[all] Trendlines forward/backward fixes

common/Charts/ChartsDrawer.js

@@ -1992,11 +1992,20 @@ CChartsDrawer.prototype =
 				}
 			} else {
 				if(series.length > 0) {
-					//возможно стоит пройтись по всем сериям
-					seria = series[0];
-					numCache = t.getNumCache(seria.val);
+					// every chart except scatter should start from 1
 					min = 1;
-					max = numCache ? numCache.ptCount : 1;
+					max = 1;
+					// find max value across each seria
+					for (let i = 0; i < series.length; i++) {
+						const seria = series[i];
+						if (seria) {
+							numCache = t.getNumCache(seria.val);
+							const ptCount = numCache && AscFormat.isRealNumber(numCache.ptCount) ? numCache.ptCount : 0;
+							// trendline can affect max value
+							const newMax = seria.trendline && seria.trendline.forward && ptCount > 1 ? ptCount + seria.trendline.forward : ptCount;
+							max = Math.max(max, newMax);
+						}
+					}
 				}
 			}
 		};
@@ -2019,6 +2028,12 @@ CChartsDrawer.prototype =
 						newArr[l][j] = [val.x, val.y];
 					}
 				}
+
+				// check the impact of trendline on scatter chart
+				if (series[l].trendline) {
+					min = series[l].trendline.backward ? min - series[l].trendline.backward : min;
+					max = series[l].trendline.forward ? max + series[l].trendline.forward : max;
+				}
 			}
 		};
 
@@ -17588,8 +17603,8 @@ CColorObj.prototype =
 				const coefficients = this._getEquationCoefficients(coords.catVals, coords.valVals, type, order, attributes.intercept);
 				const equationStorage = this._obtainEquationStorage(type);
 				if (coefficients && equationStorage) {
-					let catMax = catAxis.max + attributes.forward;
-					let catMin = catAxis.min + attributes.backward;
+					let catMax = catAxis.max;
+					let catMin = catAxis.min;
 					const midPointsNum = 100;
 					const lineBuilder = new CLineBuilder(coefficients, catMin, catMax, valAxis.scaling.min, valAxis.scaling.max, valAxis.scaling.logBase);
 					lineBuilder.setCalcYVal(equationStorage.calcYVal);

common/Drawings/Format/ChartSpace.js

@@ -4783,7 +4783,9 @@ function(window, undefined) {
 								oCurPts = oSeries.val.numLit;
 							}
 							if (oCurPts) {
-								nPtsLength = Math.max(nPtsLength, oCurPts.ptCount);
+								const forward = oSeries.trendline && oSeries.trendline.forward ? oSeries.trendline.forward : 0;
+								const newNPtsLength = oCurPts.ptCount + forward;
+								nPtsLength = Math.max(nPtsLength, newNPtsLength);
 							}
 						}
 					}