wrlib: Improvement in the alpha channel support.

There are some problems in the alpha channel support, as is
reported at http://bugs.debian.org/cgi-bin/bugreport.cgi?bug=72917

This patch add a new RCombineAlpha function, based on Gimp. This
function is called when needed in the raster.c functions.

This patch is based on the Brad Jorsch <anomie@users.sourceforge.net>
patch for the 0.62.1-0.1 version.

[crmafra: v1 was sent by Rodolfo kix Garcia <kix@kix.es>]

wrlib/Makefile.am

@@ -20,6 +20,7 @@ include_HEADERS = wraster.h
 
 libwraster_la_SOURCES = 	\
 	raster.c 	\
+	alpha_combine.c \
 	draw.c		\
 	color.c		\
 	load.c 		\

wrlib/alpha_combine.c

@@ -0,0 +1,66 @@
+/* alpha_combine.c - Alpha channel combination, based on Gimp 1.1.24
+ * The GIMP -- an image manipulation program
+ * Copyright (C) 1995 Spencer Kimball and Peter Mattis
+ *
+ *  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., 675 Mass Ave, Cambridge, MA 02139, USA.
+ */
+
+#include "wraster.h"
+
+void RCombineAlpha(unsigned char *d, unsigned char *s, int s_has_alpha,
+		   int width, int height, int dwi, int swi, int opacity) {
+	int x, y;
+	int t, sa;
+	int alpha;
+	float ratio, cratio;
+
+	for (y=0; y<height; y++) {
+		for (x=0; x<width; x++) {
+			sa=s_has_alpha?*(s+3):255;
+
+			if (opacity!=255) {
+				t = sa * opacity + 0x80;
+				sa = ((t>>8)+t)>>8;
+			}
+
+			t = *(d+3) * (255-sa) + 0x80;
+			alpha = sa + (((t>>8)+t)>>8);
+
+			if (sa==0 || alpha==0) {
+				ratio = 0;
+				cratio = 1.0;
+			} else if(sa == alpha) {
+				ratio = 1.0;
+				cratio = 0;
+			} else {
+				ratio = (float)sa / alpha;
+				cratio = 1.0 - ratio;
+			}
+
+			*d = (int)*d * cratio + (int)*s * ratio;
+			s++; d++;
+			*d = (int)*d * cratio + (int)*s * ratio;
+			s++; d++;
+			*d = (int)*d * cratio + (int)*s * ratio;
+			s++; d++;
+			*d = alpha;
+			d++;
+
+			if (s_has_alpha) s++;
+		}
+		d+=dwi;
+		s+=swi;
+	}
+}

wrlib/draw.c

@@ -143,6 +143,7 @@ static void operatePixel(RImage * image, int ofs, int operation, RColor * color)
 			*sr = (((int)*sr * nalpha) + ((int)color->red * alpha)) / 256;
 			*sg = (((int)*sg * nalpha) + ((int)color->green * alpha)) / 256;
 			*sb = (((int)*sb * nalpha) + ((int)color->blue * alpha)) / 256;
+			*sa = alpha + ((int)*sa * nalpha) / 256;
 		}
 		break;
 	case RAddOperation:

wrlib/raster.c

@@ -171,7 +171,7 @@ void RCombineImages(RImage * image, RImage * src)
 					*d++ = *s++;
 					*d++ = *s++;
 					*d++ = *s++;
-					d++;
+					*d++ = 255;
 				}
 			}
 		}
@@ -200,20 +200,7 @@ void RCombineImages(RImage * image, RImage * src)
 				s++;
 			}
 		} else {
-			for (i = 0; i < image->height * image->width; i++) {
+			RCombineAlpha(d, s, 1, image->width, image->height, 0, 0, 255);
-				alpha = *(s + 3);
-				calpha = 255 - alpha;
-				*d = (((int)*d * calpha) + ((int)*s * alpha)) / 256;
-				d++;
-				s++;
-				*d = (((int)*d * calpha) + ((int)*s * alpha)) / 256;
-				d++;
-				s++;
-				*d = (((int)*d * calpha) + ((int)*s * alpha)) / 256;
-				d++;
-				s++;
-				*d++ |= *s++;
-			}
 		}
 	}
 }
@@ -237,7 +224,7 @@ void RCombineImagesWithOpaqueness(RImage * image, RImage * src, int opaqueness)
 #define COP c_opaqueness
 
 	if (!HAS_ALPHA(src)) {
-		int dalpha = HAS_ALPHA(image);
+		if (!HAS_ALPHA(image)) {
 			for (i = 0; i < image->width * image->height; i++) {
 				*d = (((int)*d * (int)COP) + ((int)*s * (int)OP)) / 256;
 				d++;
@@ -248,9 +235,9 @@ void RCombineImagesWithOpaqueness(RImage * image, RImage * src, int opaqueness)
 				*d = (((int)*d * (int)COP) + ((int)*s * (int)OP)) / 256;
 				d++;
 				s++;
-			if (dalpha) {
-				d++;
 			}
+		} else {
+			RCombineAlpha(d, s, 0, image->width, image->height, 0, 0, OP);
 		}
 	} else {
 		int tmp;
@@ -270,21 +257,7 @@ void RCombineImagesWithOpaqueness(RImage * image, RImage * src, int opaqueness)
 				s++;
 			}
 		} else {
-			for (i = 0; i < image->width * image->height; i++) {
+			RCombineAlpha(d, s, 1, image->width, image->height, 0, 0, opaqueness);
-				tmp = (*(s + 3) * opaqueness) / 256;
-				*d = (((int)*d * (255 - tmp)) + ((int)*s * tmp)) / 256;
-				d++;
-				s++;
-				*d = (((int)*d * (255 - tmp)) + ((int)*s * tmp)) / 256;
-				d++;
-				s++;
-				*d = (((int)*d * (255 - tmp)) + ((int)*s * tmp)) / 256;
-				d++;
-				s++;
-				*d |= tmp;
-				d++;
-				s++;
-			}
 		}
 	}
 #undef OP
@@ -360,7 +333,7 @@ void RCombineArea(RImage * image, RImage * src, int sx, int sy, unsigned width,
 					*d++ = *s++;
 					*d++ = *s++;
 					*d++ = *s++;
-					d++;
+					*d++ = 255;
 				}
 				d += dwi;
 				s += swi;
@@ -379,6 +352,7 @@ void RCombineArea(RImage * image, RImage * src, int sx, int sy, unsigned width,
 			d = image->data + (dy * (int)image->width + dx) * 3;
 		}
 
+		if (!dalpha) {
 			for (y = 0; y < height; y++) {
 				for (x = 0; x < width; x++) {
 					alpha = *(s + 3);
@@ -393,12 +367,13 @@ void RCombineArea(RImage * image, RImage * src, int sx, int sy, unsigned width,
 					s++;
 					d++;
 					s++;
-				if (dalpha)
-					d++;
 				}
 				d += dwi;
 				s += swi;
 			}
+		} else {
+			RCombineAlpha(d, s, 1, width, height, dwi, swi, 255);
+		}
 	}
 }
 
@@ -502,6 +477,7 @@ RCombineAreaWithOpaqueness(RImage * image, RImage * src, int sx, int sy,
 		s = src->data + (sy * src->width + sx) * 3;
 		swi = (src->width - width) * 3;
 
+		if (!dalpha) {
 			for (y = 0; y < height; y++) {
 				for (x = 0; x < width; x++) {
 					*d = (((int)*d * (int)COP) + ((int)*s * (int)OP)) / 256;
@@ -513,18 +489,20 @@ RCombineAreaWithOpaqueness(RImage * image, RImage * src, int sx, int sy,
 					*d = (((int)*d * (int)COP) + ((int)*s * (int)OP)) / 256;
 					s++;
 					d++;
-				if (dalpha)
-					d++;
 				}
 				d += dwi;
 				s += swi;
 			}
+		} else {
+			RCombineAlpha(d, s, 0, width, height, dwi, swi, OP);
+		}
 	} else {
 		int tmp;
 
 		s = src->data + (sy * src->width + sx) * 4;
 		swi = (src->width - width) * 4;
 
+		if (!dalpha) {
 			for (y = 0; y < height; y++) {
 				for (x = 0; x < width; x++) {
 					tmp = (*(s + 3) * opaqueness) / 256;
@@ -538,12 +516,13 @@ RCombineAreaWithOpaqueness(RImage * image, RImage * src, int sx, int sy,
 					d++;
 					s++;
 					s++;
-				if (dalpha)
-					d++;
 				}
 				d += dwi;
 				s += swi;
 			}
+		} else {
+			RCombineAlpha(d, s, 1, width, height, dwi, swi, OP);
+		}
 	}
 #undef OP
 #undef COP
@@ -627,12 +606,12 @@ RImage *RMakeCenteredImage(RImage * image, unsigned width, unsigned height, RCol
 	int x, y, w, h, sx, sy;
 	RImage *tmp;
 
-	tmp = RCreateImage(width, height, False);
+	tmp = RCreateImage(width, height, HAS_ALPHA(image));
 	if (!tmp) {
 		return NULL;
 	}
 
-	RClearImage(tmp, color);
+	RFillImage(tmp, color);
 
 	if (image->height < height) {
 		h = image->height;

wrlib/wraster.h

@@ -356,6 +356,9 @@ void RCombineAreaWithOpaqueness(RImage *image, RImage *src, int sx, int sy,
                                 unsigned width, unsigned height, int dx, int dy,
                                 int opaqueness);
 
+void RCombineAlpha(unsigned char *d, unsigned char *s, int s_has_alpha,
+		   int width, int height, int dwi, int swi, int opacity);
+
 RImage *RScaleImage(RImage *image, unsigned new_width, unsigned new_height);
 
 RImage *RSmoothScaleImage(RImage *src, unsigned new_width,