[gthumb] image viewer: added ability to define the transparency style

[Paolo Bacchilega <paobac src gnome org>]

commit e0399e29502f6b3c4d9673340653e7c51fe11796
Author: Paolo Bacchilega <paobac src gnome org>
Date:   Mon Nov 4 11:09:12 2019 +0100

    image viewer: added ability to define the transparency style

 gthumb/gth-image-viewer.c | 43 +++++++++++++++++++++++++++++++++++++++----
 gthumb/gth-image-viewer.h | 12 ++++++++++++
 2 files changed, 51 insertions(+), 4 deletions(-)
---
diff --git a/gthumb/gth-image-viewer.c b/gthumb/gth-image-viewer.c
index fc0e022a..a6224841 100644
--- a/gthumb/gth-image-viewer.c
+++ b/gthumb/gth-image-viewer.c
@@ -40,7 +40,7 @@
 #define MINIMUM_DELAY   10    /* When an animation frame has a 0 milli seconds
                               * delay use this delay instead. */
 #define STEP_INCREMENT  20.0  /* Scroll increment. */
-#define BLACK_VALUE 0.2
+#define GRAY_VALUE 0.2
 #define CHECKED_PATTERN_SIZE 20
 
 
@@ -113,7 +113,7 @@ struct _GthImageViewerPrivate {
        gboolean                skip_zoom_change;
        gboolean                update_image_after_zoom;
        gboolean                reset_scrollbars;
-
+       GthTransparencyStyle    transparency_style;
        GList                  *painters;
 };
 
@@ -1576,6 +1576,7 @@ gth_image_viewer_init (GthImageViewer *self)
        self->priv->cursor_void = NULL;
 
        self->priv->reset_scrollbars = TRUE;
+       self->priv->transparency_style = GTH_TRANSPARENCY_STYLE_CHECKERED;
 
        gth_image_viewer_set_tool (self, NULL);
 
@@ -2283,6 +2284,26 @@ gth_image_viewer_get_tool (GthImageViewer *self)
 }
 
 
+void
+gth_image_viewer_set_transparency_style (GthImageViewer       *self,
+                                        GthTransparencyStyle  style)
+{
+       g_return_if_fail (GTH_IS_IMAGE_VIEWER (self));
+
+       self->priv->transparency_style = style;
+       gtk_widget_queue_draw (GTK_WIDGET (self));
+}
+
+
+GthTransparencyStyle
+gth_image_viewer_get_transparency_style (GthImageViewer *self)
+{
+       g_return_val_if_fail (GTH_IS_IMAGE_VIEWER (self), 0);
+
+       return self->priv->transparency_style;
+}
+
+
 void
 gth_image_viewer_scroll_to (GthImageViewer *self,
                            int             x_offset,
@@ -2645,7 +2666,7 @@ gth_image_viewer_paint_background (GthImageViewer *self,
 
        cairo_save (cr);
        gtk_widget_get_allocation (GTK_WIDGET (self), &allocation);
-       cairo_set_source_rgb (cr, BLACK_VALUE, BLACK_VALUE, BLACK_VALUE);
+       cairo_set_source_rgb (cr, GRAY_VALUE, GRAY_VALUE, GRAY_VALUE);
        cairo_rectangle (cr,
                         0,
                         0,
@@ -2685,7 +2706,21 @@ gth_image_viewer_paint_frame (GthImageViewer *self,
 
        /* background */
 
-       cairo_set_source (cr, self->priv->background_pattern);
+       switch (self->priv->transparency_style) {
+       case GTH_TRANSPARENCY_STYLE_CHECKERED:
+               cairo_set_source (cr, self->priv->background_pattern);
+               break;
+       case GTH_TRANSPARENCY_STYLE_WHITE:
+               cairo_set_source_rgb (cr, 1.0, 1.0, 1.0);
+               break;
+       case GTH_TRANSPARENCY_STYLE_GRAY:
+               cairo_set_source_rgb (cr, GRAY_VALUE, GRAY_VALUE, GRAY_VALUE);
+               break;
+       case GTH_TRANSPARENCY_STYLE_BLACK:
+               cairo_set_source_rgb (cr, 0.0, 0.0, 0.0);
+               break;
+       }
+
        cairo_rectangle (cr,
                         self->image_area.x,
                         self->image_area.y,
diff --git a/gthumb/gth-image-viewer.h b/gthumb/gth-image-viewer.h
index 9754b7fe..f04abcfc 100644
--- a/gthumb/gth-image-viewer.h
+++ b/gthumb/gth-image-viewer.h
@@ -77,6 +77,14 @@ typedef enum {
 } GthZoomChange;
 
 
+typedef enum {
+       GTH_TRANSPARENCY_STYLE_CHECKERED,
+       GTH_TRANSPARENCY_STYLE_WHITE,
+       GTH_TRANSPARENCY_STYLE_GRAY,
+       GTH_TRANSPARENCY_STYLE_BLACK
+} GthTransparencyStyle;
+
+
 struct _GthImageViewer
 {
        GtkWidget __parent;
@@ -224,6 +232,10 @@ void           gth_image_viewer_set_tool                 (GthImageViewer
                                                          GthImageViewerTool    *tool);
 GthImageViewerTool *
               gth_image_viewer_get_tool                 (GthImageViewer        *viewer);
+void           gth_image_viewer_set_transparency_style   (GthImageViewer        *viewer,
+                                                         GthTransparencyStyle   style);
+GthTransparencyStyle
+              gth_image_viewer_get_transparency_style   (GthImageViewer        *viewer);
 
 /* Scrolling. */