Fix to compile without JPEG library.

Author: Sakari369

src/Canvas.cc

@@ -282,6 +282,7 @@ static void parsePNGArgs(Local<Value> arg, PngClosure& pngargs) {
   }
 }
 
+#ifdef HAVE_JPEG
 static void parseJPEGArgs(Local<Value> arg, JpegClosure& jpegargs) {
   // "If Type(quality) is not Number, or if quality is outside that range, the
   // user agent must use its default quality value, as if the quality argument
@@ -311,6 +312,7 @@ static void parseJPEGArgs(Local<Value> arg, JpegClosure& jpegargs) {
     }
   }
 }
+#endif
 
 static uint32_t getSafeBufSize(Canvas* canvas) {
   // Don't allow the buffer size to exceed the size of the canvas (#674)

src/closure.cc

@@ -1,5 +1,7 @@
 #include "closure.h"
 
+#ifdef HAVE_JPEG
+
 void JpegClosure::init_destination(j_compress_ptr cinfo) {
   JpegClosure* closure = (JpegClosure*)cinfo->client_data;
   closure->vec.resize(PAGE_SIZE);
@@ -21,3 +23,5 @@ void JpegClosure::term_destination(j_compress_ptr cinfo) {
   size_t finalSize = closure->vec.size() - closure->jpeg_dest_mgr->free_in_buffer;
   closure->vec.resize(finalSize);
 }
+
+#endif

src/closure.h

@@ -3,7 +3,11 @@
 #pragma once
 
 #include "Canvas.h"
+
+#ifdef HAVE_JPEG
 #include <jpeglib.h>
+#endif
+
 #include <nan.h>
 #include <png.h>
 #include <stdint.h> // node < 7 uses libstdc++ on macOS which lacks complete c++11
@@ -52,6 +56,7 @@ struct PngClosure : Closure {
   PngClosure(Canvas* canvas) : Closure(canvas) {};
 };
 
+#ifdef HAVE_JPEG
 struct JpegClosure : Closure {
   uint32_t quality = 75;
   uint32_t chromaSubsampling = 2;
@@ -73,3 +78,4 @@ struct JpegClosure : Closure {
     delete jpeg_dest_mgr;
   }
 };
+#endif