fix background color affecting page color (fixes #5521)

Author: kjk

src/SumatraPDF.cpp

@@ -2687,8 +2687,10 @@ static void RerenderFixedPage() {
 
 void UpdateDocumentColors() {
     COLORREF bg;
-    COLORREF text = ThemeDocumentColors(bg);
-    // logfa("retrieved doc colors in UpdateDocumentColors: 0x%x 0x%x\n", text, bg);
+    // use ThemePageRenderColors instead of ThemeDocumentColors
+    // so that engine-type background color settings (fixedPageUI.backgroundColor etc.)
+    // only affect the canvas/window background, not the PDF page rendering
+    COLORREF text = ThemePageRenderColors(bg);
 
     if ((text == gRenderCache->textColor) && (bg == gRenderCache->backgroundColor)) {
         return; // colors didn't change

src/SumatraStartup.cpp

@@ -1457,7 +1457,7 @@ int APIENTRY WinMain(_In_ HINSTANCE /*hInstance*/, _In_opt_ HINSTANCE, _In_ LPST
 
     gCrashOnOpen = flags.crashOnOpen;
 
-    gRenderCache->textColor = ThemeDocumentColors(gRenderCache->backgroundColor);
+    gRenderCache->textColor = ThemePageRenderColors(gRenderCache->backgroundColor);
     // logfa("retrieved doc colors in WinMain: 0x%x 0x%x\n", gRenderCache->textColor, gRenderCache->backgroundColor);
 
     gIsStartup = true;

src/Theme.cpp

@@ -358,6 +358,34 @@ COLORREF ThemeDocumentColors(COLORREF& bg, bool isEbook) {
     return text;
 }
 
+// colors for page bitmap recoloring (render cache)
+// only affected by invertColors / theme, not by engine-type background color settings
+// (those only affect the canvas/window background around the page)
+COLORREF ThemePageRenderColors(COLORREF& bg) {
+    COLORREF text = kColBlack;
+    bg = kColWhite;
+
+    if (!gGlobalPrefs->fixedPageUI.invertColors) {
+        return text;
+    }
+
+    // default colors
+    if (gCurrentTheme == gThemeLight) {
+        std::swap(text, bg);
+        return text;
+    }
+
+    // if we're inverting in non-default themes, the colors
+    // should match the colors of the window
+    text = ThemeWindowTextColor();
+    bg = ThemeMainWindowBackgroundColor();
+
+    if (gCurrThemeIndex < 3) {
+        bg = AccentColor(bg, 8);
+    }
+    return text;
+}
+
 COLORREF ThemeControlBackgroundColor() {
     // note: we can change it in ThemeUpdateAfterLoadSettings()
     auto col = GetThemeCol(gCurrentTheme->controlBackgroundColor, kRedColor);

src/Theme.h

@@ -7,6 +7,7 @@ void SelectNextTheme();
 void CreateThemeCommands();
 
 COLORREF ThemeDocumentColors(COLORREF&, bool isEbook = false);
+COLORREF ThemePageRenderColors(COLORREF&);
 COLORREF ThemeMainWindowBackgroundColor();
 COLORREF ThemeControlBackgroundColor();
 COLORREF ThemeWindowBackgroundColor();