Add project logo and use it for the app icon

- assets/logo.png (transparent) and assets/logo-256.png for the site
  and README
- tools/make_icon.m builds the full-bleed iOS icon from the logo

README.md

@@ -1,4 +1,6 @@
-# Factorio on iPhone
+<p align="center"><img src="assets/logo-256.png" width="160" alt="Factorio for iPhone logo"></p>
+
+<h1 align="center">Factorio on iPhone</h1>
 
 Play your own copy of **Factorio** on your iPhone. You build the app on your Mac from the
 Factorio you already own on Steam, and install it on your phone with a cable.
@@ -130,6 +132,9 @@ git pull
 - [docs/research/](docs/research/static-translation.md): earlier research (ARM64 → WASM
   translation).
 
+**Logo:** `assets/logo.png` (transparent, 683 px) and `assets/logo-256.png` are the project's own
+artwork, also used for the app icon. They are not Factorio's official logo.
+
 **Third-party software:** [Wuffs](https://github.com/google/wuffs) (Apache-2.0) is downloaded
 during the build to decode PNG images. Factorio itself uses [SDL](https://github.com/libsdl-org/SDL)
 (zlib). Factorio is a trademark of Wube Software Ltd.; all game code and assets belong to them.

docs/building.md

@@ -66,7 +66,7 @@ only.
 2. **Retarget.** `tools/retarget.py` writes `build/native/Factorio.dylib`, changing only Mach-O
    header bytes, and records the changes in `build/native/retarget.json`.
 3. **Shims and host.** The shim libraries and the small host executable are compiled for iOS
-   with clang; the app icon is generated from the game's own icon.
+   with clang; the app icon is generated from `assets/logo.png`.
 4. **Bundle and sign.** `build/native/Factorio.app` is assembled, signed, and installed with
    `devicectl`.
 5. **Data.** `--push-data` copies the game's `data/` folder (~1.5 GB) into the app's

tools/build_native.py

@@ -96,14 +96,14 @@ def dylib(name, sources, defines=(), reexport=None, link_appkit=True, extra=()):
 
 
 def build_icon():
-    """Compile an asset catalog with the app icon, made from the game's own icon; returns plist keys."""
+    """Compile an asset catalog with the app icon, made from assets/logo.png; returns plist keys."""
     work = OUT / "icon"
     iconset = work / "Assets.xcassets/AppIcon.appiconset"
     iconset.mkdir(parents=True, exist_ok=True)
     tool = work / "make_icon"
     run(["xcrun", "clang", "-O2", "-fobjc-arc", ROOT / "tools/make_icon.m", "-framework", "Foundation",
          "-framework", "CoreGraphics", "-framework", "ImageIO", "-o", tool])
-    run([tool, GAME / "data/core/graphics/factorio-icon@2x.png", iconset / "AppIcon-1024.png"])
+    run([tool, ROOT / "assets/logo.png", iconset / "AppIcon-1024.png"])
     (iconset / "Contents.json").write_text(json.dumps({"images": [{"filename": "AppIcon-1024.png", "idiom": "universal",
         "platform": "ios", "size": "1024x1024"}], "info": {"author": "xcode", "version": 1}}))
     (work / "Assets.xcassets/Contents.json").write_text(json.dumps({"info": {"author": "xcode", "version": 1}}))

tools/make_icon.m

@@ -1,6 +1,6 @@
-// Builds the 1024x1024 iOS app icon from the game's own 128 px icon (read from the local install).
+// Builds the 1024x1024 iOS app icon from the project logo (assets/logo.png, transparent).
-// The gear is scaled with high-quality interpolation onto an opaque dark background
+// The emblem is drawn with high-quality interpolation onto an opaque, full-bleed dark background:
-// (iOS app icons must be opaque).
+// iOS app icons must be opaque and square (the system applies the rounded mask).
 // Usage: make_icon SOURCE_PNG OUTPUT_PNG
 #import <Foundation/Foundation.h>
 #import <CoreGraphics/CoreGraphics.h>
@@ -21,7 +21,7 @@ int main(int argc, char **argv) {
         CGContextDrawRadialGradient(ctx, gradient, CGPointMake(size / 2.0, size * 0.55), 0,
                                     CGPointMake(size / 2.0, size / 2.0), size * 0.75, kCGGradientDrawsAfterEndLocation);
         CGContextSetInterpolationQuality(ctx, kCGInterpolationHigh);
-        CGFloat inset = size * 0.12;
+        CGFloat inset = size * 0.14;  // keep the emblem clear of the mask's corners
         CGContextDrawImage(ctx, CGRectMake(inset, inset, size - 2 * inset, size - 2 * inset), gear);
         CGImageRef icon = CGBitmapContextCreateImage(ctx);
         CGImageDestinationRef dst = CGImageDestinationCreateWithURL((__bridge CFURLRef)[NSURL fileURLWithPath:@(argv[2])],