A DirectDraw game asks for an impossible mode, because its mode table overflowed

Symptoms

The game calls SetDisplayMode with a depth or size that no display has, such as 640 × 480 at 1,640 bits per pixel. The call fails with DDERR_UNSUPPORTED or DDERR_INVALIDMODE. The game then quits or shows an error about the video mode. The values on screen look like a mix of two variables.

Cause

The game's EnumDisplayModes callback copies every mode into a fixed table, with no limit. A 1997 display listed a dozen modes. A modern display, or Wine, lists hundreds. The table overflows into the variables after it (measured in POD: a 60-entry table at 0x6920b8 overwrote the desktop depth).

Evidence

WINEDEBUG=+ddraw shows the modes listed and the mode asked for. A breakpoint on the callback shows the right value on entry and the wrong one later.

What to do

Patch the callback so it keeps only modes the game can use (up to 1024 wide, at most as many as the table holds). Make it return "stop" once the table is full. A code cave in the code section's zero padding holds the new routine. Record it as a Deviation.

To find the table, start at the callback. Its address is an argument of the EnumDisplayModes call (IDirectDraw vtable slot 8). The callback stores to [table + index * size] with no compare.