start to add more blend modes

libvips/conversion/composite.c

@@ -61,7 +61,12 @@
 
 /**
  * VipsBlendMode:
+ * VIPS_BLEND_MODE_CLEAR: 
+ * VIPS_BLEND_MODE_SOURCE: 
  * VIPS_BLEND_MODE_OVER: 
+ * VIPS_BLEND_MODE_IN: 
+ * VIPS_BLEND_MODE_OUT: 
+ * VIPS_BLEND_MODE_ATOP: 
  *
  * The various Porter-Duff blend modes. See vips_composite(), for example. 
  */
@@ -72,6 +77,8 @@
  *
  * https://en.wikipedia.org/wiki/Alpha_compositing
  *
+ * https://www.cairographics.org/operators/
+ *
  * Benchmark:
  *
  * vips replicate PNG_transparency_demonstration_1.png x.png 15 15
@@ -127,8 +134,8 @@ G_DEFINE_TYPE( VipsComposite, vips_composite, VIPS_TYPE_CONVERSION );
 /* Cairo naming conventions:
  *
  * aR	alpha of result			
- * aA	alpha of source A
+ * aA	alpha of source A	(the new pixel)
- * aB	alpha of source B
+ * aB	alpha of source B	(the thing we accumulate)
  * xR	colour channel of result	
  * xA	colour channel of source A
  * xB	colour channel of source B
@@ -136,10 +143,30 @@ G_DEFINE_TYPE( VipsComposite, vips_composite, VIPS_TYPE_CONVERSION );
 
 #define ALPHA( MODE, aR, aA, aB ) { \
 	switch( MODE ) { \
+	case VIPS_BLEND_MODE_CLEAR: \
+		aR = 1 - aA; \
+		break; \
+	\
+	case VIPS_BLEND_MODE_SOURCE: \
+		aR = aA; \
+		break; \
+	\
 	case VIPS_BLEND_MODE_OVER: \
 		aR = aA + aB * (1.0 - aA); \
 		break; \
 	\
+	case VIPS_BLEND_MODE_IN: \
+		aR = aA * aB; \
+		break; \
+	\
+	case VIPS_BLEND_MODE_OUT: \
+		aR = aA * (1 - aB); \
+		break; \
+	\
+	case VIPS_BLEND_MODE_ATOP: \
+		aR = aB; \
+		break; \
+	\
 	default: \
 		 aR = 0; \
 		 g_assert_not_reached(); \
@@ -148,10 +175,30 @@ G_DEFINE_TYPE( VipsComposite, vips_composite, VIPS_TYPE_CONVERSION );
 
 #define BLEND_PREMULTIPLIED( MODE, xR, xA, aA, xB, aB ) { \
 	switch( MODE ) { \
+	case VIPS_BLEND_MODE_CLEAR: \
+		xR = 1 - aA; \
+		break; \
+	\
+	case VIPS_BLEND_MODE_SOURCE: \
+		aR = xA; \
+		break; \
+	\
 	case VIPS_BLEND_MODE_OVER: \
 		xR = xA + xB * (1 - aA); \
 		break; \
 	\
+	case VIPS_BLEND_MODE_IN: \
+		xR = xA; \
+		break; \
+	\
+	case VIPS_BLEND_MODE_OUT: \
+		xR = xA; \
+		break; \
+	\
+	case VIPS_BLEND_MODE_ATOP: \
+		xR = xA + xB * (1 - aA); \
+		break; \
+	\
 	default: \
 		 xR = 0; \
 		 g_assert_not_reached(); \
@@ -160,10 +207,30 @@ G_DEFINE_TYPE( VipsComposite, vips_composite, VIPS_TYPE_CONVERSION );
 
 #define BLEND_MULTIPLY( MODE, xR, aR, xA, aA, xB, aB ) { \
 	switch( MODE ) { \
+	case VIPS_BLEND_MODE_CLEAR: \
+		xR = 1 - aA; \
+		break; \
+	\
+	case VIPS_BLEND_MODE_SOURCE: \
+		aR = xA; \
+		break; \
+	\
 	case VIPS_BLEND_MODE_OVER: \
 		xR = (aA * xA + aB * xB * (1 - aA)) / aR; \
 		break; \
 	\
+	case VIPS_BLEND_MODE_IN: \
+		xR = xA; \
+		break; \
+	\
+	case VIPS_BLEND_MODE_OUT: \
+		xR = xA; \
+		break; \
+	\
+	case VIPS_BLEND_MODE_ATOP: \
+		xR = aA * xA + xB * (1 - aA); \
+		break; \
+	\
 	default: \
 		 xR = 0; \
 		 g_assert_not_reached(); \

libvips/include/vips/conversion.h

@@ -90,7 +90,12 @@ typedef enum {
 } VipsInteresting;
 
 typedef enum {
+	VIPS_BLEND_MODE_CLEAR,
+	VIPS_BLEND_MODE_SOURCE,
 	VIPS_BLEND_MODE_OVER,
+	VIPS_BLEND_MODE_IN,
+	VIPS_BLEND_MODE_OUT,
+	VIPS_BLEND_MODE_ATOP,
 	VIPS_BLEND_MODE_LAST
 } VipsBlendMode;
 

libvips/iofuncs/enumtypes.c

@@ -355,7 +355,12 @@ vips_blend_mode_get_type( void )
 
 	if( etype == 0 ) {
 		static const GEnumValue values[] = {
+			{VIPS_BLEND_MODE_CLEAR, "VIPS_BLEND_MODE_CLEAR", "clear"},
+			{VIPS_BLEND_MODE_SOURCE, "VIPS_BLEND_MODE_SOURCE", "source"},
 			{VIPS_BLEND_MODE_OVER, "VIPS_BLEND_MODE_OVER", "over"},
+			{VIPS_BLEND_MODE_IN, "VIPS_BLEND_MODE_IN", "in"},
+			{VIPS_BLEND_MODE_OUT, "VIPS_BLEND_MODE_OUT", "out"},
+			{VIPS_BLEND_MODE_ATOP, "VIPS_BLEND_MODE_ATOP", "atop"},
 			{VIPS_BLEND_MODE_LAST, "VIPS_BLEND_MODE_LAST", "last"},
 			{0, NULL, NULL}
 		};