IntFancyButton: Add buttonBackgroundEmpty option

data/base/images/intfac.img

@@ -444,3 +444,5 @@
 0,0,image_specstatsup.png
 0,0,image_volume_up.png
 0,0,image_volume_mute.png
+0,0,image_but_empty_up.png
+0,0,image_but_empty_down.png

src/intdisplay.cpp

@@ -938,14 +938,24 @@ bool intInitialiseGraphics()
 // Clear a button bitmap. ( copy the button background ).
 void IntFancyButton::displayClear(int xOffset, int yOffset)
 {
-	if (isDown())
-	{
-		iV_DrawImage(IntImages, IMAGE_BUT0_DOWN + buttonType * 2, xOffset + x(), yOffset + y());
-	}
-	else
+	UWORD buttonId = 0;
+	switch (buttonType)
 	{
-		iV_DrawImage(IntImages, IMAGE_BUT0_UP + buttonType * 2, xOffset + x(), yOffset + y());
+		case IntFancyButton::ButtonType::TOPBUTTON:
+			if (buttonBackgroundEmpty)
+			{
+				buttonId = (isDown() ? IMAGE_BUT_EMPTY_DOWN : IMAGE_BUT_EMPTY_UP);
+			}
+			else
+			{
+				buttonId = (isDown() ? IMAGE_BUT0_DOWN : IMAGE_BUT0_UP);
+			}
+			break;
+		case IntFancyButton::ButtonType::BTMBUTTON:
+			buttonId = (isDown() ? IMAGE_BUTB0_DOWN : IMAGE_BUTB0_UP);
+			break;
 	}
+	iV_DrawImage(IntImages, buttonId, xOffset + x(), yOffset + y());
 }
 
 // Create a button by rendering an IMD object into it.

src/intdisplay.h

@@ -141,6 +141,7 @@ class IntFancyButton : public W_CLICKFORM
 		int rate;
 	} model;
 	ButtonType buttonType;  // TOPBUTTON is square, BTMBUTTON has a little up arrow.
+	bool buttonBackgroundEmpty = false;
 };
 
 class IntObjectButton : public IntFancyButton

src/intfac.h

@@ -477,7 +477,9 @@ enum INTFAC_TYPE
 	IMAGE_SPECSTATS_DOWN,
 	IMAGE_SPECSTATS_UP,
 	IMAGE_INTFAC_VOLUME_UP,
-	IMAGE_INTFAC_VOLUME_MUTE
+	IMAGE_INTFAC_VOLUME_MUTE,
+	IMAGE_BUT_EMPTY_UP,
+	IMAGE_BUT_EMPTY_DOWN,
 };
 
 #endif //__INCLUDED_SRC_INTFAC_H__