|Rapid-Q Documentation by William Yu (c)1999||Chapter 12|
DECLARE SUB CanvasPaint (Sender AS QCanvas) CREATE Form AS QForm CREATE Canvas AS QCanvas OnPaint = CanvasPaint END CREATE ShowModal END CREATE SUB CanvasPaint (Sender AS QCanvas) Sender.FillRect(10,10,100,100,&HFF0000) '-- Blue box END SUBIf you try hiding the form under another Window and then refocus the program, the blue box will still appear. Now try writing something that doesn't utilize the OnPaint procedure:
CREATE Form AS QForm CREATE Canvas AS QCanvas FillRect(10,10,100,100,&HFF0000) '-- Blue box END CREATE Form.ShowModal END CREATENotice anything? Exactly, there is no blue box. The paint message was sent when your form first appears on your desktop, and since you didn't write any OnPaint procedure, there's nothing to draw. So what really happens to that FillRect code? Nothing really, it's still executed, but the next paint message offset it. To understand this better, try this code which will display the blue box when your press the button, but try hiding the window again or minimizing it. Redisplay your window and see what happens:
DECLARE SUB ButtonClick CREATE Form AS QForm CREATE Button AS QButton OnClick = ButtonClick END CREATE CREATE Canvas AS QCanvas END CREATE ShowModal END CREATE SUB ButtonClick Canvas.FillRect(10,10,100,100,&HFF0000) END SUBWhen you click your button the blue box will be drawn, however, once you hide part of the window and redisplay your window, you'll probably notice that your blue box has dissappeared.
DECLARE SUB CanvasPaint (Sender AS QCanvas) DECLARE SUB ButtonClick (Sender AS QButton) ' Create bitmap for off-screen use DIM BitMap AS QBITMAP BitMap.Height = 100 BitMap.Width = 100 BitMap.Paint(0,0,0,0) CREATE Form AS QForm Center Caption = "Simple graphics demonstration" CREATE Canvas AS QCanvas OnPaint = CanvasPaint END CREATE CREATE SquareButton AS QButton Caption = "Draw Square" OnClick = ButtonClick Left = 150 END CREATE CREATE CircleButton AS QButton Caption = "Draw Circle" OnClick = ButtonClick Left = 150 Top = 50 END CREATE CREATE LineButton AS QButton Caption = "Draw Line" OnClick = ButtonClick Left = 150 Top = 100 END CREATE ShowModal END CREATE SUB CanvasPaint (Sender AS QCanvas) Sender.Draw(0,0,Bitmap.BMP) END SUB SUB ButtonClick (Sender AS QButton) SELECT CASE Sender.Caption CASE "Draw Square" Bitmap.FillRect(10,10,50,50,&HFF0000) CASE "Draw Circle" Bitmap.Circle(10,60,50,110,&H0000FF,&H0000FF) CASE "Draw Line" Bitmap.Line(50,50,90,90,&H00FF00) END SELECT Canvas.Repaint '-- Tell Canvas to repaint itself. END SUB
SUB ListBoxDrawItem(Index AS INTEGER, State AS BYTE, Rect AS QRECT) IF State = 0 THEN '-- Selected ListBox.FillRect(Rect.Left, Rect.Top, Rect.Right, Rect.Bottom, &H00FF00) ELSE ListBox.FillRect(Rect.Left, Rect.Top, Rect.Right, Rect.Bottom, &HFFFFFF) END IF ListBox.TextOut(100, Rect.Top+(Rect.Bottom-Rect.Top)/4, ListBox.Item(index), 0, -1) ListBox.Draw(Rect.Left, Rect.Top, Bitmap(Index).BMP) END SUBHopefully the code is self explanatory, but a few things you may notice is that you don't paint the entire listbox (ie. all items), but rather a paint message is sent everytime an item is changed. This item occupies a rectangular region in your listbox, so what the OnDrawItem sends to you is the region of this item (this is the Rect parameter). You should not overstep this bound that has been given to you (ie. don't try to draw outside this region, it's not yours to draw on!). I have not covered QStringGrid in this section, but the same idea persists. You'll have to implement the OnDrawCell event, which is similar to the way you handle OnDrawItem in list/combo boxes.
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