Borderless window. How to add a shadow and remove 1px border?

Question

I need to create a borderless window with specified background color. I know how to remove a non client area and get something like this:

It's cool but not truly what I want. If you take a closer look at any aero window - there's a shadow around it (actually this is not a shadow but some glow). I found somewhere that I can use this code to add a shadow:

const MARGINS shadow_on = { 1, 1, 1, 1 };
DwmExtendFrameIntoClientArea(hwnd, &shadow_on);

It's almost do it's job (thought this is absolutely not clear to me - documentation says nothing about relationship of shadow and this function). Almost. There's a thin border appeared around the window. It looks like it's semitransparent and it breaks the look and feel of the window:

I know that it's possible - the visual studio even change the color of this border somehow!

Update: as IInspectable noticed in comments I can use negative margins in DwmExtendFrameIntoClientArea(). I set -1 value and got this result:

As you can see - it's even weirder. I tried to fill a background with color, but without luck.

Verbenia

You can clip the window area to remove the glow. Did You try to clip it already in order to remove the glow ? It might be, that You cannot get rid of the glow and use shadow at the same time. – Mita

@Mita no, you didn't understand - I need a glow - I don't need a border which appears when I'm adding a glow. – Verbenia

Then do not use the mentioned function. Draw it Yourself. One px lines, on all sides, with a slight ligther green. – Mita

If I'll not use this function there will be no glow at all - like in first screenshot. – Verbenia

DwmExtendFrameIntoClientArea: "Use negative margin values to create the "sheet of glass" effect where the client area is rendered as a solid surface with no window border." – Azazel

Why not use CS_DROPSHADOW in class style? – Precarious

@Azazel Unfortunately this didn't help - I updated a post with a new picture. – Verbenia

@BarmakShemirani This style gives a shadow on right side and bottom only - not aero shadow. – Verbenia

I see, calling DwmExtenFrameIntoClientArea with negative margin values turns the entire client area into Aero Glass. Have you tried using a margin with all members set to zero? – Azazel

Yes - that way there's no shadow (see first screenshot). – Verbenia

Wait I'm confused. What kind of shadow do you want? Could you produce a mockup of what you want to see? Is CS_DROPSHADOW not it? – Accelerometer

@Accelerometer What I wanted to achieve is called aero shadow - it's a glowing around window perimeter. CS_DROPSHADOW adds shadow near bottom and right window edges only. Anyway, I found how to achieve what I want: 1. CreateWindowEx with WS_EX_LAYERED flag. 2. call SetLayeredWindowAttributes(hWnd, RGB(0, 0, 0), 0, LWA_COLORKEY); - the color should differ from window's background (specified in WNDCLASSEX). 3. call DwmExtendFrameIntoClientArea() with margins where at least one margin not zero. – Verbenia

All right then. Glad to see you've found how to do it; good luck from here on out! – Accelerometer

@nikitablack: Could you add an answer to this question, showing a bit more detail like the window and class styles you're using. I'm unable to get the Aero shadow to appear on a WS_POPUP using the DwmExtendFrameIntoClientArea as you've shown (with or without the semi-transparent border). – Rodroda

@AdrianMcCarthy Unfortunately, I don't have a working example and I absolutely don't remember what I did. The only thing I remember is that visual studio (and other MS tools) used another windows for the shadow - that's how they managed to change it's color. Basically they add a new window on every edge and somehow rendered semitransparent glow. – Verbenia

Answer 1

To remove one pixel border after calling this function:

const MARGINS shadow_on = { 1, 1, 1, 1 };
DwmExtendFrameIntoClientArea(hwnd, &shadow_on);

You need to override WndProc WM_NCCALCSIZE message, and return 0 as the result. Also you need to create window using WS_CAPTION style. (On Windows XP this code won't produce rectangular window, but there is no shadow on WinXP, so on Windows XP you should fallback to WS_POPUP window style)
By the way, to add shadow it is enough to use this margins:
const MARGINS shadow_on = { 1, 0, 0, 0 };

Here is clean windows API code example how to create such window, it is written on Delphi: https://mcmap.net/q/1627046/-how-to-create-window-without-border-and-with-shadow-like-github-app

Heracles