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Use two backgrounds to achieve 30 colors #4

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9a10222
Support 30 colors insteadof 15 by using two backgrounds
pokepress Aug 22, 2025
9ecc14c
Merge pull request #1 from pokepress/multiPaletteSupport
pokepress Aug 22, 2025
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53 changes: 47 additions & 6 deletions generate.py
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Original file line number Diff line number Diff line change
Expand Up @@ -17,7 +17,7 @@

Requires ImageMagick and pdftoppm to convert images, and Docker to compile the
ROM using SGDK. On Ubuntu, install packages "python3", "imagemagick",
"poppler-utils", and "docker.io".
"poppler-utils", "Pillow" and "docker.io".
"""

import argparse
Expand All @@ -28,6 +28,7 @@
import subprocess
import sys
import tempfile
from PIL import Image


# SGDK image to compile the ROM.
Expand All @@ -44,6 +45,10 @@
{image_pointers}
}};

const Image* slides_top[] = {{
{image_pointers_top}
}};

const int num_slides = {num_slides};

#endif // _RES_SLIDES_H_
Expand Down Expand Up @@ -137,6 +142,7 @@ def process_slides(pdf_path, pages_dir, start_page, end_page, app_dir):
# Process those pages by downscaling and reducing colors.
resource_list = []
image_pointers = []
image_pointers_top = []
page_paths = sorted(glob.glob(os.path.join(pages_dir, 'page-*.png')))

page_num = 1
Expand Down Expand Up @@ -173,18 +179,52 @@ def process_slides(pdf_path, pages_dir, start_page, end_page, app_dir):
# Dithering settings.
args.extend(dithering_args)
args.extend([
# Reduce to 15 colors (the max you can do in one palette on Sega).
'-colors', '15',
# Reduce to 30 colors (the max you can do in two palettes on Sega).
'-colors', '30',
# Output a PNG image with an 8-bit palette.
'PNG8:{}'.format(output_path),
])
subprocess.run(check=True, args=args)

#open file and split into backgounds
img = Image.open(output_path)

palette = img.getpalette()
palette_bottom = palette[0:45]
palette_bottom.extend([0] * (768 - len(palette_bottom)))
palette_top = palette_bottom[0:3]
palette_top.extend(palette[45:])
palette_top.extend([0] * (768 - len(palette_top)))

img_bottom = Image.new(mode="P", size=(320,224))
img_bottom.putpalette(palette_bottom)
img_top = Image.new(mode="P", size=(320,224))
img_top.putpalette(palette_top)
img_top.info['transparency'] = 0

for y in range(224):
for x in range(320):
pixel = img.getpixel((x,y))
if pixel < 15:
img_bottom.putpixel((x,y),pixel)
img_top.putpixel((x,y),0)
else:
img_top.putpixel((x,y),pixel-15+1)

img_bottom.save(output_path.replace(".png","_bottom.png"))
img_top.save(output_path.replace(".png","_top.png"))

resource_list.append(
'IMAGE slide_{page_num} {page_filename} BEST'.format(
page_num=page_num, page_filename=page_filename))
'IMAGE slide_{page_num}_bottom {page_filename} BEST'.format(
page_num=page_num, page_filename=page_filename.replace(".png","_bottom.png")))
image_pointers.append(
' &slide_{page_num},'.format(
' &slide_{page_num}_bottom,'.format(
page_num=page_num))
resource_list.append(
'IMAGE slide_{page_num}_top {page_filename_top} BEST'.format(
page_num=page_num, page_filename_top=page_filename.replace(".png","_top.png")))
image_pointers_top.append(
' &slide_{page_num}_top,'.format(
page_num=page_num))

print('\rProcessed {} / {}... '.format(
Expand All @@ -197,6 +237,7 @@ def process_slides(pdf_path, pages_dir, start_page, end_page, app_dir):
with open(os.path.join(app_dir, 'src', 'slides.h'), 'w') as f:
f.write(SLIDES_H_TEMPLATE.format(
image_pointers='\n'.join(image_pointers),
image_pointers_top='\n'.join(image_pointers_top),
num_slides=len(image_pointers)))

with open(os.path.join(app_dir, 'res', 'slide_data.res'), 'w') as f:
Expand Down
10 changes: 8 additions & 2 deletions template/src/main.c
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Original file line number Diff line number Diff line change
Expand Up @@ -15,10 +15,16 @@
static int16_t slide_num;

// Decompress a slide into memory, then flip it to the screen at 0,0 in
// background layer A.
// background layers A & B.
static void displayNewSlide() {
const Image* slide = slides[slide_num];
VDP_drawImage(BG_A, slide, /* x= */ 0, /* y= */ 0);
const Image* slide_top = slides_top[slide_num];
PAL_fadeOutAll(1, false);
VDP_drawImageEx(BG_B, slide, TILE_ATTR_FULL(PAL0, false, false, false, 0),/* x= */ 0, /* y= */ 0, false, false);
int numTile = slide->tileset->numTile;
VDP_drawImageEx(BG_A, slide_top, TILE_ATTR_FULL(PAL1, false, false, false, numTile), /* x= */ 0, /* y= */ 0, false, false);
PAL_fadeToPalette(PAL0,slide->palette->data,1,false);
PAL_fadeToPalette(PAL1,slide_top->palette->data,1,false);
}

// Handle controller events.
Expand Down