrix, -1, +1);
-		cairo_matrix_translate(&matrix, -sw, -sh);
-		break;
-	case FastivIoOrientationMirror180:
-		cairo_matrix_scale(&matrix, +1, -1);
-		cairo_matrix_translate(&matrix, 0, -sh);
-		break;
-	case FastivIoOrientationMirror270:
-		cairo_matrix_rotate(&matrix, -M_PI_2);
-		cairo_matrix_scale(&matrix, -1, +1);
-	default:
-		break;
-	}
-
+	cairo_matrix_t matrix = get_orientation_matrix(self->orientation, sw, sh);
 	cairo_pattern_t *pattern = cairo_get_source(cr);
 	cairo_pattern_set_matrix(pattern, &matrix);
 	cairo_pattern_set_extend(pattern, CAIRO_EXTEND_PAD);
@@ -563,18 +569,78 @@ show_error_dialog(GtkWindow *parent, GError *error)
 	g_error_free(error);
 }
 
+static GtkWindow *
+get_toplevel(GtkWidget *widget)
+{
+	if (GTK_IS_WINDOW((widget = gtk_widget_get_toplevel(widget))))
+		return GTK_WINDOW(widget);
+	return NULL;
+}
+
+static void
+on_draw_page(G_GNUC_UNUSED GtkPrintOperation *operation,
+	GtkPrintContext *context, G_GNUC_UNUSED int page_nr, FastivView *self)
+{
+	double surface_width_px = 0, surface_height_px = 0;
+	get_surface_dimensions(self, &surface_width_px, &surface_height_px);
+
+	// Any DPI will be wrong, unless we import that information from the image.
+	double scale = 1 / 96.;
+	double w = surface_width_px * scale, h = surface_height_px * scale;
+
+	// Scale down to fit the print area, taking care to not divide by zero.
+	double areaw = gtk_print_context_get_width(context);
+	double areah = gtk_print_context_get_height(context);
+	scale *= fmin((areaw < w) ? areaw / w : 1, (areah < h) ? areah / h : 1);
+
+	cairo_t *cr = gtk_print_context_get_cairo_context(context);
+	cairo_scale(cr, scale, scale);
+	cairo_set_source_surface(cr, self->frame, 0, 0);
+	cairo_matrix_t matrix = get_orientation_matrix(
+		self->orientation, surface_width_px, surface_height_px);
+	cairo_pattern_set_matrix(cairo_get_source(cr), &matrix);
+	cairo_paint(cr);
+}
+
+static gboolean
+print(FastivView *self)
+{
+	GtkPrintOperation *print = gtk_print_operation_new();
+	gtk_print_operation_set_n_pages(print, 1);
+	gtk_print_operation_set_embed_page_setup(print, TRUE);
+	gtk_print_operation_set_unit(print, GTK_UNIT_INCH);
+	gtk_print_operation_set_job_name(print, "Image");
+	g_signal_connect(print, "draw-page", G_CALLBACK(on_draw_page), self);
+
+	static GtkPrintSettings *settings = NULL;
+	if (settings != NULL)
+		gtk_print_operation_set_print_settings(print, settings);
+
+	GError *error = NULL;
+	GtkWindow *window = get_toplevel(GTK_WIDGET(self));
+	GtkPrintOperationResult res = gtk_print_operation_run(
+		print, GTK_PRINT_OPERATION_ACTION_PRINT_DIALOG, window, &error);
+	if (res == GTK_PRINT_OPERATION_RESULT_APPLY) {
+		if (settings != NULL)
+			g_object_unref(settings);
+		settings = g_object_ref(gtk_print_operation_get_print_settings(print));
+	}
+	if (error)
+		show_error_dialog(window, error);
+
+	g_object_unref(print);
+	return TRUE;
+}
+
 static gboolean
 save_as(FastivView *self, gboolean frame)
 {
-	GtkWindow *window = NULL;
-	GtkWidget *widget = NULL;
-	if (GTK_IS_WINDOW((widget = gtk_widget_get_toplevel(GTK_WIDGET(self)))))
-		window = GTK_WINDOW(widget);
+	GtkWindow *window = get_toplevel(GTK_WIDGET(self));
+	GtkWidget *dialog = gtk_file_chooser_dialog_new(
+		frame ? "Save frame as" : "Save page as",
+		window, GTK_FILE_CHOOSER_ACTION_SAVE,
+		"_Cancel", GTK_RESPONSE_CANCEL, "_Save", GTK_RESPONSE_ACCEPT, NULL);
 
-	GtkWidget *dialog =
-		gtk_file_chooser_dialog_new(frame ? "Save frame as" : "Save page as",
-			window, GTK_FILE_CHOOSER_ACTION_SAVE,
-			"_Cancel", GTK_RESPONSE_CANCEL, "_Save", GTK_RESPONSE_ACCEPT, NULL);
 	GtkFileChooser *chooser = GTK_FILE_CHOOSER(dialog);
 
 	// TODO(p): Consider a hard dependency on libwebp, or clean this up.
@@ -651,6 +717,8 @@ fastiv_view_key_press_event(GtkWidget *widget, GdkEventKey *event)
 			return set_scale(self, self->scale * SCALE_STEP);
 		case GDK_KEY_minus:
 			return set_scale(self, self->scale / SCALE_STEP);
+		case GDK_KEY_p:
+			return print(self);
 		case GDK_KEY_s:
 			return save_as(self, FALSE);
 		case GDK_KEY_S:

meson.build

@@ -21,7 +21,6 @@ libwebp = dependency('libwebp', required : get_option('libwebp'))
 libwebpdemux = dependency('libwebpdemux', required : get_option('libwebp'))
 libwebpdecoder = dependency('libwebpdecoder', required : get_option('libwebp'))
 libwebpmux = dependency('libwebpmux', required : get_option('libwebp'))
-libwebpencoder = dependency('libwebpencoder', required : get_option('libwebp'))
 libheif = dependency('libheif', required : get_option('libheif'))
 libtiff = dependency('libtiff-4', required : get_option('libtiff'))
 gdkpixbuf = dependency('gdk-pixbuf-2.0', required : get_option('gdk-pixbuf'))
@@ -38,7 +37,6 @@ dependencies = [
 	libwebpdemux,
 	libwebpdecoder,
 	libwebpmux,
-	libwebpencoder,
 	libheif,
 	libtiff,
 	gdkpixbuf,