Use black border color in borderless fullscreen mode on Windows

[Calinou]

• Follow-up to [Windows] Use clear color for non exclusive fullscreen border, fix maximize for borderless window switching to exclusive fs. #82031.

This makes the border much less noticeable, or even completely invisible on OLED displays.

The gray border is still visible for a split second after starting a project configured to run in fullscreen (while the splash screen is still displayed). Any ideas on how to make it black as soon as possible? cc @bruvzg

• See Enabling fullscreen via code shows window border at screen edges (DisplayServer regression) #63500.

Preview

Example on the edges of an OLED display (LG C2 42"):

Before

After

[bruvzg]

The gray border is still visible for a split second after starting a project configured to run in fullscreen (while the splash screen is still displayed). Any ideas on how to make it black as soon as possible?

Probably related to the early BG erase:

godot/platform/windows/display_server_windows.cpp

Lines 3504 to 3522 in 87d40ba

	case WM_ERASEBKGND: {
	Color early_color;
	if (!_get_window_early_clear_override(early_color)) {
	break;
	}
	bool must_recreate_brush = !window_bkg_brush || window_bkg_brush_color != early_color.to_argb32();
	if (must_recreate_brush) {
	if (window_bkg_brush) {
	DeleteObject(window_bkg_brush);
	}
	window_bkg_brush = CreateSolidBrush(RGB(early_color.get_r8(), early_color.get_g8(), early_color.get_b8()));
	}
	HDC hdc = (HDC)wParam;
	RECT rect = {};
	if (GetUpdateRect(hWnd, &rect, true)) {
	FillRect(hdc, &rect, window_bkg_brush);
	}
	return 1;
	} break;

Maybe RedrawWindow should be called with RDW_FRAME flag when splash is displayed (not sure where exactly is the most appropriate place to do it) to force redraw the border. Or WM_ERASEBKGND should draw back border and fill only the client area if it's in full-screen.

[bruvzg]

This looks better, but I feel like we might still want to add another option for FS (see #63500 (comment)), in a non compatibility breaking manner, maybe something like:

• MODE_FULLSCREEN → (WS_OVERLAPPED | WS_BORDER + screen size), with black border.
• MODE_EXCLUSIVE_FULLSCREEN and BORDERLESS flag is not set → (WS_POPUP + screen size), always "exclusive".
• MODE_EXCLUSIVE_FULLSCREEN and BORDERLESS flag is set → (WS_OVERLAPPED + screen size), w/o border, might be "borderless" or "exclusive" depending on GPU.

[Calinou]

This looks better, but I feel like we might still want to add another option for FS (see #63500 (comment)), in a non compatibility breaking manner, maybe something like:

I agree it's good to have both modes available (as in, "best-effort borderless fullscreen" and "forced borderless fullscreen"). The proposed API should work well with existing projects as I'm not aware of any projects that enable both exclusive fullscreen and borderless at the same time currently.

[bruvzg]

but I feel like we might still want to add another option for FS

#88735

[bruvzg]

There's also mention of clear color in the WINDOW_MODE_FULLSCREEN documentation, which should be changed as well.

[alvinhochun]

• MODE_FULLSCREEN → (WS_OVERLAPPED | WS_BORDER + screen size), with black border.

If this is intended for the editor and to allow popup windows and menus to show properly, may I suggest an alternative? Don't use WS_BORDER. Instead make the window 1px taller, then subtract 1px from the viewport (leaving the bottom row of pixel unused), which should prevent drivers from forcing exclusive fullscreen but still having the window content match the screen size.

[bruvzg]

If this is intended for the editor and to allow popup windows and menus to show properly, may I suggest an alternative? Don't use WS_BORDER. Instead make the window 1px taller, then subtract 1px from the viewport (leaving the bottom row of pixel unused), which should prevent drivers from forcing exclusive fullscreen but still having the window content match the screen size.

That's what #88852 do (and the extra pixel is made transparent as well). But it should be tested on different vendor GPUs to make sure it's not affecting performance.