Rendering

Image Channels (CPixmap)

CPixmap manages a set of named channels (0–14), each holding one .blp image with its own palette and icon set.

// Load an image into a channel:
pPixmap->Cache(channel, "image/blupi.blp");

// Draw an icon from a channel:
pPixmap->DrawIcon(hdc, channel, icon, x, y);

Channel Reference

Constant	Value	Image file	Contents
`CHBACK`	0	various (phase background)	Current screen background
`CHFLOOR`	1	`floor000–003.blp`	Floor tiles (region 0–3)
`CHOBJECT`	2	`obj000–003.blp`	Objects — lower part (region 0–3)
`CHOBJECTo`	3	`obj-o000–003.blp`	Objects — upper overlay (region 0–3)
`CHBLUPI`	4	`blupi.blp`	All animation frames: Blupi + all enemies
`CHHILI`	5	`hili.blp`	Selection / action highlight overlays
`CHFOG`	6	`fog.blp`	15 fog-of-war tile patterns
`CHMASK1`	7	`mask1.blp`	Alpha mask for Blupi sprite blending
`CHLITTLE`	8	`little.blp`	Small pixel font (10 px characters)
`CHMAP`	9	— (generated)	Minimap (128×128 px, generated from world data)
`CHBUTTON`	10	`button.blp`	Toolbar button icons (35 BUTTON_* types)
`CHGROUND`	11	`floor000–003.blp`	Floor — second channel (for layering)
`CHJAUGE`	12	`jauge.blp`	Energy / progress gauge sprites
`CHTEXT`	13	`text.blp`	Main text font (16×16 px), white, red and slim variants
`CHBIGNUM`	14	`bignum.blp`	Large digit sprites for score / timer

Draw Order (Z-order)

Each game tick renders the scene in this order:

1. Background (CHBACK) — fixed HUD frame
2. Minimap (CHMAP) — 128×128 px top-left
3. Floor tiles (CHFLOOR/CHGROUND) — for each cell in the viewport
4. Objects lower part (CHOBJECT) — overlaid on top of floors
5. Characters — Blupi and enemies (CHBLUPI) with correct Z-order
6. Highlight overlays (CHHILI) — selection boxes, action indicators
7. Objects upper part (CHOBJECTo) — parts of objects that overlap the cell above
8. Fog (CHFOG) — overlays everything in hidden cells
9. HUD elements — gauges (CHJAUGE), buttons (CHBUTTON), text (CHTEXT/CHLITTLE)
10. Mouse cursor (SPRITE_*) — always on top

Coordinate System

The game uses a "diamond" isometric projection:

Grid cell → screen pixel (ConvCelToPos):
  px = (cel.x - celCoin.x) * DIMCELX/2
     - (cel.y - celCoin.y) * DIMCELX/2
     + POSDRAWX + DIMDRAWX/2
  py = (cel.x - celCoin.x) * DIMCELY/2
     + (cel.y - celCoin.y) * DIMCELY/2
     + POSDRAWY

Screen pixel → grid cell (ConvPosToCel): inverse of the above.

ConvPosToCel2(pos): alternative conversion for the editor.

SHIFTBLUPIY=5 shifts Blupi 5 pixels upward for correct Z-order visual effect (the character appears to stand on the surface of the cell).

Highlight Icons (CHHILI, channel 5)

Icon index	Constant	Description
112	`ICON_HILI_STAT`	Statistics highlight
113	`ICON_HILI_SEL`	Character is selected
114	`ICON_HILI_ANY`	General hover
115	`ICON_HILI_OP`	Operation is available
117	`ICON_HILI_GO`	Movement target
118	`ICON_HILI_BUILD`	Build location
119	`ICON_HILI_ERR`	Error (action not possible)

BLP Image Format

Files with .blp extension in image/ are Epsitec's proprietary palette-based bitmap format (BLP = Blupi image Package). Each file contains: - A 256-colour palette - A sequence of named "icons" (frame sprites) - Each icon has its own dimensions and pixel data (8-bit indexed)

Loading is handled by CPixmap::Cache() (via SDL_image in the cross-platform build).