Move thumbnails into their own source file

And clean up identifiers.

fiv-thumbnail.h

@@ -0,0 +1,64 @@
+//
+// fiv-thumbnail.h: thumbnail management
+//
+// Copyright (c) 2021, Přemysl Eric Janouch <p@janouch.name>
+//
+// Permission to use, copy, modify, and/or distribute this software for any
+// purpose with or without fee is hereby granted.
+//
+// THE SOFTWARE IS PROVIDED "AS IS" AND THE AUTHOR DISCLAIMS ALL WARRANTIES
+// WITH REGARD TO THIS SOFTWARE INCLUDING ALL IMPLIED WARRANTIES OF
+// MERCHANTABILITY AND FITNESS. IN NO EVENT SHALL THE AUTHOR BE LIABLE FOR ANY
+// SPECIAL, DIRECT, INDIRECT, OR CONSEQUENTIAL DAMAGES OR ANY DAMAGES
+// WHATSOEVER RESULTING FROM LOSS OF USE, DATA OR PROFITS, WHETHER IN AN ACTION
+// OF CONTRACT, NEGLIGENCE OR OTHER TORTIOUS ACTION, ARISING OUT OF OR IN
+// CONNECTION WITH THE USE OR PERFORMANCE OF THIS SOFTWARE.
+//
+
+#pragma once
+
+#include <cairo.h>
+#include <gio/gio.h>
+#include <glib.h>
+
+// And this is how you avoid glib-mkenums.
+typedef enum _FivThumbnailSize {
+#define FIV_THUMBNAIL_SIZES(XX) \
+	XX(SMALL,  128, "normal") \
+	XX(NORMAL, 256, "large") \
+	XX(LARGE,  512, "x-large") \
+	XX(HUGE,  1024, "xx-large")
+#define XX(name, value, dir) FIV_THUMBNAIL_SIZE_ ## name,
+	FIV_THUMBNAIL_SIZES(XX)
+#undef XX
+	FIV_THUMBNAIL_SIZE_COUNT,
+
+	FIV_THUMBNAIL_SIZE_MIN = 0,
+	FIV_THUMBNAIL_SIZE_MAX = FIV_THUMBNAIL_SIZE_COUNT - 1
+} FivThumbnailSize;
+
+GType fiv_thumbnail_size_get_type(void) G_GNUC_CONST;
+#define FIV_TYPE_THUMBNAIL_SIZE (fiv_thumbnail_size_get_type())
+
+typedef struct _FivThumbnailSizeInfo {
+	int size;                           ///< Nominal size in pixels
+	const char *thumbnail_spec_name;    ///< thumbnail-spec directory name
+} FivThumbnailSizeInfo;
+
+extern FivThumbnailSizeInfo fiv_thumbnail_sizes[FIV_THUMBNAIL_SIZE_COUNT];
+
+enum { FIV_THUMBNAIL_WIDE_COEFFICIENT = 2 };
+
+/// If non-NULL, indicates a thumbnail of insufficient quality.
+extern cairo_user_data_key_t fiv_thumbnail_key_lq;
+
+/// Returns this user's root thumbnail directory.
+gchar *fiv_thumbnail_get_root(void);
+
+/// Generates wide thumbnails of up to the specified size, saves them in cache.
+gboolean fiv_thumbnail_produce(
+	GFile *target, FivThumbnailSize max_size, GError **error);
+
+/// Retrieves a thumbnail of the most appropriate quality and resolution
+/// for the target file.
+cairo_surface_t *fiv_thumbnail_lookup(GFile *target, FivThumbnailSize size);