Getting Started

Getting Started

An example project setup using Super Mario World (USA).sfc.

This tutorial edits the Mountains background in Super Mario World (Super Mario World (USA).sfc). This is the background with tall spotted hills in the intro level and in Yoshi's House.

You will set up:

• a palette
• four tile sheets
• a stamp table
• a map

All addresses are hex file offsets. The ROM has no header, so SNES address $0C:D900 is file offset $65900.

Use a copy of the ROM. celPix writes to the file in place. It does not make a backup.

1. Open the ROM and save a project

1. File ▸ Open pixel data…, then open the ROM.
2. File ▸ Save Project As… (Ctrl+Shift+S). Save it as smw.celpix in the same folder as the ROM.

A project stores offsets and settings. It does not store a copy of the ROM data.

2. Find the graphics

The tile sheets are 3bpp and compressed. They are stored one after another.

1. In Offset under the canvas, type $459F9 and press Enter.
2. Set Pixel to SNES 3bpp, loaded as 4bpp (8x8). The game expands these sheets to 4bpp when it loads them, so their palette rows are 16 colours.

3. Set Compression to LZ2 improved (SMW, Yoshi's Island). The Decompressed view window shows the unpacked sheet.

The status line shows the packed size, for example structure 0x838 B.

4. Click Jump to Next to go to the next sheet. The sheets start at $459F9, $46231, $46CBB, and so on.

LZ2 improved unpacks the same data as LZ2. It packs about 10% smaller. There is no free space between the sheets, so an edited sheet must not pack larger than the original.

Scan stops at any data that LZ2 can unpack. Smart Scan also checks that the result looks like graphics.

5. Go to $54C66. This sheet has the hill graphics.

3. Take a palette from a save state

The game builds its palette while it runs. The ROM has no palette to read, so take it from an emulator save state (Mesen or Snes9x).

1. In the emulator, start a new game. Make a save state in the first level after the file select screen (the intro level).
2. In the Palette dock, change Default to Emulator State.
3. Select the save state file.

The hills use palette row 0. Row 0 is selected by default.

4. Carve the sheets as slices

A slice is a region of the file that is saved as its own entry.

1. File ▸ New Slice from View. The offset, compression and length are filled in.
2. Name the slice GFX1B and click OK.

Make the other three slices:

1. Select the ROM in Files.
2. File ▸ New Slice….
3. Enter the name and offset from the table.
4. Set Compression to LZ2 improved. Leave Length blank.

Name	Offset
GFX14	$51348
GFX17	$529B4
GFX15	$51AE8

5. Edit pixels

1. Open GFX1B.
2. Set Zoom to 6.
3. Click Pixel Mode (E).
4. Select a tool: Select, Pencil, Eyedropper, Fill, Line, Rectangle, Filled Rectangle, Ellipse or Filled Ellipse (keys 1 to 9).
5. Select a colour in the Palette dock and draw.

A ● next to an entry means it has unsaved changes. Edit ▸ Undo (Ctrl+Z) undoes one stroke.

6. Assemble the tile window

The background uses tile numbers $000 to $1FF. These numbers point into the area of video memory (VRAM) that the four sheets are loaded into. A composite puts entries one after another to make that area.

1. File ▸ New Composite View….
2. In Add source…, pick the sheets in this order: GFX14, GFX17, GFX1B, GFX15.
3. Name the composite Level tiles and click OK.

4. Set the palette to the save state again.
5. Set Rows to 32.

To see where each sheet is placed: right-click ▸ Edit….

7. Carve the stamp table

The background is made of 16×16 stamps. Each stamp is four tilemap words. Each word gives a tile number, a palette row and flip settings. The game calls these Map16 blocks. The table has 256 stamps.

1. Select the ROM in Files.
2. File ▸ New Slice…, with these values:

Content	Tilemap
Name	Background stamps
Offset	$69100
Length	$800
Compression	None (uncompressed)

3. Set Tilemap to SNES stamp table (2x2 words, down each column).
4. Under the canvas, set Tiles to Level tiles.

The four words of each stamp are stored in this order: upper-left, lower-left, upper-right, lower-right. Because of this, the table looks like strips when you view it directly. The map in the next step draws each stamp correctly.

8. Carve the map

The map has one byte per stamp. It is compressed with RLE1 at $65900. RLE1 data has an end marker, so leave Length blank.

1. Select the ROM in Files.
2. File ▸ New Slice…, with these values:

Content	Tilemap
Name	Mountains
Offset	$65900
Compression	RLE1 (SMW, $FF $FF terminated)

3. Set Tilemap to Metatile index map (byte -> 2x2 record of a packed table).
4. Set Cols to 32.

5. Set Tiles to Background stamps.

The map has two screens. Each screen is 16×27 stamps. The second screen shows below the first.

The cross you drew in step 5 shows on each hill edge that uses that tile.

9. Edit the map

1. Click Edit Tiles (T).
2. Open the Tile Source tab. It shows the stamps in the table.
   • Left-click selects one stamp.
   • Right-drag selects a range of stamps.
3. Click the map to place the selected stamps.

For example, right-drag from the middle of the cloud to its right end. Then click the map two times at the right end of the first cloud. The cloud is now longer.

Right-click the map to pick up the stamp under the pointer.

10. Write the ROM

1. File ▸ Write All (Ctrl+Shift+W).
2. File ▸ Save Project (Ctrl+S).

Each compressed entry must fit in its original space after it is packed again. The longer cloud fits.

A new cloud in the empty sky does not fit. The sky is one long run of empty stamps. A cloud in the middle of the run makes the packed data larger. celPix refuses the write:

To fix this, undo the change, or remove data somewhere else in the map. Test the ROM in an emulator.

The feature tutorials on Home start from this project.