png: add support for palettes with alpha values

DentonW · Aug 20, 2015 · c0e964d · c0e964d
1 parent adc5d93
commit c0e964d
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Showing 2 changed files with 33 additions and 23 deletions.
diff --git a/DevIL/include/IL/il.h b/DevIL/include/IL/il.h
@@ -374,7 +374,7 @@ typedef long long unsigned int ILuint64;
 #define IL_JPG_SAVE_FORMAT         0x0721
 #define IL_CHEAD_HEADER_STRING     0x0722
 #define IL_PCD_PICNUM              0x0723
-#define IL_PNG_ALPHA_INDEX 0x0724 //XIX : ILint : the color in the palette at this index value (0-255) is considered transparent, -1 for no trasparent color
+#define IL_PNG_ALPHA_INDEX 0x0724 // currently has no effect!
 #define IL_JPG_PROGRESSIVE         0x0725
 #define IL_VTF_COMP                0x0726
 

diff --git a/DevIL/src-IL/src/il_png.c b/DevIL/src-IL/src/il_png.c
@@ -8,10 +8,6 @@
 //
 // Description: Portable network graphics file (.png) functions
 //
-// 20040223 XIX : now may spit out pngs with a transparent index, this is mostly a hack
-// but the proper way of doing it would be to change the pal stuff to think in argb rather than rgb
-// which is something of a bigger job.
-//
 //-----------------------------------------------------------------------------
 
 // Most of the comments are left in this file from libpng's excellent example.c
@@ -495,11 +491,6 @@ ILboolean iSavePngInternal()
 	ILuint		BitDepth, i, j;
 	ILubyte 	**RowPtr = NULL;
 	ILimage 	*Temp = NULL;
-	ILpal		*TempPal = NULL;
-
-//XIX alpha
-	ILubyte		transpart[1];
-	ILint		trans;
 
 	if (iCurImage == NULL) {
 		ilSetError(IL_ILLEGAL_OPERATION);
@@ -603,19 +594,40 @@ ILboolean iSavePngInternal()
 			PNG_INTERLACE_NONE, PNG_COMPRESSION_TYPE_BASE, PNG_FILTER_TYPE_BASE);
 	}
 
+    // set the palette if there is one.  REQUIRED for indexed-color images.
 	if (iCurImage->Format == IL_COLOUR_INDEX) {
-		// set the palette if there is one.  REQUIRED for indexed-color images.
+	    ILpal		*TempPal = NULL;
+        ILint       palType;
+        ILint numCols;
+
+        numCols = ilGetInteger(IL_PALETTE_NUM_COLS);
+        if(numCols>256) {
+            numCols = 256;  // png maximum
+        }
+
 		TempPal = iConvertPal(&iCurImage->Pal, IL_PAL_RGB24);
-		png_set_PLTE(png_ptr, info_ptr, (png_colorp)TempPal->Palette,
-			ilGetInteger(IL_PALETTE_NUM_COLS));
-
-//XIX alpha
-		trans=iGetInt(IL_PNG_ALPHA_INDEX);
-		if ( trans>=0)
-		{
-			transpart[0]=(ILubyte)trans;
-			png_set_tRNS(png_ptr, info_ptr, transpart, 1, 0);
-		}
+		png_set_PLTE(png_ptr, info_ptr, (png_colorp)TempPal->Palette, numCols);
+        ilClosePal(TempPal);
+
+        palType = ilGetInteger(IL_PALETTE_TYPE);
+        if( palType==IL_PAL_RGBA32 || palType==IL_PAL_BGRA32 ) {
+            // the palette has transparency, so we need a tRNS chunk.
+            png_byte trans[256];    // png supports up to 256 palette entries
+            int maxTrans = -1;
+            int i;
+            for(i=0; i<numCols; ++i) {
+                ILubyte alpha = iCurImage->Pal.Palette[(4*i) + 3];
+                trans[i] = alpha;
+                if(alpha<255) {
+                    // record the highest non-opaque index
+                    maxTrans = i;
+                }
+            }
+            // only write tRNS chunk if we've got some non-opaque colours
+            if(maxTrans!=-1) {
+                png_set_tRNS(png_ptr, info_ptr, trans, maxTrans+1, 0);
+            }
+        }
 	}
 
 	/*
@@ -711,7 +723,6 @@ ILboolean iSavePngInternal()
 
 	if (Temp != iCurImage)
 		ilCloseImage(Temp);
-	ilClosePal(TempPal);
 
 	return IL_TRUE;
 
@@ -720,7 +731,6 @@ ILboolean iSavePngInternal()
 	ifree(RowPtr);
 	if (Temp != iCurImage)
 		ilCloseImage(Temp);
-	ilClosePal(TempPal);
 	return IL_FALSE;
 }