Graphics and Palette Rendering

Logical display

The game renders into a 320-by-200 array of eight-bit palette indexes. The active palette maps those indexes to 256 RGB colors. A host renderer MAY use a texture, bitmap, software surface, or GPU pipeline, but scene coordinates and hit targets always remain in logical pixels.

The final image SHOULD be scaled without filtering. Aspect correction is a presentation option; it MUST NOT alter logical hit testing.

The DOS presentation surface is 640 by 400: each indexed scene pixel occupies a 2-by-2 output block. Modal glyphs are seven logical pixels high, each source pixel is likewise expanded to a 2-by-2 output block, and successive text rows have an eight-logical-pixel (16-output-pixel) pitch. A host MAY produce the same relationship by composing at 640 by 400 or by another equivalent scaling pipeline. Pointer coordinates over the doubled scene MUST be converted back to the 320-by-200 scene coordinate system, while modal text-row hit testing uses the composed panel geometry.

PAL resources

A PAL member is exactly 768 bytes: 256 consecutive red, green, blue triplets. Every component is in the range 0 through 63. There is no header.

To produce an eight-bit host component while preserving both endpoints, use:

component8 = (component6 << 2) | (component6 >> 4)

Loading a palette replaces all 256 base entries. Scene effects may subsequently modify a range. The engine MUST retain an editable current palette rather than re-reading the immutable resource for every frame.

ART resources

An ART member begins with an array of 12-byte frame descriptors:

There is no explicit frame count. The first descriptor’s pixel offset marks the end of the descriptor array, so:

frame_count = first_pixel_offset / 12

Each frame owns exactly width * height row-major palette indexes. Pixel blocks are contiguous in descriptor order and fill the remainder of the member without padding. A parser MUST require a nonzero descriptor count, 12-byte table alignment, in-range offsets, contiguous blocks, and an exact end at resource length.

Origins are signed anchor adjustments, not necessarily absolute screen positions. A sprite may therefore begin left or above its logical entity coordinate.

Drawing modes

The scene runtime supplies frame number, loaded-art slot, X, Y, 8.8 scale, and render flags. Frame numbers in display records are one-based; zero suppresses drawing. The renderer subtracts one before indexing an ART descriptor.

Two drawing modes are required:

• opaque: copy every source index, including zero;
• transparent-zero: skip writes for source index zero.

Render-flag bits 0 and 1 flip the two image axes. Scaling uses 0x0100 as native size, but the stored word is an inverse 8.8 divisor rather than a magnification factor. For each axis the reference renderer computes:

scaled_size   = trunc(source_size * 256 / scale)
scaled_origin = trunc(signed_origin * 256 / scale)

Thus 0x0200 draws at half size and 0x0080 draws at double size. A zero scale, or a scale large enough to reduce either dimension to zero, suppresses the render slot. Division of a negative origin truncates toward zero.

Without reflection, the destination origin is anchor + scaled_origin. Reflection also reflects the signed origin about the supplied anchor:

normal_left    = anchor_x + scaled_origin_x
reflected_left = anchor_x - scaled_origin_x - scaled_width
normal_top     = anchor_y + scaled_origin_y
reflected_top  = anchor_y - scaled_origin_y - scaled_height

The renderer then reverses the corresponding source axis and clips to the logical viewport. Applying the normal origin formula before merely reversing the pixels is incorrect. LOGO.BIN depends on this distinction: its left dome half is frame 4 reflected about X=303.

Composition and display records

Every display definition reserves a stable render slot in the mixed display list. Direct-object, animation, and scene-thread controllers update their own reserved slots even though their update routines run separately. Final scene composition paints the active slots in increasing display-list order; it MUST NOT regroup them by controller family. A later direct scenery record can therefore occlude an earlier animation or moving actor.

LOGO.BIN relies on this rule for its oval aperture. Its moving RUN.ART actor uses an earlier display slot than three direct dome and bridge pieces. Those later pieces cover the actor while it enters from the left and exits to the right. This is ordinary display-list occlusion, not a geometric ellipse clip operation.

Direct entries select an art slot with the low seven bits of their slot byte. Slot bit 7 hides the entry. An entry with a hidden slot or frame zero does not draw.

Animation entries obtain the same frame, art, position, scale, and flip values from the current nine-byte animation step. UI overlays, text, and the pointer are drawn by their active interface after scene composition. The pointer mask specified in Input and user interface is the final framebuffer layer.

Font styles

STUFF.ART frame 0 stores the three-valued proportional font atlas. Text rendering maps source values 0, 1, and 2 through one of ten palette-index triplets:

1:  1,  7,  3    2:  1, 37,  4
3: 16, 15, 17    4: 15, 84, 84
5:  0, 64, 70    6:  0, 32, 37
7: 15, 86, 90    8: 15, 74, 69
9: 15, 32, 36   10: 15,  1,  8

The Computer Bible encounter prompt uses style 7 for L cyber-lie text, style 9 for P paraphrases, and style 10 for * victim-conversation text.

Palette operations

Scene programs can:

• replace the complete palette;
• fill an inclusive signed palette-adjustment range from a script variable;
• advance a signed phase and rotate an inclusive palette range;
• schedule palette updates; and
• start a blackout effect before a transition.

Range endpoints are inclusive. The rotate operation wraps its phase within the selected range. A blackout makes the next palette update all black and advances the effect’s countdown. Palette changes SHOULD be applied at frame boundaries to avoid partially updated presentation.

The F10 quick-save path uses a one-update blackout without a scene transition. It presents the existing indexed framebuffer through an all-black palette, then restores the current scene palette on the following update.

Text and UI graphics

Dialogue frames, action labels, maps, status icons, and most large UI elements are ordinary artwork or scene-driven compositions. Text strings are CP437.

STUFF.ART frame 0 is the shipped proportional font atlas. It is 257 by 14 pixels and contains two seven-row strips. It uses only source values 0, 1, and 2; the text style maps those values to three current-palette indexes. Glyphs cover bytes 21h through 7Fh. Glyph 21h starts at atlas offset zero. Each subsequent glyph begins after the preceding glyph’s width plus one pixel. At glyph index 40h (byte 61h, lowercase a) the offset resets to the start of atlas row 7. Space and control bytes draw nothing and advance three logical pixels.

The executable supplies these 95 glyph widths, in byte order 21h through 7Fh:

1 3 5 5 5 1 1 2 2 5 3 2 3 1 3 4
3 3 3 3 4 4 3 4 4 1 2 3 3 3 4 4
4 4 4 4 3 3 4 4 3 4 4 3 5 4 4 4
4 4 4 3 4 5 5 5 5 3 0 0 0 0 0 0
4 4 4 4 4 4 4 4 1 4 4 1 5 4 4 4
4 4 4 3 4 5 5 5 4 3 0 0 0 0 0

The destination advance for a printable glyph is its width plus one logical pixel. Wrapping MUST measure those proportional advances against the logical wrap-width byte, not count fixed character cells. All seven source rows and all three mapped source values are drawn; source value zero is a style color, not transparency.

The recovered text-style triplets are:

Ordinary Captain Bible and character dialogue uses style 2, adversary dialogue uses style 7, unselected choice rows use style 1, and the selected choice uses style 2.

Action captions are also shipped artwork. In STUFF.ART, frame 28 is SELECT and frame 29 is CONTINUE; their descriptors are respectively (-12,-3,24,7) and (-17,-3,35,7). The frame origin is applied to the label anchor, source index zero is transparent, and every retained source pixel is expanded to the same 2-by-2 output block as other logical artwork. A shipped-game implementation MUST use this atlas, width table, style mapping, and label artwork rather than a host or BIOS font.

The persistent status row is drawn from the same resource: Computer Bible is frame 4, Map is frame 32, the five Faith states are frames 22 through 26, the five acquired-power icons are frames 17 through 21, and the upper-right disk indicator is frame 11. Their positive descriptor origins are absolute logical screen placements when drawn with anchor (0,0).