| name | palette |
| description | Design BGR555 color palettes for the SNES menu ROM. Use when discussing colors, gradients, themes, or editing palette.a65 or HDMA gradient tables in const.a65. |
| argument-hint | [color-spec or theme-name] |
SNES Palette Design Tool
Help design BGR555 color palettes for the sd2snes menu ROM.
BGR555 Conversion
Each color: 2 bytes little-endian. Bit layout: 0bbbbbgg_gggrrrrr (15-bit)
RGB to BGR555:
- Scale 0-255 to 0-31:
ch5 = round(ch8 / 255 * 31)
- Pack:
bgr555 = (blue5 << 10) | (green5 << 5) | red5
- Split:
low = bgr555 & 0xFF, high = (bgr555 >> 8) & 0xFF
- Output:
.byt $XX, $YY (low first)
Quick reference:
| RGB Hex | BGR555 bytes | R,G,B (5-bit) |
|---|
| #000000 | $00, $00 | 0, 0, 0 |
| #FFFFFF | $FF, $7F | 31, 31, 31 |
| #FF0000 | $1F, $00 | 31, 0, 0 |
| #00FF00 | $E0, $03 | 0, 31, 0 |
| #0000FF | $00, $7C | 0, 0, 31 |
| #FF00FF | $1F, $7C | 31, 0, 31 |
| #FFFF00 | $FF, $03 | 31, 31, 0 |
| #00FFFF | $E0, $7F | 0, 31, 31 |
Palette File: snes/palette.a65
512 bytes = 256 colors, 2 bytes each in BGR555.
- Color 0 palette 0 = background (overridden by HDMA gradient)
- Palette 0 = normal text colors
- Palette 1 = bold/highlight text (print_pal = 1)
- Palettes 2-7 = logo and sprite palettes
HDMA Gradient: snes/const.a65 label hdma_pal_src
Format: scanline_count, low_byte, high_byte repeated, $00 terminator.
HDMA channels 1+2 change background color 0 per scanline group:
- Channel 1 writes 0 to CGADD (targets color 0)
- Channel 2 writes BGR555 to CGDATA
Current gradient regions:
- Lines 1-44: Logo area (bright pink)
- Lines 45-54: Black transition
- Lines 55-67: Accent
- Lines 68-178: Graduated dark-to-bright ramp (text area)
- Lines 179+: Bottom border
Designing a new gradient:
- Choose a base hue
- Create 10-12 steps from dark to bright
- Logo area (first ~44 lines) = brightest
- Ramp dark-to-bright over text area (~110 lines)
- Bottom border accents
Selection Bar: snes/const.a65 labels hdma_math_src and hdma_bar_color_src
hdma_bar_color_src has two 4-byte entries (normal + highlight):
.byt $RR, $GG, $BB, $GG2 ; normal COLDATA values
.byt $RR, $GG, $BB, $GG2 ; highlight COLDATA values
COLDATA format ($2132): [bit7=B][bit6=G][bit5=R][bits4-0=intensity]
$3f = R=31, $5f = G=31, $9f = B=31$20 = R=0, $40 = G=0, $80 = B=0
Workflow
When the user requests a new color scheme:
- Convert requested colors to BGR555
- Generate palette.a65 entries (if modifying text/logo colors)
- Generate hdma_pal_src gradient table
- Generate matching hdma_bar_color_src entries
- Show values with comments
- After editing, suggest
/build then /test to preview
