VarAction2: Delete provably zero adjustment operations

src/newgrf.cpp

@@ -5626,6 +5626,15 @@ static void NewSpriteGroup(ByteReader *buf)
 				} else {
 					adjust.add_val    = 0;
 					adjust.divmod_val = 0;
+					if (group->adjusts.size() > 1) {
+						/* Not the first adjustment */
+						if (adjust.variable != 0x7E) {
+							if (adjust.and_mask == 0 && IsEvalAdjustWithZeroRemovable(adjust.operation)) {
+								/* Delete useless zero operations */
+								group->adjusts.pop_back();
+							}
+						}
+					}
 				}
 
 				/* Continue reading var adjusts while bit 5 is set. */

src/newgrf_spritegroup.h

@@ -163,6 +163,24 @@ enum DeterministicSpriteGroupAdjustOperation {
 	DSGA_OP_END,
 };
 
+inline bool IsEvalAdjustWithZeroRemovable(DeterministicSpriteGroupAdjustOperation op)
+{
+	switch (op) {
+		case DSGA_OP_ADD:
+		case DSGA_OP_SUB:
+		case DSGA_OP_OR:
+		case DSGA_OP_XOR:
+		case DSGA_OP_ROR:
+		case DSGA_OP_SHL:
+		case DSGA_OP_SHR:
+		case DSGA_OP_SAR:
+			return true;
+
+		default:
+			return false;
+	}
+}
+
 
 struct DeterministicSpriteGroupAdjust {
 	DeterministicSpriteGroupAdjustOperation operation;