New function to threshold a pixbuf's alpha channel into a bitmap.

1999-10-27  Federico Mena Quintero  <federico@redhat.com>

	* src/gdk-pixbuf-render.c (gdk_pixbuf_render_threshold_alpha): New
	function to threshold a pixbuf's alpha channel into a bitmap.

	* src/gdk-pixbuf.c (gdk_pixbuf_new): Fixed so that it will
	contemplate future extensions to ArtPixBuf's formats.

	* src/io-png.c (png_info_callback): Use the new API of gdk_pixbuf_new().

	* src/gdk-pixbuf.h (gdk_pixbuf_get_height): Added some convenience
	macros to fetch the ArtPixBuf's fields.

1 files changed, 149 insertions, 0 deletions

diff --git a/gdk/gdkpixbuf-render.c b/gdk/gdkpixbuf-render.c
new file mode 100644
index 000000000..674da391b
--- /dev/null
+++ b/gdk/gdkpixbuf-render.c
@@ -0,0 +1,149 @@
+/* GdkPixbuf library - Rendering functions
+ *
+ * Copyright (C) 1999 The Free Software Foundation
+ *
+ * Author: Federico Mena-Quintero <federico@gimp.org>
+ *
+ * This library is free software; you can redistribute it and/or
+ * modify it under the terms of the GNU Library General Public
+ * License as published by the Free Software Foundation; either
+ * version 2 of the License, or (at your option) any later version.
+ *
+ * This library is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
+ * Library General Public License for more details.
+ *
+ * You should have received a copy of the GNU Library General Public
+ * License along with this library; if not, write to the
+ * Free Software Foundation, Inc., 59 Temple Place - Suite 330,
+ * Boston, MA 02111-1307, USA.
+ */
+
+#include <config.h>
+#include <gdk/gdk.h>
+#include <libart_lgpl/art_rect.h>
+#include "gdk-pixbuf.h"
+
+
+
+/**
+ * gdk_pixbuf_render_threshold_alpha:
+ * @pixbuf: A pixbuf.
+ * @bitmap: Bitmap where the bilevel mask will be painted to.
+ * @src_x: Source X coordinate.
+ * @src_y: source Y coordinate.
+ * @dest_x: Destination X coordinate.
+ * @dest_y: Destination Y coordinate.
+ * @width: Width of region to threshold.
+ * @height: Height of region to threshold.
+ * @alpha_threshold: Opacity values below this will be painted as zero; all
+ * other values will be painted as one.
+ * 
+ * Takes the opacity values in a pixbuf and thresholds them to produce a
+ * bi-level alpha mask that can be used as a clipping mask for a drawable.
+ **/
+void
+gdk_pixbuf_render_threshold_alpha (GdkPixbuf *pixbuf, GdkBitmap *bitmap,
+				   int src_x, int src_y,
+				   int dest_x, int dest_y,
+				   int width, int height,
+				   int alpha_threshold)
+{
+	ArtPixBuf *apb;
+	GdkGC *gc;
+	GdkColor color;
+	int x, y;
+	guchar *p;
+	int start, start_status;
+	int status;
+
+	g_return_if_fail (pixbuf != NULL);
+	apb = pixbuf->art_pixbuf;
+
+	g_return_if_fail (apb->format == ART_PIX_RGB);
+	g_return_if_fail (apb->n_channels == 3 || apb->n_channels == 4);
+	g_return_if_fail (apb->bits_per_sample == 8);
+
+	g_return_if_fail (bitmap != NULL);
+	g_return_if_fail (src_x >= 0 && src_x + width <= apb->width);
+	g_return_if_fail (src_y >= 0 && src_y + height <= apb->height);
+
+	g_return_if_fail (alpha_threshold >= 0 && alpha_threshold <= 255);
+
+	gc = gdk_gc_new (bitmap);
+
+	if (!apb->has_alpha) {
+		color.pixel = (alpha_threshold == 255) ? 0 : 1;
+		gdk_gc_set_foreground (gc, &color);
+		gdk_draw_rectangle (bitmap, gc, TRUE, dest_x, dest_y, width, height);
+		gdk_gc_unref (gc);
+		return;
+	}
+
+	color.pixel = 0;
+	gdk_gc_set_foreground (gc, &color);
+	gdk_draw_rectangle (bitmap, gc, TRUE, dest_x, dest_y, width, height);
+
+	for (y = 0; y < height; y++) {
+		p = (apb->pixels + (y + src_y) * apb->rowstride + src_x * apb->n_channels
+		     + apb->n_channels - 1);
+
+		start = 0;
+		start_status = *p < alpha_threshold;
+
+		for (x = 0; x < width; x++) {
+			status = *p < alpha_threshold;
+
+			if (status != start_status) {
+				color.pixel = start_status ? 0 : 1;
+				gdk_gc_set_foreground (gc, &color);
+				gdk_draw_line (bitmap, gc,
+					       start + dest_x, y + dest_y,
+					       x - 1 + dest_x, y + dest_y);
+
+				start = x;
+				start_status = status;
+			}
+
+			p += apb->n_channels;
+		}
+
+		color.pixel = start_status ? 0 : 1;
+		gdk_gc_set_foreground (gc, &color);
+		gdk_draw_line (bitmap, gc,
+			       start + dest_x, y + dest_y,
+			       x - 1 + dest_x, y + dest_y);
+	}
+
+	gdk_gc_unref (gc);
+}
+
+void
+gdk_pixbuf_render_to_drawable (GdkPixbuf *pixbuf, GdkDrawable *drawable,
+			       int src_x, int src_y,
+			       int dest_x, int dest_y,
+			       int width, int height,
+			       GdkPixbufAlphaMode alpha_mode,
+			       int alpha_threshold,
+			       GdkRgbDither dither,
+			       int x_dither, int y_dither)
+{
+	ArtPixBuf *apb;
+	ArtIRect dest_rect, req_rect, area_rect;
+	GdkBitmap *bitmap;
+
+	g_return_if_fail (pixbuf != NULL);
+	apb = pixbuf->art_pixbuf;
+
+	g_return_if_fail (apb->format == ART_PIX_RGB);
+	g_return_if_fail (apb->n_channels == 3 || apb->n_channels == 4);
+	g_return_if_fail (apb->bits_per_sample == 8);
+
+	g_return_if_fail (drawable != NULL);
+	g_return_if_fail (src_x >= 0 && src_x + width <= apb->width);
+	g_return_if_fail (src_y >= 0 && src_y + height <= apb->height);
+
+
+	bitmap = gdk_pixmap_new (NULL, width, height, 1);
+}