Icon-O-Matic: Warn when exporting unsupported gradients to SVG

SVG does not support conic, diamond, xy, or sqrt_xy gradients.
Show a one time warning and export them as linear approximations.

Fixes #19533.

Change-Id: Id49d9ea098a47088c0865d5a8609b657b0bcc45b
Reviewed-on: https://review.haiku-os.org/c/haiku/+/9636
Reviewed-by: Zardshard Zardshard <[email protected]>
Tested-by: Commit checker robot <[email protected]>

src/apps/icon-o-matic/import_export/svg/SVGExporter.cpp

@@ -49,6 +49,7 @@ write_line(BPositionIO* stream, BString& string)
 // constructor
 SVGExporter::SVGExporter()
 	: Exporter(),
+	  fShownUnsupportedGradientWarning(false),
 	  fGradientCount(0),
 	  fOriginalEntry(NULL)
 {
@@ -156,6 +157,27 @@ SVGExporter::_DisplayWarning() const
 	return alert->Go() == 1;
 }
 
+// _DisplayUnsupportedGradientWarning
+void
+SVGExporter::_DisplayUnsupportedGradientWarning() const
+{
+	if (fShownUnsupportedGradientWarning)
+		return;
+
+	BAlert* alert = new BAlert(
+		B_TRANSLATE("SVG export"),
+		B_TRANSLATE("SVG does not support some gradient types "
+		            "(conic, diamond, xy, sqrt_xy).\n\n"
+		            "They will be exported as linear approximations and "
+		            "may look different in other viewers."),
+		B_TRANSLATE("OK")
+	);
+
+	alert->Go();
+	fShownUnsupportedGradientWarning = true;
+}
+
+
 // #pragma mark -
 
 // convert_join_mode_svg
@@ -368,6 +390,13 @@ SVGExporter::_ExportGradient(const Gradient* gradient, BPositionIO* stream)
 {
 	BString helper;
 
+	// display a warning if the gradient is unsupported
+	if (gradient->Type() == GRADIENT_CONIC
+		|| gradient->Type() == GRADIENT_DIAMOND
+		|| gradient->Type() == GRADIENT_XY
+		|| gradient->Type() == GRADIENT_SQRT_XY)
+		_DisplayUnsupportedGradientWarning();
+
 	// start new gradient tag
 	if (gradient->Type() == GRADIENT_CIRCULAR) {
 		helper << "  <radialGradient ";

src/apps/icon-o-matic/import_export/svg/SVGExporter.h

@@ -40,6 +40,7 @@ class SVGExporter : public Exporter {
 
  private:
 			bool				_DisplayWarning() const;
+			void				_DisplayUnsupportedGradientWarning() const;
 
 			status_t			_ExportShape(const Shape* shape,
 											 BPositionIO* stream);
@@ -52,6 +53,7 @@ class SVGExporter : public Exporter {
 										 char* string,
 										 BPositionIO* stream);
 
+			mutable bool		fShownUnsupportedGradientWarning;
  			int32				fGradientCount;
 			entry_ref*			fOriginalEntry;
 };