Palette Workflow

Mode 13h gives you one 256-color palette for the whole screen. If your game shows a full-screen picture and a HUD, both have to share it — so you split the palette into a fixed range and a swappable range.

This page covers the whole pipeline: reserving the ranges, authoring the art in Pix8, and swapping palettes at runtime. For the API itself see VGA.

Splitting the palette

Decide the split once, then keep it for the life of the project. A typical layout for a game with full-screen artwork:

Range	Count	Contents	Changes
`0`–`31`	32	HUD, fonts, sprites, UI widgets	Never
`32`–`255`	224	The current full-screen image	Per picture/level

Color 0 stays transparent by engine convention, so keep it in the fixed range.

The proportions are yours to pick — the reverse split (224 for game graphics, 32 for UI at the top) works equally well. What matters is that one range never moves, so your HUD colors stay stable while backgrounds come and go.

Authoring in Pix8

1. The fixed UI palette

Build your 32 UI colors once and save them on their own:

Open the palette editor
Enable 6-bit mode — the VGA DAC is 6 bits per channel, so this shows you the colors the hardware will actually produce
Set up entries 0–31
Save the palette as 6-bit raw binary to UI.PAL

The engine’s LoadPalette reads a raw 768-byte file of 0–63 values. Choose 6-bit raw, not 8-bit JASC-PAL — the text format will not load.

2. Each full-screen image

Quantize to the size of your swappable range, then move the block into position:

File → Open the source image (PNG/JPG/WebP)
In the import dialog set Colors to 224 and pick a dither mode (Floyd–Steinberg for photographic art, None for flat illustration)
The quantized colors land at indices 0–223. Open the palette editor, select the range 0–223, and X-Swap it onto index 32.
Paste or re-enter your 32 UI colors into 0–31 — or load UI.PAL
File → Export as… → PCX

Use X-Swap, not Swap. Swap moves the colors only; the pixels still point at the old indices and the image scrambles. X-Swap remaps the pixel data along with the colors, so the picture looks identical while the indices move underneath. The same distinction applies to every reordering operation in the palette editor.

Loading at runtime

Apply the fixed range once at startup, then only ever upload the swappable range:

uses VGA, PCX;

var
  UIPal: TPalette;
  StagePal: TPalette;
  StageImage: TImage;

begin
  { Once at startup - the HUD colors }
  LoadPalette('DATA\UI.PAL', UIPal);
  SetPartialPalette(UIPal, 0, 31);

  { Per picture - only touches 32-255, the HUD is unaffected }
  LoadPCXWithPalette('DATA\STAGE1.PCX', StageImage, StagePal);
  SetPartialPalette(StagePal, 32, 255);

SetPartialPalette indexes the source array at FromColor, so entries 32–255 of StagePal go to DAC registers 32–255. Whatever the stage PCX happens to hold in 0–31 is never uploaded, which means a stage file cannot corrupt your HUD colors.

That is the reason to keep UI.PAL separate rather than relying on every stage PCX carrying identical UI entries: with the separate file, nothing needs to stay in sync across your image set.

Swapping to the next picture is then just:

LoadPCXWithPalette('DATA\STAGE2.PCX', StageImage, StagePal);
SetPartialPalette(StagePal, 32, 255);

Avoiding the flash

Uploading a palette while the new image is only half-drawn shows a frame of wrong colors. Two ways around it:

Draw first, then swap — render the image into a framebuffer, WaitForVSync, then call SetPartialPalette
Fade through black — ramp the swappable range down to black, load the new image and palette, then ramp back up. Because you are only touching 32–255, the HUD stays lit the whole time

Palette effects

RotatePalette(StartColor, Count, Direction) cycles a sub-range in the DAC directly, which is how you get running water, fire or marquee lights for free. Confine it to a handful of indices inside your swappable range, and it costs nothing per frame:

RotatePalette(240, 16, 1);  { Cycle colors 240-255 to the right }

It writes the hardware palette directly — no SetPalette call afterwards.