Replace global variables pixel_progress etc with Progress class

src/common.cpp

@@ -26,13 +26,13 @@ const std::vector<std::string> transforms = {"Channel_Compact", "YCoCg", "?? YCb
                                              "?? Other ??" };
 // Plenty of room for future extensions: transform "Other" can be used to encode identifiers of arbitrary many other transforms
 
-// Some global variables used to show progress and to know when to stop a partial/progressive decode
-// (TODO: avoid global variables)
-int64_t pixels_todo = 0;
-int64_t pixels_done = 0;
-int progressive_qual_target = 0;
-int progressive_qual_shown = -1;
-
+Progress::Progress()
+{
+    pixels_todo = 0;
+    pixels_done = 0;
+    progressive_qual_target = 0;
+    progressive_qual_shown = -1;
+}
 
 // The order in which the planes are encoded.
 // Lookback (animations-only, value refers to a previous frame) has to be first, because all other planes are not encoded if lookback != 0

src/common.hpp

@@ -33,11 +33,17 @@ limitations under the License.
 #include "io.hpp"
 
 
-extern int64_t pixels_todo;
-extern int64_t pixels_done;
-extern int progressive_qual_target;
-extern int progressive_qual_shown;
-
+// Variables used to show progress and to know when to stop a partial/progressive decode
+struct Progress
+{
+    Progress();
+    int64_t pixels_todo;
+    int64_t pixels_done;
+    int progressive_qual_target;
+    int progressive_qual_shown;
+    int quality() const { return (int)(10000 * pixels_done / pixels_todo); }
+    bool reached_target() const { return quality() >= progressive_qual_target; }
+};
 
 #define MAX_TRANSFORM 13
 #define MAX_PREDICTOR 2