fix bug with encoding transparent single-pixel image

3 files changed, 91 insertions, 4 deletions

diff --git a/lodepng.cpp b/lodepng.cpp
index 31f146d..81044eb 100644
--- a/lodepng.cpp
+++ b/lodepng.cpp
@@ -1,5 +1,5 @@
 /*
-LodePNG version 20140823
+LodePNG version 20141119
 
 Copyright (c) 2005-2014 Lode Vandevenne
 
@@ -37,7 +37,7 @@ Rename this file to lodepng.cpp to use it for C++, or to lodepng.c to use it for
 #include <fstream>
 #endif /*LODEPNG_COMPILE_CPP*/
 
-#define VERSION_STRING "20140823"
+#define VERSION_STRING "20141119"
 
 #if defined(_MSC_VER) && (_MSC_VER >= 1310) /*Visual Studio: A few warning types are not desired here.*/
 #pragma warning( disable : 4244 ) /*implicit conversions: not warned by gcc -Wall -Wextra and requires too much casts*/
@@ -3679,7 +3679,10 @@ unsigned lodepng_auto_choose_color(LodePNGColorMode* mode_out,
   if(error) return error;
   mode_out->key_defined = 0;
 
-  if(prof.key && w * h <= 16) prof.alpha = 1; /*too few pixels to justify tRNS chunk overhead*/
+  if(prof.key && w * h <= 16) {
+    prof.alpha = 1; /*too few pixels to justify tRNS chunk overhead*/
+    if(prof.bits < 8) prof.bits = 8; /*PNG has no alphachannel modes with less than 8-bit per channel*/
+  }
   grey_ok = !prof.colored && !prof.alpha; /*grey without alpha, with potentially low bits*/
   n = prof.numcolors;
   palettebits = n <= 2 ? 1 : (n <= 4 ? 2 : (n <= 16 ? 4 : 8));
diff --git a/lodepng.h b/lodepng.h
index 8e2e038..a934118 100644
--- a/lodepng.h
+++ b/lodepng.h
@@ -1,5 +1,5 @@
 /*
-LodePNG version 20140823
+LodePNG version 20141119
 
 Copyright (c) 2005-2014 Lode Vandevenne
 
diff --git a/lodepng_unittest.cpp b/lodepng_unittest.cpp
index 1e4a49c..150511c 100644
--- a/lodepng_unittest.cpp
+++ b/lodepng_unittest.cpp
@@ -476,6 +476,68 @@ void testOtherPattern2()
   doCodecTest(image1);
 }
 
+void testSinglePixel(int r, int g, int b, int a)
+{
+  std::cout << "codec single pixel " << r << " " << g << " " << b << " " << a << std::endl;
+  Image pixel;
+  pixel.width = 1;
+  pixel.height = 1;
+  pixel.colorType = LCT_RGBA;
+  pixel.bitDepth = 8;
+  pixel.data.resize(4);
+  pixel.data[0] = r;
+  pixel.data[1] = g;
+  pixel.data[2] = b;
+  pixel.data[3] = a;
+
+  doCodecTest(pixel);
+}
+
+void testColor(int r, int g, int b, int a)
+{
+  std::cout << "codec test color " << r << " " << g << " " << b << " " << a << std::endl;
+  Image image;
+  image.width = 100;
+  image.height = 100;
+  image.colorType = LCT_RGBA;
+  image.bitDepth = 8;
+  image.data.resize(100 * 100 * 4);
+  for(int y = 0; y < 100; y++)
+  for(int x = 0; x < 100; x++)
+  {
+    image.data[100 * 4 * y + 4 * x + 0] = r;
+    image.data[100 * 4 * y + 4 * x + 0] = g;
+    image.data[100 * 4 * y + 4 * x + 0] = b;
+    image.data[100 * 4 * y + 4 * x + 0] = a;
+  }
+
+  doCodecTest(image);
+
+  Image image2 = image;
+  image2.data[3] = 0; //one fully transparent pixel
+  doCodecTest(image2);
+  image2.data[3] = 128; //one semi transparent pixel
+  doCodecTest(image2);
+
+  Image image3 = image;
+  // add 255 different colors
+  for(int i = 0; i < 255; i++) {
+    image.data[i * 4 + 0] = i;
+    image.data[i * 4 + 1] = i;
+    image.data[i * 4 + 2] = i;
+    image.data[i * 4 + 3] = 255;
+  }
+  doCodecTest(image3);
+  // a 256th color
+  image.data[255 * 4 + 0] = 255;
+  image.data[255 * 4 + 1] = 255;
+  image.data[255 * 4 + 2] = 255;
+  image.data[255 * 4 + 3] = 255;
+  doCodecTest(image3);
+
+  testSinglePixel(r, g, b, a);
+}
+
 void testPNGCodec()
 {
   codecTest(1, 1);
@@ -487,6 +549,28 @@ void testPNGCodec()
 
   testOtherPattern1();
   testOtherPattern2();
+
+  testColor(255, 255, 255, 255);
+  testColor(0, 0, 0, 255);
+  testColor(1, 2, 3, 255);
+  testColor(255, 0, 0, 255);
+  testColor(0, 255, 0, 255);
+  testColor(0, 0, 255, 255);
+  testColor(0, 0, 0, 255);
+  testColor(1, 1, 1, 255);
+  testColor(1, 1, 1, 1);
+  testColor(0, 0, 0, 128);
+  testColor(255, 0, 0, 128);
+  testColor(127, 127, 127, 255);
+  testColor(128, 128, 128, 255);
+  testColor(127, 127, 127, 128);
+  testColor(128, 128, 128, 128);
+  //transparent single pixels
+  testColor(255, 0, 0, 0);
+  testColor(1, 2, 3, 0);
+  testColor(255, 255, 255, 0);
+  testColor(254, 254, 254, 0);
+  testColor(0, 0, 0, 0);
 }
 
 //Tests some specific color conversions with specific color bit combinations