display: Return error status from display::screenshot() instead of fi…

…le size

This makes it so errors in image::save_image() are printed to stderr
using our log facilities before returning, and also propagates the
function's result to screenshot()'s callers instead of a computed
screenshot size that doesn't hold true for PNG images.

Additionally, a couple of existing error messages have been reworded and
are now emitted through the log facilities instead of being sent
directly to stderr.

src/display.cpp

@@ -762,31 +762,32 @@ map_location display::minimap_location_on(int x, int y)
 	return loc;
 }
 
-int display::screenshot(std::string filename, bool map_screenshot)
+bool display::screenshot(const std::string& filename, bool map_screenshot)
 {
-	int size = 0;
+	bool res = false;
+
 	if (!map_screenshot) {
 		surface screenshot_surf = screen_.getSurface();
 
-		image::save_image(screenshot_surf, filename);
+		res = image::save_image(screenshot_surf, filename);
 
-		size = screenshot_surf->w * screenshot_surf->h;
+		if (!res) {
+			ERR_DP << "Screenshot failed: " << SDL_GetError() << '\n';
+		}
 	} else {
 		if (get_map().empty()) {
-			// Map Screenshot are big, abort and warn the user if he does strange things
-			std::cerr << "No map, can't do a Map Screenshot. If it was not wanted, check your hotkey.\n";
-			return -1;
+			ERR_DP << "No map loaded, cannot create a map screenshot.\n";
+			return false;
 		}
 
 		SDL_Rect area = max_map_area();
 		map_screenshot_surf_ = create_compatible_surface(screen_.getSurface(), area.w, area.h);
 
 		if (map_screenshot_surf_ == NULL) {
 			// Memory problem ?
-			std::cerr << "Can't create the screenshot surface. Maybe too big, try dezooming.\n";
-			return -1;
+			ERR_DP << "Could not create screenshot surface, try zooming out.\n";
+			return false;
 		}
-		size = map_screenshot_surf_->w * map_screenshot_surf_->h;
 
 		// back up the current map view position and move to top-left
 		int old_xpos = xpos_;
@@ -801,7 +802,14 @@ int display::screenshot(std::string filename, bool map_screenshot)
 		draw(true,true);
 
 		// finally save the image on disk
-		image::save_image(map_screenshot_surf_,filename);
+		res = image::save_image(map_screenshot_surf_,filename);
+
+		if (!res) {
+			// Need to do this ASAP or spurious messages result due to
+			// redraw_everything calling SDL too (e.g. "SDL_UpperBlit: passed
+			// a NULL surface")
+			ERR_DP << "Map screenshot failed: " << SDL_GetError() << '\n';
+		}
 
 		//NOTE: need to be sure that we free this huge surface (is it enough?)
 		map_screenshot_surf_ = NULL;
@@ -815,9 +823,7 @@ int display::screenshot(std::string filename, bool map_screenshot)
 		redraw_everything();
 	}
 
-	// convert pixel size to BMP size
-	size = (2048 + size*3);
-	return size;
+	return res;
 }
 
 gui::button* display::find_action_button(const std::string& id)

src/display.hpp

@@ -373,8 +373,8 @@ class display : public filter_context
 	/** Setter for the terrain code debug overlay on tiles */
 	void set_draw_terrain_codes(bool value) { draw_terrain_codes_ = value; }
 
-	/** Save a (map-)screenshot and return the estimated file size */
-	int screenshot(std::string filename, bool map_screenshot = false);
+	/** Save a (map-)screenshot and return whether the operation succeeded. */
+	bool screenshot(const std::string& filename, bool map_screenshot = false);
 
 	/** Invalidates entire screen, including all tiles and sidebar. Calls redraw observers. */
 	void redraw_everything();