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Re: Alpha compositing in gnustep-back
|
From: |
Jeff Teunissen |
|
Subject: |
Re: Alpha compositing in gnustep-back |
|
Date: |
Fri, 12 Jul 2002 04:51:21 -0400 |
Whoops! Sent the wrong patch. Here's a better one.
--
| Jeff Teunissen -=- Pres., Dusk To Dawn Computing -=- deek @ d2dc.net
| GPG: 1024D/9840105A 7102 808A 7733 C2F3 097B 161B 9222 DAB8 9840 105A
| Core developer, The QuakeForge Project http://www.quakeforge.net/
| Specializing in Debian GNU/Linux http://www.d2dc.net/~deek/
Index: back/Source/xlib/XGBitmap.m
===================================================================
RCS file: /cvsroot/gnustep/gnustep/core/back/Source/xlib/XGBitmap.m,v
retrieving revision 1.2
diff -u -w -r1.2 XGBitmap.m
--- back/Source/xlib/XGBitmap.m 10 May 2002 15:06:17 -0000 1.2
+++ back/Source/xlib/XGBitmap.m 12 Jul 2002 08:29:40 -0000
@@ -54,26 +54,26 @@
#define InitRGBShiftsAndMasks(rs,rw,gs,gw,bs,bw,as,aw) \
do { \
- _rshift = rs; \
- _rmask = (1<<rw) -1; \
- _rwidth = rw; \
- _gshift = gs; \
- _gmask = (1<<gw) -1; \
- _gwidth = gw; \
- _bshift = bs; \
- _bmask = (1<<bw) -1; \
- _bwidth = bw; \
- _amask = (1<<aw) -1; \
- _ashift = as; \
- _awidth = aw; \
+ _rshift = (rs); \
+ _rmask = (1<<(rw)) -1; \
+ _rwidth = (rw); \
+ _gshift = (gs); \
+ _gmask = (1<<(gw)) -1; \
+ _gwidth = (gw); \
+ _bshift = (bs); \
+ _bmask = (1<<(bw)) -1; \
+ _bwidth = (bw); \
+ _amask = (1<<(aw)) -1; \
+ _ashift = (as); \
+ _awidth = (aw); \
} while(0)
#define PixelToRGB(pixel,r,g,b) \
do { \
- r = (pixel >> _rshift) & _rmask; \
- g = (pixel >> _gshift) & _gmask; \
- b = (pixel >> _bshift) & _bmask; \
+ (r) = (pixel >> _rshift) & _rmask; \
+ (g) = (pixel >> _gshift) & _gmask; \
+ (b) = (pixel >> _bshift) & _bmask; \
} while(0)
/* Note that RGBToPixel assumes that the
@@ -88,6 +88,10 @@
|((b) << _bshift); \
} while(0)
+#define CLAMP(a) \
+ do { \
+ (a) = MAX(0, MIN(255, (a))); \
+ } while (0)
/* Composite source image (pixmap) onto a destination image with alpha.
Only works for op=Sover now
@@ -107,14 +111,9 @@
float fraction)
{
unsigned long pixel;
- unsigned short oldAlpha = 0;
unsigned long oldPixel = 0;
- unsigned short oldAr = 0;
- unsigned short oldAg = 0;
- unsigned short oldAb = 0;
- unsigned char oldBr = 0;
- unsigned char oldBg = 0;
- unsigned char oldBb = 0;
+
+ fraction = MAX(0.0, MIN(1.0, fraction));
if (drawMechanism == XGDM_FAST15
|| drawMechanism == XGDM_FAST16
@@ -144,68 +143,70 @@
//which picture goes wrong.
InitRGBShiftsAndMasks(11,5,5,6,0,5,0,8);
}
+
for (row = 0; row < srect.height; row++)
{
unsigned col;
for (col = 0; col < srect.width; col++)
{
- unsigned r, g, b, alpha;
- pixel = XGetPixel(source_im->image,
- col+srect.x, row+srect.y);
-
- PixelToRGB(pixel,r,g,b);
+ unsigned sr, sg, sb, sa; // source
+ unsigned dr, dg, db, da; // dest
+ double alpha, ialpha;
+
+ // Get the source pixel information
+ pixel = XGetPixel (source_im->image, srect.x+col, srect.y+row);
+ PixelToRGB (pixel, sr, sg, sb);
- pixel = 255;
if (source_alpha)
+ {
pixel = XGetPixel(source_alpha->image,
- col+srect.x, row+srect.y);
+ srect.x+col, srect.y+row);
+ sa = (pixel >> _ashift) & _amask;
+ }
+ else
+ sa = _amask;
- if (fraction < 1)
- pixel *= fraction;
- alpha = (pixel >> _ashift) & _amask;
+ if (sa == 0) // dest wouldn't be changed
+ continue;
- if (alpha == 0)
- continue; // background unchanged.
- if (alpha != _amask)
- { // We really have something to mix!
- unsigned short ialpha = _amask - alpha;
- /*
- * Get the background pixel and convert to RGB.
- */
+ if (fraction < 1.0)
+ sa *= fraction;
+
+ alpha = ((double) sa) / _amask;
+
+ // Now get dest pixel
pixel = XGetPixel(dest_im->image, col, row);
- if (pixel != oldPixel)
+ PixelToRGB (pixel, dr, dg, db);
+
+ if (dest_alpha)
{
- oldPixel = pixel;
- PixelToRGB(pixel, oldBr,oldBg,oldBb);
- oldAlpha = 0;
- }
- if (alpha != oldAlpha)
- {
- oldAlpha = alpha;
- oldAr = ialpha * oldBr;
- oldAg = ialpha * oldBg;
- oldAb = ialpha * oldBb;
+ pixel = XGetPixel(dest_alpha->image, col, row);
+ da = (pixel >> _ashift) & _amask;
}
+ else // no alpha channel, background is opaque
+ da = _amask;
- // mix in alpha to produce RGB out
- r = (oldAr + (r*alpha))/_amask;
- g = (oldAg + (g*alpha))/_amask;
- b = (oldAb + (b*alpha))/_amask;
- }
- RGBToPixel(r,g,b,pixel);
+ ialpha = (1.0 - alpha);
+ dr = (sr * alpha) + (dr * ialpha);
+ dg = (sg * alpha) + (dg * ialpha);
+ db = (sb * alpha) + (db * ialpha);
+
+ // calc final alpha
+ if (sa == _amask || da == _amask)
+ da = _amask;
+ else
+ da = sa + (da * ialpha);
+
+ CLAMP(dr);
+ CLAMP(dg);
+ CLAMP(db);
+ CLAMP(da);
+
+ RGBToPixel(dr, dg, db, pixel);
XPutPixel(dest_im->image, col, row, pixel);
if (dest_alpha)
- {
- unsigned short dalpha;
- unsigned long dpixel;
- /* Alpha gets mixed the same as all the
- other color components */
- dpixel = XGetPixel(dest_alpha->image, col, row);
- dalpha = (dpixel >> _ashift) & _amask;
- dalpha = alpha + dalpha * (_amask - alpha)/_amask;
- XPutPixel(dest_alpha->image, col, row, dalpha << _ashift );
- }
+ XPutPixel(dest_alpha->image, col, row, da << _ashift);
}
}
}
@@ -222,7 +223,6 @@
pixel = (unsigned long)-1; // Never valid?
c2.pixel = pixel;
-
for (row = 0; row < srect.height; row++)
{
unsigned col;
@@ -858,14 +858,6 @@
{
unsigned long pixel;
- unsigned short oldAlpha = 0;
- unsigned long oldPixel = 0;
- unsigned short oldAr = 0;
- unsigned short oldAg = 0;
- unsigned short oldAb = 0;
- unsigned char oldBr = 0;
- unsigned char oldBg = 0;
- unsigned char oldBb = 0;
/* Two cases, the *_FAST* method, which
is covered in the first a part of the if
@@ -915,74 +907,69 @@
for (col = 0; col < drect.width; col++)
{
- unsigned short r = *rptr++;
- unsigned short g = *gptr++;
- unsigned short b = *bptr++;
- unsigned short alpha = *aptr++;;
+ unsigned short sr = (*rptr++ >> (8 - _rwidth));
+ unsigned short sg = (*gptr++ >> (8 - _gwidth));
+ unsigned short sb = (*bptr++ >> (8 - _bwidth));
+ unsigned short sa = (*aptr++ >> (8 - _awidth));
+ unsigned dr, dg, db, da;
+ double alpha = (double) sa / ((1 << _rwidth) - 1);
+
+ if (sa == 0) // dest wouldn't be changed
+ continue;
/*
- * Convert 8-bit components down to the 5-bit values
- * that the display system can actually handle.
+ * I don't know why, but colors are scaled by alpha. This
+ * shouldn't be happening, but it is!
*/
- r >>= (8 - _rwidth);
- g >>= (8 - _gwidth);
- b >>= (8 - _bwidth);
-
- if (has_alpha)
+ if (sa < _amask)
{
- if (dest_alpha)
- {
- unsigned short dalpha;
- unsigned long dpixel;
- /* Alpha gets mixed the same as all the
- other color components */
- dpixel = XGetPixel(dest_alpha->image, col, row);
- dalpha = (dpixel >> _ashift) & _amask;
- dalpha = alpha + dalpha * (_amask - alpha)/_amask;
- XPutPixel(dest_alpha->image, col, row,
- dalpha << _ashift);
+ double multiplier = (double) _amask / sa;
+
+ sr *= multiplier;
+ sg *= multiplier;
+ sb *= multiplier;
}
- if (alpha == 0)
- continue; // background unchanged.
- if (alpha != _amask)
- {
- unsigned short ialpha = _amask - alpha;
- /*
- * Get the background pixel and convert to RGB.
- */
+ // get the destination pixel
pixel = XGetPixel(dest_im->image, col, row);
- if (pixel != oldPixel)
+ PixelToRGB(pixel, dr, dg, db);
+
+ if (dest_alpha)
{
- oldPixel = pixel;
- PixelToRGB(pixel,oldBr,oldBg,oldBb);
- oldAlpha = 0;
- }
- if (alpha != oldAlpha)
- {
- oldAlpha = alpha;
- oldAr = ialpha * oldBr;
- oldAg = ialpha * oldBg;
- oldAb = ialpha * oldBb;
+ pixel = XGetPixel(dest_alpha->image, col, row);
+ da = (pixel >> _ashift) & _amask;
}
+ else // no alpha channel, background is opaque
+ da = _amask;
- // mix in alpha to produce RGB out
- r = (oldAr + (r * alpha)) / _amask;
- g = (oldAg + (g * alpha)) / _amask;
- b = (oldAb + (b * alpha)) / _amask;
- }
+ if (sa == _amask || da == 0) // source only
+ {
+ dr = sr;
+ dg = sg;
+ db = sb;
+ da = sa;
}
else
{
- /* Not using alpha, but we still have to set it
- in the pixmap */
- if (dest_alpha)
- XPutPixel(dest_alpha->image, col, row,
- _amask << _ashift);
+ double ialpha = (1.0 - alpha);
+ dr = (sr * alpha) + (dr * ialpha);
+ dg = (sg * alpha) + (dg * ialpha);
+ db = (sb * alpha) + (db * ialpha);
+ if (da == _amask || da == _amask)
+ da = _amask;
+ else
+ da = sa + (da * ialpha);
}
- RGBToPixel(r,g,b,pixel);
+ CLAMP(dr);
+ CLAMP(dg);
+ CLAMP(db);
+ CLAMP(da);
+
+ RGBToPixel(dr, dg, db, pixel);
XPutPixel(dest_im->image, col, row, pixel);
+ if (dest_alpha)
+ XPutPixel(dest_alpha->image, col, row, da << _ashift);
}
}
}