From 70a1dc09262be4dbe4ef4e6df45b0c2ed1dafce8 Mon Sep 17 00:00:00 2001
From: John Cupitt <jcupitt@gmail.com>
Date: Tue, 9 Jun 2020 02:04:55 +0100
Subject: [PATCH] Revert "improve transparency support"

This reverts commit 20c9a7f7cc24965df486331738d181f641c075af.
---
 libvips/foreign/spngload.c | 39 ++++++++++++++++++++------------------
 1 file changed, 21 insertions(+), 18 deletions(-)

diff --git a/libvips/foreign/spngload.c b/libvips/foreign/spngload.c
index 8b43aac9..319eafb2 100644
--- a/libvips/foreign/spngload.c
+++ b/libvips/foreign/spngload.c
@@ -41,11 +41,12 @@
  * set a chunk size limit with spng_set_chunks_limits() when that API is done
  *
  * load only, there's no save support for now
+ *
  */
 
 /*
- */
 #define DEBUG
+ */
 
 #ifdef HAVE_CONFIG_H
 #include <config.h>
@@ -315,28 +316,37 @@ vips_foreign_load_png_header( VipsForeignLoad *load )
 
 
 	switch( png->ihdr.color_type ) {
-	case SPNG_COLOR_TYPE_GRAYSCALE_ALPHA:
 	case SPNG_COLOR_TYPE_GRAYSCALE:
 		png->bands = 1;
-		if( !spng_get_trns( png->ctx ) ) 
-			png->bands += 1;
+		png->interpretation = VIPS_INTERPRETATION_B_W;
+		png->fmt = SPNG_FMT_PNG;
+		break;
+
+	case SPNG_COLOR_TYPE_GRAYSCALE_ALPHA:
+		png->bands = 2;
 		png->interpretation = VIPS_INTERPRETATION_B_W;
 		png->fmt = SPNG_FMT_PNG;
 		break;
 
 	case SPNG_COLOR_TYPE_TRUECOLOR:
-	case SPNG_COLOR_TYPE_TRUECOLOR_ALPHA:
 		png->bands = 3;
-		if( !spng_get_trns( png->ctx ) ) 
-			png->bands += 1;
 		png->interpretation = VIPS_INTERPRETATION_sRGB;
 		png->fmt = SPNG_FMT_PNG;
 		break;
 
 	case SPNG_COLOR_TYPE_INDEXED:
+		png->bands = 3;
+		png->interpretation = VIPS_INTERPRETATION_sRGB;
+
+		/* Expand indexed images to RGB8.
+		 */
+		png->fmt = SPNG_FMT_RGB8;
+		break;
+
+	case SPNG_COLOR_TYPE_TRUECOLOR_ALPHA:
 		png->bands = 4;
 		png->interpretation = VIPS_INTERPRETATION_sRGB;
-		png->fmt = SPNG_FMT_RGBA8;
+		png->fmt = SPNG_FMT_PNG;
 		break;
 
 	default:
@@ -447,15 +457,10 @@ vips_foreign_load_png_load( VipsForeignLoad *load )
 		vips_object_local_array( VIPS_OBJECT( load ), 3 );
 
 	int error;
-	enum spng_decode_flags;
 
 	if( vips_source_decode( png->source ) )
 		return( -1 );
 
-	/* We want the alpha, if present.
-	 */
-	flags = SPNG_DECODE_TRNS;
-
 	if( png->ihdr.interlace_method != SPNG_INTERLACE_NONE ) {
 		/* Arg awful interlaced image. We have to load to a huge mem 
 		 * buffer, then copy to out.
@@ -468,7 +473,7 @@ vips_foreign_load_png_load( VipsForeignLoad *load )
 		if( (error = spng_decode_image( png->ctx, 
 			VIPS_IMAGE_ADDR( t[0], 0, 0 ), 
 			VIPS_IMAGE_SIZEOF_IMAGE( t[0] ), 
-			png->fmt, flags )) ) {
+			png->fmt, 0 )) ) {
 			vips_error( class->nickname, 
 				"%s", spng_strerror( error ) ); 
 			return( -1 );
@@ -481,12 +486,10 @@ vips_foreign_load_png_load( VipsForeignLoad *load )
 		t[0] = vips_image_new();
 		vips_foreign_load_png_set_header( png, t[0] );
 
-		/* We can decode regular PNGs progressively.
+		/* Initialize for progressive decoding.
 		 */
-		flags |= SPNG_DECODE_PROGRESSIVE;
-
 		if( (error = spng_decode_image( png->ctx, NULL, 0, 
-			png->fmt, flags )) ) {
+			png->fmt, SPNG_DECODE_PROGRESSIVE )) ) {
 			vips_error( class->nickname, 
 				"%s", spng_strerror( error ) ); 
 			return( -1 );