Calculate fade based on frame level time

This makes the frame lenght FPS independant and fixes #459

Source/palette.cpp

@@ -167,7 +167,6 @@ void SetFadeLevel(DWORD fadeval)
 			system_palette[i].peGreen = (fadeval * logical_palette[i].peGreen) >> 8;
 			system_palette[i].peBlue = (fadeval * logical_palette[i].peBlue) >> 8;
 		}
-		Sleep(3);
 		palette_update();
 
 		// Workaround for flickering mouse in caves https://github.com/diasurgical/devilutionX/issues/7
@@ -185,7 +184,8 @@ void PaletteFadeIn(int fr)
 	int i;
 
 	ApplyGamma(logical_palette, orig_palette, 256);
-	for (i = 0; i < 256; i += fr) {
+	DWORD tc = SDL_GetTicks();
+	for (i = 0; i < 256; i = (SDL_GetTicks() - tc) / 1.875) { // 1000ms / 60 * 32
 		SetFadeLevel(i);
 	}
 	SetFadeLevel(256);
@@ -198,7 +198,8 @@ void PaletteFadeOut(int fr)
 	int i;
 
 	if (sgbFadedIn) {
-		for (i = 256; i > 0; i -= fr) {
+		DWORD tc = SDL_GetTicks();
+		for (i = 256; i > 0; i = 256 - (SDL_GetTicks() - tc) / 1.875) { // 1000ms / 60 * 32
 			SetFadeLevel(i);
 		}
 		SetFadeLevel(0);

SourceX/DiabloUI/diabloui.cpp

@@ -500,12 +500,16 @@ void LoadBackgroundArt(const char *pszFile)
 	ApplyGamma(logical_palette, orig_palette, 256);
 }
 
-void UiFadeIn(int steps)
+void UiFadeIn()
 {
+	static DWORD tc;
+	if (fadeValue == 0 && tc == 0)
+		tc = SDL_GetTicks();
 	if (fadeValue < 256) {
-		fadeValue += steps;
+		fadeValue = (SDL_GetTicks() - tc) / 1.875; // 1000ms / 60 * 32
 		if (fadeValue > 256) {
 			fadeValue = 256;
+			tc = 0;
 		}
 	}
 

SourceX/DiabloUI/diabloui.h

@@ -39,7 +39,7 @@ constexpr size_t size(T (&)[N])
 extern void (*gfnSoundFunction)(char *file);
 
 bool IsInsideRect(const SDL_Event &event, const SDL_Rect &rect);
-void UiFadeIn(int steps = 16);
+void UiFadeIn();
 bool UiFocusNavigation(SDL_Event *event);
 bool UiItemMouseEvents(SDL_Event *event, UiItem *items, std::size_t size);
 int GetCenterOffset(int w, int bw = 0);