A week of Apus Engine: a window that draws itself, and six small detective stories

[Cooler2]

58 commits this week, almost all of them on the border between the engine and the operating system, where a game stops being a picture in a rectangle and starts behaving like a proper desktop application.

A custom window frame
Drawing your own title bar is easy; doing it right is hard. The usual approach drops the frame entirely, and the window promptly forgets how to snap to screen edges, ignores Win+arrows and covers the taskbar when maximized. Apus Engine cuts the OS frame away but keeps the standard window style, so Windows itself still handles all of that. The same works under SDL.

On the game side it's one call: after BindToWindow, a regular TUIWindow becomes the frame of the OS window. Its top strip acts as the caption, and buttons and menus on it stay clickable. The new demo/WindowFrame shows it in action.

The window learns to talk to the system

• you can drop files into the window from the file manager;
• the clipboard pastes images, not just text;
• moving a window to a monitor with a different DPI gives the UI the right scale right away (it used to get the previous monitor's scale, and text grew twice);
• the mouse wheel under SDL no longer scrolls 120 times slower.

Text
Text effects have reached the UI: the TextFXStyle module adds glow, outline or shadow to a button caption with one style string. The effect can react to state, for example by glowing gold on hover.

Also, GetFont(50) at UI scale ×2 produced a glyph too tall for the cache, and one label could wipe out the whole scene frame. Not anymore.

Six small detective stories
Most of the week went into bugs that never show up in a demo but would ruin somebody's evening one day:

• The random number generator had PCG32's constants but a different algorithm. It is real PCG32 now.
• The UDP server silently listened on port+100 when its port was busy, and two clients started in the same second got the same session ID.
• SSE matrix multiply crashed or didn't depending on stack layout. Fixed, and slightly faster as a bonus.
• A network test failed once in a hundred runs: a stray #0 in an IP address sent the lookup to thread-unsafe gethostbyname.
• The "are we under a debugger" check on Linux made the parent process a debugger itself, and the test waited for Enter forever.
• Triangulating a polygon walked the other way looped forever.

Bottom line: a game on Apus Engine now behaves much more like a real application, and several bugs that would only have hit real players didn't make it to a release.