GTA 1 Map Editor
Posted: 15 May 2026, 22:31
Just released my first early version of map editor for GTA1 was a fan of Junction 25 but wanted something open source. BTW, do plan to open source later my web clone of GTA just need to ship without original gta assets.
https://github.com/VBGAMER45/gta1-mapeditor
A Windows desktop editor for Grand Theft Auto 1 .CMP map files (with .G24 style data). Spiritual successor to the original Junction25 editor, written in C# / .NET 8 with WinForms + OpenTK.
Reads stock maps directly from the original game (NYC.CMP, SANB.CMP, MIAMI.CMP), renders them with the same tile graphics the game itself uses, and lets you edit blocks, objects, vehicles, and spawn locations with full undo/redo.
By vbgamer45
Screenshots
2D top-down — pure orthographic view, what Junction25 shows. Tile graphics decoded straight from .G24; placed cars and objects render with their actual G24 sprites at correct rotation.
Top-down view of NYC.CMP
2.5D isometric — dimetric projection, full lid + wall mesh with depth-buffered occlusion. Same atlas, slope-aware lids.
Isometric view of NYC.CMP
3D free-look — perspective camera, WASD + right-drag mouse-look. Scrollbars pan horizontally; Q/E adjust elevation.
3D free-look view of NYC.CMP
Status
Functional. Decoded G24 tile output is byte-identical to the engine's own reference (verified by an automated diff against pre-extracted reference PNGs in the companion web port — full coverage in tests/GTA1MapEditor.Tests/TileDecodeVsPngTests.cs).
What works
Map I/O
Read & round-trip-write GTA1 .CMP files (full header, base, columns, blocks, objects, car positions, routes, nav sectors, spawn locations).
Read .G24 style files (tiles, animation, paged CLUTs, palette indices, object info, car info, sprite info & graphics, sprite numbers).
Views (toggle via toolbar / Ctrl+1/2/3)
2D top-down — every block's lid in stack order, so transparent overlays composite correctly. Pan, wheel-zoom, scrollbars, Fit/100% native (Ctrl+9).
2.5D isometric — dimetric projection, full lid + wall mesh, depth-buffered.
3D free-look — WASD + right-drag mouse-look + Q/E elevation.
Editing
Block attributes panel (Junction25-style): per-tile cube type, slope, rotation, walls, lid, traffic flags, railway flags, brightness remap, z-stack navigator.
Section-aware tile picker (Side / Lid / Aux) with sprite previews.
Place / move / delete objects, cars, and spawn locations (Police / Hospital / Fire). Drag entities by clicking and dragging in Select mode; right-click for properties dialog.
Tile paint tool with eyedropper (right-click).
Sprite-based entity rendering in 2D top-down — placed cars and objects show their actual G24 sprites with correct rotation, not placeholder markers.
Clone-on-write per-tile editing keeps shared block records intact.
Full undo / redo (Ctrl+Z / Ctrl+Y).
Quality of life
File → Open Recent (last 5 maps).
Edit → Go to Tile (Ctrl+G).
Side panel listing every Object / Car / Route / Sector / Spawn with Go-to + Delete.
Traffic-direction arrow overlay (F2).
Automatic G24 lookup: opens a .CMP, finds the matching styleNNN.g24 in sibling folders.
Optional pre-extracted PNG tiles fallback (used automatically when tiles/{side,lid,auxiliary}/*.png are present beside the style).
https://github.com/VBGAMER45/gta1-mapeditor
A Windows desktop editor for Grand Theft Auto 1 .CMP map files (with .G24 style data). Spiritual successor to the original Junction25 editor, written in C# / .NET 8 with WinForms + OpenTK.
Reads stock maps directly from the original game (NYC.CMP, SANB.CMP, MIAMI.CMP), renders them with the same tile graphics the game itself uses, and lets you edit blocks, objects, vehicles, and spawn locations with full undo/redo.
By vbgamer45
Screenshots
2D top-down — pure orthographic view, what Junction25 shows. Tile graphics decoded straight from .G24; placed cars and objects render with their actual G24 sprites at correct rotation.
Top-down view of NYC.CMP
2.5D isometric — dimetric projection, full lid + wall mesh with depth-buffered occlusion. Same atlas, slope-aware lids.
Isometric view of NYC.CMP
3D free-look — perspective camera, WASD + right-drag mouse-look. Scrollbars pan horizontally; Q/E adjust elevation.
3D free-look view of NYC.CMP
Status
Functional. Decoded G24 tile output is byte-identical to the engine's own reference (verified by an automated diff against pre-extracted reference PNGs in the companion web port — full coverage in tests/GTA1MapEditor.Tests/TileDecodeVsPngTests.cs).
What works
Map I/O
Read & round-trip-write GTA1 .CMP files (full header, base, columns, blocks, objects, car positions, routes, nav sectors, spawn locations).
Read .G24 style files (tiles, animation, paged CLUTs, palette indices, object info, car info, sprite info & graphics, sprite numbers).
Views (toggle via toolbar / Ctrl+1/2/3)
2D top-down — every block's lid in stack order, so transparent overlays composite correctly. Pan, wheel-zoom, scrollbars, Fit/100% native (Ctrl+9).
2.5D isometric — dimetric projection, full lid + wall mesh, depth-buffered.
3D free-look — WASD + right-drag mouse-look + Q/E elevation.
Editing
Block attributes panel (Junction25-style): per-tile cube type, slope, rotation, walls, lid, traffic flags, railway flags, brightness remap, z-stack navigator.
Section-aware tile picker (Side / Lid / Aux) with sprite previews.
Place / move / delete objects, cars, and spawn locations (Police / Hospital / Fire). Drag entities by clicking and dragging in Select mode; right-click for properties dialog.
Tile paint tool with eyedropper (right-click).
Sprite-based entity rendering in 2D top-down — placed cars and objects show their actual G24 sprites with correct rotation, not placeholder markers.
Clone-on-write per-tile editing keeps shared block records intact.
Full undo / redo (Ctrl+Z / Ctrl+Y).
Quality of life
File → Open Recent (last 5 maps).
Edit → Go to Tile (Ctrl+G).
Side panel listing every Object / Car / Route / Sector / Spawn with Go-to + Delete.
Traffic-direction arrow overlay (F2).
Automatic G24 lookup: opens a .CMP, finds the matching styleNNN.g24 in sibling folders.
Optional pre-extracted PNG tiles fallback (used automatically when tiles/{side,lid,auxiliary}/*.png are present beside the style).