BitBlt - not for the faint-hearted...

Hi all, I am making a drawing prog which will place tiles in a square in a nxn grid of 32x32 squares.

The user simply drags a tile to where they want it and Voila!

However, so the user can see where their tile is gonna go (without drawing gridlines on the picture), I want an outline box to position itself where a tile would go as the user drags said tile around the picture.

I am using BitBlt to draw the tiles.

The following sub is called as the user drags a tile around the picture:

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Private Sub pictureFront_DragOver(Source As Control, X As Single, Y As Single, State As Integer)
X = (X - (X Mod 32))
Y = (Y - (Y Mod 32))

If ((X = lastX) And (Y = lastY)) Then Exit Sub

lastX = X
lastY = Y


'Draw the outline
BitBlt pictureDragOutlineBuffer.hDC, X, Y, dragOutlineBox.Width / 2, dragOutlineBox.Height, dragOutlineBox.hDC, dragOutlineBox.Width / 2, 0, vbSrcPaint 'The mask, important for transparency
BitBlt pictureDragOutlineBuffer.hDC, X, Y, dragOutlineBox.Width / 2, dragOutlineBox.Height, dragOutlineBox.hDC, 0, 0, vbSrcAnd 'The player himself

'Flip (Copy the buffer to the screen)
#1: BitBlt FrontDC, 0, 0, pictureFront.Width, pictureFront.Height, pictureDragOutlineBuffer.hDC, 0, 0, vbSrcCopy
#2: BitBlt FrontDC, 0, 0, pictureFront.Width, pictureFront.Height, BackDC, 0, 0, vbSrcCopy

Dim A, B
'Draw the background tiles
For A = 0 To pictureFront.Width / Tile.Width
For B = 0 To pictureFront.Height / Tile.Height
BitBlt pictureDragOutlineBuffer.hDC, A * Tile.Width, B * Tile.Height, Tile.Width, Tile.Height, Tile.hDC, 0, 0, vbSrcCopy 'Just copy the memory so no mask
Next
Next
End Sub

********************
However, this doesn't work very well.The lines marked #1 & #2 have the following effect:
#1: draws the pictureBox which has the outline in it onto the canvas
#2: draws the pictureBox which has the actual picture onto the canvas.

If I remove #1, I get no outline when dragging...
If remove #2, the actual picture draws itself over the outline as I go...


As you may have noticed, the outline and the actual picture are 'stored' in two different 'buffer' picture boxes...


Any suggestions?

Quote:

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Originally posted by rjlohan
If remove #2, the actual picture draws itself over the outline as I go...

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Or rather, if I remove #2, i can see the outline, but the picture only draws when I let go the mouse button. so this is no good, 'cause you can't see what you've already drawn...

Well, I'd do it like this:

1) Have a function which redraws all the tiles
2) In the MouseMove sub, call that sub and then draw the rectangle.

That should do it (it's how I did my map maker) ;)