fix #17 - add defaultSpeedLimit setting

src/main/java/net/pcal/highspeed/HighspeedConfig.java

@@ -7,13 +7,13 @@ public record HighspeedConfig(
         List<HighspeedBlockConfig> blockConfigs,
         boolean isSpeedometerEnabled,
         boolean isTrueSpeedometerEnabled,
-        boolean isIceBoatsEnabled
+        boolean isIceBoatsEnabled,
+        Integer defaultSpeedLimit
 ) {
 
     public record HighspeedBlockConfig(
             ResourceLocation blockId,
-            int cartSpeed
+            Integer speedLimit
     ) {
     }
 }
-

src/main/java/net/pcal/highspeed/HighspeedConfigParser.java

@@ -25,7 +25,7 @@ static HighspeedConfig parse(final InputStream in) throws IOException {
         for (HighspeedBlockConfigGson blockGson : configGson.blocks) {
             HighspeedBlockConfig bc = new HighspeedBlockConfig(
                     ResourceLocation.parse(requireNonNull(blockGson.blockId, "blockId is required")),
-                    requireNonNull(blockGson.cartSpeed)
+                    blockGson.cartSpeed != null ? blockGson.cartSpeed : blockGson.speedLimit
             );
             blocks.add(bc);
         }
@@ -34,7 +34,8 @@ static HighspeedConfig parse(final InputStream in) throws IOException {
                 Collections.unmodifiableList(blocks),
                 requireNonNull(configGson.isSpeedometerEnabled, "isSpeedometerEnabled must be set"),
                 requireNonNull(configGson.isTrueSpeedometerEnabled, "isTrueSpeedometerEnabled must be set"),
-                requireNonNull(configGson.isIceBoatsEnabled, "isIceBoatsEnabled must be set")
+                requireNonNull(configGson.isIceBoatsEnabled, "isIceBoatsEnabled must be set"),
+                configGson.defaultSpeedLimit // may be null
         );
     }
 
@@ -59,10 +60,12 @@ public static class HighspeedConfigGson {
         Boolean isSpeedometerEnabled;
         Boolean isTrueSpeedometerEnabled;
         Boolean isIceBoatsEnabled;
+        Integer defaultSpeedLimit;
     }
 
     public static class HighspeedBlockConfigGson {
         String blockId;
-        Integer cartSpeed;
+        Integer speedLimit;
+        Integer cartSpeed; // for backward compat
     }
 }

src/main/java/net/pcal/highspeed/HighspeedService.java

@@ -1,13 +1,16 @@
 package net.pcal.highspeed;
 
+import com.google.common.collect.ImmutableMap;
 import net.fabricmc.api.ModInitializer;
 import net.minecraft.resources.ResourceLocation;
+
 import java.io.FileInputStream;
 import java.io.IOException;
 import java.io.InputStream;
 import java.nio.file.Path;
 import java.nio.file.Paths;
 import java.nio.file.StandardCopyOption;
+import java.util.Map;
 
 import static java.util.Objects.requireNonNull;
 
@@ -19,6 +22,7 @@ public class HighspeedService implements ModInitializer {
     private static HighspeedService INSTANCE = null;
     private HighspeedConfig config;
     private HighspeedClientService clientService;
+    private Map<ResourceLocation, Integer> speedLimitPerBlock;
 
     public static HighspeedService getInstance() {
         return requireNonNull(INSTANCE);
@@ -50,6 +54,11 @@ public void onInitialize() {
         } catch (IOException e) {
             throw new RuntimeException(e);
         }
+
+        final ImmutableMap.Builder<ResourceLocation, Integer> b = ImmutableMap.builder();
+        this.config.blockConfigs().forEach(bc->b.put(bc.blockId(), bc.speedLimit()));
+        this.speedLimitPerBlock = b.build();
+
         if (INSTANCE != null) throw new IllegalStateException();
         INSTANCE = this;
     }
@@ -62,11 +71,12 @@ public void initClientService(HighspeedClientService clientService) {
     // ===================================================================================
     // Public methods
 
-    public Integer getCartSpeed(ResourceLocation id) {
-        for (HighspeedConfig.HighspeedBlockConfig bc : this.config.blockConfigs()) {
-            if (id.equals(bc.blockId())) return bc.cartSpeed();
-        }
-        return null;
+    /**
+     * @return the maximum speed (in blocks-per-second) that a cart travelling on a rail sitting
+     * on the given block type can travel at.  Returns null if the vanilla default should be used.
+     */
+    public Integer getSpeedLimit(ResourceLocation blockId) {
+        return this.speedLimitPerBlock.getOrDefault(blockId, this.config.defaultSpeedLimit());
     }
 
     public boolean isSpeedometerEnabled() {
@@ -85,5 +95,4 @@ public HighspeedClientService getClientService() {
         if (this.clientService == null) throw new UnsupportedOperationException("clientService not initialized");
         return this.clientService;
     }
-
 }

src/main/java/net/pcal/highspeed/mixins/AbstractMinecartEntityMixin.java

@@ -25,7 +25,7 @@ public abstract class AbstractMinecartEntityMixin {
     private static final double SQRT_TWO = 1.414213;
 
     private BlockPos lastPos = null;
-    private double maxSpeed = VANILLA_MAX_SPEED;
+    private double currentMaxSpeed = VANILLA_MAX_SPEED;
     private double lastMaxSpeed = VANILLA_MAX_SPEED;
     private Vec3 lastSpeedPos = null;
     private long lastSpeedTime = 0;
@@ -54,7 +54,7 @@ protected void getMaxSpeed(CallbackInfoReturnable<Double> cir) {
 
     private double getModifiedMaxSpeed() {
         final BlockPos currentPos = minecart.blockPosition();
-        if (currentPos.equals(lastPos)) return maxSpeed;
+        if (currentPos.equals(lastPos)) return currentMaxSpeed;
         lastPos = currentPos;
         // look at the *next* block the cart is going to hit
         final Vec3 v = minecart.getDeltaMovement();
@@ -67,19 +67,19 @@ private double getModifiedMaxSpeed() {
         if (nextState.getBlock() instanceof BaseRailBlock rail) {
             final RailShape shape = nextState.getValue(rail.getShapeProperty());
             if (shape == RailShape.NORTH_EAST || shape == RailShape.NORTH_WEST || shape == RailShape.SOUTH_EAST || shape == RailShape.SOUTH_WEST) {
-                return maxSpeed = VANILLA_MAX_SPEED;
+                return currentMaxSpeed = VANILLA_MAX_SPEED;
             } else {
                 final BlockState underState = minecart.level().getBlockState(currentPos.below());
                 final ResourceLocation underBlockId = BuiltInRegistries.BLOCK.getKey(underState.getBlock());
-                final Integer cartSpeedBps = HighspeedService.getInstance().getCartSpeed(underBlockId);
-                if (cartSpeedBps != null) {
-                    return maxSpeed = cartSpeedBps / 20.0;
+                final Integer speedLimit = HighspeedService.getInstance().getSpeedLimit(underBlockId);
+                if (speedLimit != null) {
+                    return currentMaxSpeed = speedLimit / 20.0;
                 } else {
-                    return maxSpeed = VANILLA_MAX_SPEED;
+                    return currentMaxSpeed = VANILLA_MAX_SPEED;
                 }
             }
         } else {
-            return maxSpeed = VANILLA_MAX_SPEED;
+            return currentMaxSpeed = VANILLA_MAX_SPEED;
         }
     }
 
@@ -90,7 +90,7 @@ private void clampVelocity() {
             minecart.setDeltaMovement(new Vec3(Mth.clamp(vel.x, -smaller, smaller), 0.0,
                     Mth.clamp(vel.z, -smaller, smaller)));
         }
-        lastMaxSpeed = maxSpeed;
+        lastMaxSpeed = currentMaxSpeed;
     }
 
     private void updateSpeedometer() {

src/main/resources/net/pcal/highspeed/default-config.json5

@@ -1,31 +1,40 @@
 // NOTE: This is not actually json5 - it's parsed with minecraft's built-in json parser but with
-// some preprocessing to allow for '//' -style comments like this one.  The lie in the .json5 
+// some preprocessing to allow for '//' -style comments like this one.  The lie in the .json5
 // extension just helps text editors deal with it.
 {
 
-
-  //
-  // List of blocks and how they affect a train travelling on top.  cartSpeed is in blocks-per-second.
-  //
+  // Sets the maximum speed (in blocks-per-second) for carts travelling on specific blocks.  The speedLimit in
+  // Vanilla is 8.
   'blocks' : [
     {
-        'blockId': 'minecraft:gravel',
-        'cartSpeed': 40
+      'blockId': 'minecraft:gravel',
+      'speedLimit': 40
+    },
+    {
+      'blockId': 'minecraft:slime_block',
+      'speedLimit': 4
     }
   ],
 
-  // Whether a speedometer should be displayed when you get in a minecart.
+  // Sets the default maximum speed for blocks not configured above.  A value of 'null' here means to use the
+  // Vanilla speedLimit (8).
   //
-  // The mod must be installed on the client for this to work.
+  // If you change this, you should also configure at least one kind of block to maintain Vanilla speed (i.e.,
+  // by setting 'speedLimit' for a block to be 8 (or null) in the 'blocks' section above).  Experience shows that
+  // carts can derail or reverse unexpectedly in certain situations when travelling above the Vanilla speed limit,
+  // so you'll want to have at least one block type that can act as a 'brake.'
+  'defaultSpeedLimit'        : null,
+
+  // Whether a speedometer should be displayed when you get in a minecart.  The mod must be installed on the client
+  // in order for this to work.
   'isSpeedometerEnabled'     : true,
 
-  // Whether the 'true' speed should also be displayed on the speedometer.  The deafult speedometer just shows your
+  // Whether the 'true' speed should also be displayed on the speedometer.  The default speedometer just shows your
   // approximate speed; this precisely measures distance travelled every tick.  It's more resource-intensive
   // and also flickers sort of annoyingly, so disabled by default.  There's usually not much difference, anyway.
   'isTrueSpeedometerEnabled' : false,
 
   // Whether Vanilla ice boats should be allowed.  Set to 'false' to limit ice boats to ground speed; 'true'
-  //
   // The mod must be installed on the client for this to work.
   'isIceBoatsEnabled'        : false
 }