scroll horizontally when dragging a selection

bigtext.py

@@ -79,8 +79,6 @@ class InnerBigText(QWidget):
             self.selection_highlight,
         ]
 
-    def paintEvent(self, event: QPaintEvent) -> None:
-        self.draw()
 
     def keyPressEvent(self, e: QKeyEvent) -> None:
         lines_to_scroll = math.floor(self.lines_shown()) -1
@@ -118,10 +116,18 @@ class InnerBigText(QWidget):
             self.update()
             # print("-> %s,%s" %(self._selection_start_byte, self._selection_end_byte))
         line_number = self.y_pos_to_line(e.pos().y())
+        column_in_line = self.x_pos_to_column(e.pos().x())
         if line_number == 0:
             self.scroll_by_lines(-1)
         if line_number+1 >= int(self.lines_shown()):
             self.scroll_by_lines(1)
+        if column_in_line <= 1:
+            self._left_offset = max(0, self._left_offset-2)
+            self.update()
+        if column_in_line+1 >= self.columns_shown():
+            self._left_offset = self._left_offset+2
+            self.update()
+
 
     def h_scroll_event(self, left_offset: int):
         self._left_offset = left_offset
@@ -140,16 +146,26 @@ class InnerBigText(QWidget):
             maximum = max(0, length - width_in_chars+1)
             self.parent.h_scroll_bar.setMaximum(maximum)
 
-    def y_pos_to_line(self, y: int):
+    def y_pos_to_line(self, y: int) -> int:
         return int(y / self.char_height)
 
+    def x_pos_to_column(self, x: int) -> int:
+        return round(x / self.char_width)
+
+    def lines_shown(self) -> float:
+        return self.height() / float(self.char_height)
+
+    def columns_shown(self) -> float:
+        return self.width() / float(self.char_width)
+
+
     def to_byte_offset(self, e: QMouseEvent) -> int:
         line_number = self.y_pos_to_line(e.pos().y())
 
         if line_number < len(self.lines):
             line = self.lines[line_number]
-            char_in_line = round(e.pos().x() / self.char_width) + self._left_offset
-            char_in_line = min(char_in_line, line.length())
+            column_in_line = self.x_pos_to_column(e.pos().x()) + self._left_offset
+            char_in_line = min(column_in_line, line.length())
             # print("%s in line %s" % (char_in_line, line_number))
 
             current_byte = line.byte_offset() + char_in_line
@@ -158,10 +174,8 @@ class InnerBigText(QWidget):
             current_byte = self.model.byte_count()
         return current_byte
 
-    def lines_shown(self):
-        return self.height() / float(self.char_height)
 
-    def draw(self):
+    def paintEvent(self, event: QPaintEvent) -> None:
         painter = QPainter(self)
         painter.setFont(self.font)
         painter.setPen(QColor(0, 0, 0))