Rewrite restoreDimensions to account for mismatched CSS/device pixel sizes.

This resolves the situation where the device pixels per css px does not match the screen DPI.
In that case, the restored width and height would be adjusted if the window width (css px)
would be larger than the screen width (dev pixels). This patch converts everything to css px
before checking if the dimensions fit the screen.

This resolves #411.

1 files changed, 51 insertions, 19 deletions

diff --git a/application/palemoon/components/sessionstore/SessionStore.jsm b/application/palemoon/components/sessionstore/SessionStore.jsm
index 4f95f10a71..c5e55321c2 100644
--- a/application/palemoon/components/sessionstore/SessionStore.jsm
+++ b/application/palemoon/components/sessionstore/SessionStore.jsm
@@ -3598,38 +3598,70 @@ var SessionStoreInternal = {
     var _this = this;
     function win_(aName) { return _this._getWindowDimension(win, aName); }
 
-    // find available space on the screen where this window is being placed
+    // Find available space on the screen where this window is being placed
     let screen = gScreenManager.screenForRect(aLeft, aTop, aWidth, aHeight);
     if (screen && !this._prefBranch.getBoolPref("sessionstore.exactPos")) {
       let screenLeft = {}, screenTop = {}, screenWidth = {}, screenHeight = {};
       screen.GetAvailRectDisplayPix(screenLeft, screenTop, screenWidth, screenHeight);
-      // constrain the dimensions to the actual space available
-      if (aWidth > screenWidth.value) {
-        aWidth = screenWidth.value;
+
+      // Screen X/Y are based on the origin of the screen's desktop-pixel coordinate space
+      let screenLeftCss = screenLeft.value;
+      let screenTopCss = screenTop.value;
+      
+      // Convert the screen's device pixel dimensions to CSS px dimensions
+      screen.GetAvailRect(screenLeft, screenTop, screenWidth, screenHeight);
+      let cssToDevScale = screen.defaultCSSScaleFactor;
+      let screenRightCss = screenLeftCss + screenWidth.value / cssToDevScale;
+      let screenBottomCss = screenTopCss + screenHeight.value / cssToDevScale;
+      
+      // Pull the window within the screen's bounds.
+      // First, ensure the left edge is on-screen
+      if (aLeft < screenLeftCss) {
+        aLeft = screenLeftCss;
       }
-      if (aHeight > screenHeight.value) {
-        aHeight = screenHeight.value;
+      // Then check the resulting right edge, and reduce it if necessary.
+      let right = aLeft + aWidth;
+      if (right > screenRightCss) {
+        right = screenRightCss;
+        // See if we can move the left edge leftwards to maintain width.
+        if (aLeft > screenLeftCss) {
+          aLeft = Math.max(right - aWidth, screenLeftCss);
+        }
       }
-      // and then pull the window within the screen's bounds
-      if (aLeft < screenLeft.value) {
-        aLeft = screenLeft.value;
-      } else if (aLeft + aWidth > screenLeft.value + screenWidth.value) {
-        aLeft = screenLeft.value + screenWidth.value - aWidth;
+      // Finally, update aWidth to account for the adjusted left and right edges.
+      aWidth = right - aLeft;
+
+      // Do the same in the vertical dimension.
+      // First, ensure the top edge is on-screen
+      if (aTop < screenTopCss) {
+        aTop = screenTopCss;
       }
-      if (aTop < screenTop.value) {
-        aTop = screenTop.value;
-      } else if (aTop + aHeight > screenTop.value + screenHeight.value) {
-        aTop = screenTop.value + screenHeight.value - aHeight;
+      // Then check the resulting right edge, and reduce it if necessary.
+      let bottom = aTop + aHeight;
+      if (bottom > screenBottomCss) {
+        bottom = screenBottomCss;
+        // See if we can move the top edge upwards to maintain height.
+        if (aTop > screenTopCss) {
+          aTop = Math.max(bottom - aHeight, screenTopCss);
+        }
       }
+      // Finally, update aHeight to account for the adjusted top and bottom edges.
+      aHeight = bottom - aTop;
     }
 
-    // only modify those aspects which aren't correct yet
-    if (aWidth && aHeight && (aWidth != win_("width") || aHeight != win_("height"))) {
-      aWindow.resizeTo(aWidth, aHeight);
-    }
+    // Only modify those aspects which aren't correct yet
     if (!isNaN(aLeft) && !isNaN(aTop) && (aLeft != win_("screenX") || aTop != win_("screenY"))) {
       aWindow.moveTo(aLeft, aTop);
     }
+    if (aWidth && aHeight && (aWidth != win_("width") || aHeight != win_("height"))) {
+      // Don't resize the window if it's currently maximized and we would
+      // maximize it again shortly after.
+      if (aSizeMode != "maximized" || win_("sizemode") != "maximized") {
+        aWindow.resizeTo(aWidth, aHeight);
+      }
+    }
+    
+    // Restore window state
     if (aSizeMode && win_("sizemode") != aSizeMode)
     {
       switch (aSizeMode)