VarAction2: Detect and replace scaled reads of train/RV/ship current speed

src/newgrf.cpp

@@ -5929,10 +5929,25 @@ static void NewSpriteGroup(ByteReader *buf)
 									break;
 								case DSGA_OP_SDIV:
 									if ((prev_inference & VA2AIF_SIGNED_NON_NEGATIVE) && adjust.variable == 0x1A && adjust.shift_num == 0 && HasExactlyOneBit(adjust.and_mask)) {
+										uint shift_count = FindFirstBit(adjust.and_mask);
+										if (group->adjusts.size() >= 3 && shift_count == 16 && varsize == 4 && (feature == GSF_TRAINS || feature == GSF_ROADVEHICLES || feature == GSF_SHIPS)) {
+											const DeterministicSpriteGroupAdjust &prev = group->adjusts[group->adjusts.size() - 2];
+											DeterministicSpriteGroupAdjust &prev2 = group->adjusts[group->adjusts.size() - 3];
+											if (prev.operation == DSGA_OP_MUL && prev.type == DSGA_TYPE_NONE && prev.variable == 0x1A && prev.shift_num == 0 && prev.and_mask <= 0xFFFF &&
+													(prev2.operation == DSGA_OP_RST || group->adjusts.size() == 3) && prev2.type == DSGA_TYPE_NONE && prev2.variable == 0xB4 && prev2.shift_num == 0 && prev2.and_mask == 0xFFFF) {
+												/* Replace with scaled current speed */
+												prev2.variable = A2VRI_VEHICLE_CURRENT_SPEED_SCALED;
+												prev2.parameter = prev.and_mask;
+												group->adjusts.pop_back();
+												group->adjusts.pop_back();
+												inference = VA2AIF_SIGNED_NON_NEGATIVE;
+												break;
+											}
+										}
 										/* Convert to a shift */
 										adjust.operation = DSGA_OP_SHR;
-										adjust.and_mask = FindFirstBit(adjust.and_mask);
-										inference |= VA2AIF_SIGNED_NON_NEGATIVE;
+										adjust.and_mask = shift_count;
+										inference = VA2AIF_SIGNED_NON_NEGATIVE;
 									}
 								default:
 									break;

src/newgrf_engine.cpp

@@ -25,6 +25,7 @@
 #include "newgrf_cache_check.h"
 #include "ship.h"
 #include "scope_info.h"
+#include "newgrf_extension.h"
 
 #include "safeguards.h"
 
@@ -477,6 +478,7 @@ static uint32 VehicleGetVariable(Vehicle *v, const VehicleScopeResolver *object,
 
 			case 0x80 + 0x34:
 			case 0x80 + 0x35:
+			case A2VRI_VEHICLE_CURRENT_SPEED_SCALED:
 				if (v->type == VEH_AIRCRAFT) {
 					_sprite_group_resolve_check_veh_check = false;
 				} else {
@@ -878,6 +880,9 @@ static uint32 VehicleGetVariable(Vehicle *v, const VehicleScopeResolver *object,
 
 			return variable == 0xFE ? modflags : GB(modflags, 8, 8);
 		}
+
+		case A2VRI_VEHICLE_CURRENT_SPEED_SCALED:
+			return (v->cur_speed * parameter) >> 16;
 	}
 
 	/*

src/newgrf_extension.h

@@ -60,6 +60,7 @@ enum Action0RemapPropertyIds {
 enum Action2VariableRemapIds {
 	A2VRI_OBJECT_FOUNDATION_SLOPE = 0x100,
 	A2VRI_OBJECT_FOUNDATION_SLOPE_CHANGE,
+	A2VRI_VEHICLE_CURRENT_SPEED_SCALED,
 };
 
 /** Action14 feature definition */

src/newgrf_spritegroup.cpp

@@ -15,6 +15,7 @@
 #include "vehicle_type.h"
 #include "newgrf_cache_check.h"
 #include "string_func.h"
+#include "newgrf_extension.h"
 
 #include "safeguards.h"
 
@@ -634,7 +635,9 @@ void SpriteGroupDumper::DumpSpriteGroup(const SpriteGroup *sg, int padding, uint
 					continue;
 				}
 				p += seprintf(p, lastof(this->buffer), "%*svar: %X", padding, "", adjust.variable);
-				if (adjust.variable >= 0x100) {
+				if (adjust.variable == A2VRI_VEHICLE_CURRENT_SPEED_SCALED) {
+					p += seprintf(p, lastof(this->buffer), " (current_speed_scaled)");
+				} else if (adjust.variable >= 0x100) {
 					extern const GRFVariableMapDefinition _grf_action2_remappable_variables[];
 					for (const GRFVariableMapDefinition *info = _grf_action2_remappable_variables; info->name != nullptr; info++) {
 						if (adjust.variable == info->id) {