COMMON: Added compilation safeguards for the png decoder

graphics/png.cpp

@@ -21,6 +21,9 @@
  */
 
 #include "graphics/png.h"
+
+#ifdef GRAPHICS_PNG_H
+
 #include "graphics/pixelformat.h"
 #include "graphics/surface.h"
 
@@ -489,3 +492,5 @@ void PNG::readTransparencyChunk(uint32 chunkLength) {
 }
 
 } // End of Graphics namespace
+
+#endif // GRAPHICS_PNG_H

graphics/png.h

@@ -23,8 +23,20 @@
 /*
  * PNG decoder used in engines:
  *  - sword25
+ * Dependencies:
+ *  - zlib
  */
 
+// Currently, only the sword25 engine uses the PNG decoder, so skip compiling
+// it if sword25 is not enabled, or if zlib (a required dependency) is not
+// enabled.
+
+#if !(defined(ENABLE_SWORD25) || defined(USE_ZLIB))
+
+// Do not compile the PNG decoder code
+
+#else
+
 #ifndef GRAPHICS_PNG_H
 #define GRAPHICS_PNG_H
 
@@ -164,3 +176,5 @@ private:
 } // End of Graphics namespace
 
 #endif // GRAPHICS_PNG_H
+
+#endif // Engine and zlib guard