Graphics

Game drawing code calls a table of driver entry points. MGRAPHIC.EXE implements MCGA/VGA drawing; EGA and Tandy have separate drivers. The loader installs far jumps in driver_slots from each driver’s header. The MCGA driver chapter describes its slots and data.

Pages

The MCGA driver uses 320-by-200 byte-per-pixel pages. Page 0 is the screen; allocated pages provide offscreen storage. Game code passes a struct page with the page number, origin, clipping bounds and text settings:

struct page {
    int number;
    int left, top, right, bottom;
    int active, colour;
    int text_colour;
    int font;
};

blit() copies rectangles between pages. sprite_draw() and its variants draw stored sprites. Game code assembles map tiles, cities, units and menus from those operations. Mouse visibility is managed around drawing through mouse_off() and mouse_on().

Page 2 also holds the map database. A page number therefore identifies storage, not necessarily a picture intended for display.

Video selection

SETUP.C offers VGA, MCGA, EGA and Tandy 1000. VGA and MCGA both select driver M. MGRAPHIC.ASM initializes BIOS mode 13h, a 320-by-200 display with 256 palette indices. This repository builds the M driver; the setup choices alone do not establish how the other drivers implement drawing.

Palette animation

PALETTE.INC implements set_cycle(), start_cycle() and stop_cycle(). FADE.INC implements fades. The MCGA driver writes palette values to the VGA DAC. Changing a palette entry changes the displayed colour of every pixel using that index without rewriting the pixels themselves.

Palette asset loading uses load_palette() in FILEIO.C, through the picture-loading path. A file named as a palette must not be assumed to be a headerless array of RGB values.