Make warning messages in color handling code easier to understand

svg-flatten/src/main.cpp

@@ -73,7 +73,7 @@ int main(int argc, char **argv) {
                 "Flip polarity of all output gerber primitives for --format gerber.",
                 0},
             {"flip_svg_color_interpretation", {"-i", "--svg-white-is-gerber-dark"},
-                "Flip polarity of SVG color interpretation. This affects only SVG primitives like paths and NOT embedded bitmaps. With -i: white -> silk there/\"dark\" gerber primitive.",
+                "Flip polarity of SVG color interpretation. This affects only SVG primitives like paths and NOT embedded bitmaps. With -i: white -> \"dark\" gerber primitive, i.e. silk or copper present, or mask absent.",
                 0},
             {"pattern_complete_tiles_only", {"--pattern-complete-tiles-only"},
                 "Break SVG spec by only rendering complete pattern tiles, i.e. pattern tiles that entirely fit the target area, instead of performing clipping.",

svg-flatten/src/out_sexp.cpp

@@ -92,7 +92,7 @@ void KicadSexpOutput::header_impl(d2p, d2p) {
 
 KicadSexpOutput &KicadSexpOutput::operator<<(GerberPolarityToken pol) {
     if (pol == GRB_POL_CLEAR) {
-        cerr << "Warning: clear polarity not supported since KiCAD manages to have an even worse graphics model than gerber, except it can't excuse itself by its age..... -.-" << endl;
+        cerr << "Warning: Some shapes in this file were interpreted by svg-flatten as gerber \"clear\" polarity (background color). KiCad does not support clear polarity. Thus, these shapes will be omitted in the S-Expression output." << endl;
     }
 
     return *this;

svg-flatten/src/svg_color.cpp

@@ -64,6 +64,10 @@ enum gerber_color gerbolyze::svg_color_to_gerber(string color, string opacity, e
 
         if (alpha < 0.5f) {
             //cerr << "  -> none" << endl;
+            if (alpha > 0.01) {
+                cerr << "Info: Found an object with opacity set to " << alpha << ". This object will be omitted from the output." << endl; 
+            }
+
             return GRB_NONE;
         }
 
@@ -74,6 +78,10 @@ enum gerber_color gerbolyze::svg_color_to_gerber(string color, string opacity, e
             //cerr << "  -> dark" << endl;
             return GRB_DARK;
         }
+
+        if (hsv.v >= 0.4 && hsv.v <= 0.6) {
+            cerr << "Warning: color \"" << color << "\" is ambiguous. Gerbolyze decides whether to map colors to clear or dark polarity by checking if their HSV value (i.e. brightness) is above 50 %. This color has a value of " << hsv.v << ", close to 50 %." << endl; 
+        }
     }
 
     //cerr << "  -> dark" << endl;