Removed screenshot caching from Selector

The way the caching was implemented was rather problematic. Also I'm
not convinced caching is useful at all. So I removed it. If at some
point we decide that caching is a good idea, it would be best to
re-implement it from scratch, so nothing of value is lost by removing
the existing caching code.

One problem was that the prepare method would check the existence of
a screenshot file for every file in the directory, which adds to the
noticable delay before showing a directory which holds many files.

Another problem is there was no upper limit to the number of
screenshots that would be cached. On directories with many screenshots
the memory use could rise to several hundred megabytes, which can be
problematic on some of the systems we want to support.

Also there was a rather nasty hack present to ensure screenshots were
loaded without an alpha channel.

My main doubt about the usefulness of screenshot caching is that
caching will only speed up the showing of an image from the second
time onwards. In typical use, the average screenshot is displayed at
most once. If the image load time is long enough to annoy the user,
any real solution would have to work also for the first showing.
For example, background (asynchronous) loading could be implemented.

src/selector.cpp

@@ -85,13 +85,13 @@ int Selector::exec(int startSelection) {
 	unsigned int firstElement = 0;
 	unsigned int selected = constrain(startSelection, 0, fl.size() - 1);
 
-	vector<string> screens, titles;
+	vector<string> titles;
-	prepare(&fl,&screens,&titles);
+	prepare(&fl,&titles);
 
-	//Add the folder icon manually to be sure to load it with alpha support since we are going to disable it for screenshots
+	auto folderIcon = gmenu2x->sc.skinRes("imgs/folder.png");
-	if (gmenu2x->sc.skinRes("imgs/folder.png")==NULL)
+	if (!folderIcon) {
-		gmenu2x->sc.addSkinRes("imgs/folder.png");
+		folderIcon = gmenu2x->sc.addSkinRes("imgs/folder.png");
-	gmenu2x->sc.defaultAlpha = false;
+	}
 
 	bool close = false, result = true;
 	while (!close) {
@@ -105,9 +105,10 @@ int Selector::exec(int startSelection) {
 			firstElement = selected;
 
 		//Screenshot
-		if (selected-fl.dirCount()<screens.size()
+		if (fl.isFile(selected)) {
-				&& !screens[selected-fl.dirCount()].empty()) {
+			string& noext = titles[selected - fl.dirCount()];
-			Surface *screenshot = gmenu2x->sc[screens[selected-fl.dirCount()]];
+			string path = screendir + noext + ".png";
+			auto screenshot = OffscreenSurface::loadImage(path, "", false);
 			if (screenshot) {
 				screenshot->blitRight(s, 320, 0, 320, 240, 128u);
 			}
@@ -124,7 +125,7 @@ int Selector::exec(int startSelection) {
 					&& i < firstElement + nb_elements; i++) {
 			iY = i-firstElement;
 			if (fl.isDirectory(i)) {
-				gmenu2x->sc["imgs/folder.png"]->blit(s, 4, top + (iY * fontheight));
+				folderIcon->blit(s, 4, top + (iY * fontheight));
 				gmenu2x->font->write(s, fl[i], 21,
 							top + (iY * fontheight) + (fontheight / 2),
 							Font::HAlignLeft, Font::VAlignMiddle);
@@ -185,7 +186,7 @@ int Selector::exec(int startSelection) {
 						dir = dir.substr(0,p+1);
 						selected = 0;
 						firstElement = 0;
-						prepare(&fl,&screens,&titles);
+						prepare(&fl,&titles);
 					}
 				}
 				break;
@@ -202,7 +203,7 @@ int Selector::exec(int startSelection) {
 
 					selected = 0;
 					firstElement = 0;
-					prepare(&fl,&screens,&titles);
+					prepare(&fl,&titles);
 				}
 				break;
 
@@ -211,19 +212,14 @@ int Selector::exec(int startSelection) {
 		}
 	}
 
-	gmenu2x->sc.defaultAlpha = true;
-	freeScreenshots(&screens);
-
 	return result ? (int)selected : -1;
 }
 
-void Selector::prepare(FileLister *fl, vector<string> *screens, vector<string> *titles) {
+void Selector::prepare(FileLister *fl, vector<string> *titles) {
 	fl->setPath(dir);
-	freeScreenshots(screens);
-	screens->resize(fl->getFiles().size());
 	titles->resize(fl->getFiles().size());
 
-	string screendir = dir;
+	screendir = dir;
 	if (!screendir.empty() && screendir[screendir.length() - 1] != '/') {
 		screendir += "/";
 	}
@@ -237,19 +233,5 @@ void Selector::prepare(FileLister *fl, vector<string> *screens, vector<string> *
 		if (pos!=string::npos && pos>0)
 			noext = noext.substr(0, pos);
 		titles->at(i) = noext;
-
-		DEBUG("Searching for screen '%s%s.png'\n", screendir.c_str(), noext.c_str());
-
-		if (fileExists(screendir+noext+".png"))
-			screens->at(i) = screendir+noext+".png";
-		else
-			screens->at(i) = "";
-	}
-}
-
-void Selector::freeScreenshots(vector<string> *screens) {
-	for (uint i=0; i<screens->size(); i++) {
-		if (!screens->at(i).empty())
-			gmenu2x->sc.del(screens->at(i));
 	}
 }

src/selector.h

@@ -34,11 +34,9 @@ class Selector : protected Dialog {
 private:
 	int selRow;
 	LinkApp *link;
-	std::string file, dir;
+	std::string file, dir, screendir;
 
-	void prepare(FileLister *fl, std::vector<std::string> *screens,
+	void prepare(FileLister *fl, std::vector<std::string> *titles);
-			std::vector<std::string> *titles);
-	void freeScreenshots(std::vector<std::string> *screens);
 
 public:
 	Selector(GMenu2X *gmenu2x, LinkApp *link,