Rendering System

The rendering system is built around the CPixmap class, which wraps DirectDraw surface management. On non-Windows platforms, Free Direct provides SDL3-based implementations of the DirectDraw API.

CPixmap Overview

Header: include/pixmap.hpp
Source: src/pixmap.cpp (~1,922 lines)

CPixmap is the image surface manager. It allocates and manages 15 DirectDraw surfaces (one per channel), handles sprite blitting, and manages the display pipeline.

Resolution

The game renders at a fixed 640×480 pixel resolution:

Constant	Value	Description
`LXIMAGE`	640	Game window width (pixels)
`LYIMAGE`	480	Game window height (pixels)
`POSDRAWX`	0	Draw origin X
`POSDRAWY`	0	Draw origin Y

Image Channel System

CPixmap manages 15 independent render channels, each backed by a separate DirectDraw surface. Content is rendered into these channels and composited to produce the final frame.

Channel	Value	Content	Image File
`CHBACK`	0	Background terrain	`decor000–031.blp`
`CHOBJECT`	1	Foreground objects and pickups	`object.blp`
`CHBLUPI`	2	Default player character	`blupi000.blp`
`CHDECOR`	3	Decorative overlays	`decor000–031.blp`
`CHBUTTON`	4	UI buttons	`button.blp`
`CHJAUGE`	5	Gauge bar sprites	`jauge.blp`
`CHTEXT`	6	Normal text characters	`text.blp`
`CHLITTLE`	7	Small text characters	`littletxt.blp`
`CHMAP`	8	Minimap sprites	`map.blp`
`CHEXPLO`	9	Explosion sprites	`explo.blp`
`CHELEMENT`	10	Particle/element effects	`element.blp`
`CHBLUPI1`	11	Player variant 1 (multiplayer)	`blupi001.blp`
`CHBLUPI2`	12	Player variant 2 (multiplayer)	`blupi002.blp`
`CHBLUPI3`	13	Player variant 3 (multiplayer)	`blupi003.blp`
`CHTEMP`	14	Temporary scratch surface	—

Sprite Dimensions

Sprite Type	Width	Height	Constants
Objects (enemies, items, vehicles)	64 px	64 px	`DIMOBJX`, `DIMOBJY`
Player character (Blupi)	60 px	60 px	`DIMBLUPIX`, `DIMBLUPIY`
Explosions	128 px	128 px	`DIMEXPLOX`, `DIMEXPLOY`
UI Buttons	40 px	40 px	`DIMBUTTONX`, `DIMBUTTONY`
Gauge bars	124 px	22 px	`DIMJAUGEX`, `DIMJAUGEY`
Normal text characters	16 px max	16 px max	`DIMTEXTX`, `DIMTEXTY`
Small text characters	16 px max	12 px max	`DIMLITTLEX`, `DIMLITTLEY`

Render Pipeline

Each game tick, the rendering sequence is approximately:

CDecor::Build(rect) is called to render the game world
Terrain cells in the visible area are blitted from CHBACK
Moving objects are drawn from CHOBJECT, CHEXPLO, etc.
Player character is drawn from CHBLUPI
Decorative overlays from CHDECOR are applied
UI elements (buttons, gauges, text) from CHBUTTON, CHJAUGE, CHTEXT, CHLITTLE
Minimap drawn from CHMAP
Final composited frame blitted from backbuffer to primary surface
CPixmap::Display() presents the frame

Camera Scrolling

The camera scrolls to follow the player. Scrolling is triggered when the player approaches the screen edge:

Constant	Value	Description
`SCROLL_SPEED`	8	Camera scroll speed (pixels per tick)
`SCROLL_MARGX`	80	Horizontal scroll trigger margin (pixels from edge)
`SCROLL_MARGY`	40	Vertical scroll trigger margin (pixels from edge)

Color Depth Modes

The game supports both 8-bit palette and 16-bit true-color rendering, selected via the TrueColorBack and TrueColorDecor settings in config.def:

8-bit mode — uses gamefiles/IMAGE08/ assets
16-bit mode — uses gamefiles/IMAGE16/ assets (default)
jauge.blp and map.blp are always loaded from IMAGE08 (no 16-bit version)

Known Rendering Issues

⛔

Double Create() Issue

CPixmap::Create() is called twice during startup — once directly, and once inside CPixmap::CacheAll(TRUE, …). This is a likely decompilation artifact. Real DirectDraw may reject the second initialization. See Known Issues.

⚠️

Parameter Swap Bug

The bTrueColorBack and bTrueColorDecor parameters appear to be swapped between the declaration in pixmap.hpp and the definition in pixmap.cpp. This may produce incorrect behavior when the two color depth settings differ.

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