误打误撞

本来想画方格图，结果成这样

代码如下：

private void PaintMe()
       {
           int tWidth = this.Width;
           int tHeight = this.Height;
           Graphics g = this.CreateGraphics();
           g.FillRectangle(new SolidBrush(this.BackColor), 0, 0, tWidth, tHeight);

           int x = tWidth / m_GridSize.Width;
           int y = tHeight / m_GridSize.Height;
           Pen pGrid = new Pen(m_GridColor);
           int pos;      
           for (int i = 0 ; i <= x ; i++ )
           {
               pos = tWidth - (i * m_GridSize.Width + m_GridStartPos - 1);
               g.DrawLine(pGrid, 0, pos, pos, tHeight);
           }
           for (int i=0; i <= y; i++ )
           {
               pos = i * m_GridSize.Height - 1;
               g.DrawLine(pGrid, 0, pos, tWidth, pos);
           }
           int px = tWidth - m_GridMoveStep;
           int start = aList.Count - 2;
           Pen lGrid = new Pen(m_LineColor);
           while (start >= 0)
           {
               float f = (float)aList[start];
               float fPre = (float)aList[start+1];
               int h = (int)(tHeight - (tHeight * f));
               int hPre = (int)(tHeight - tHeight * fPre);
               g.DrawLine(lGrid, px, h, px + m_GridMoveStep, hPre);
               if (px < 0)
               {
                   break;
               }
               px -= m_GridMoveStep;
               start--;
           }

           g.Dispose();
       }